AI Trajectory


Trajectory: (Expand/Collapse All)
Seq Timestamp Type Name Duration
0/0 2026/10/22 02:14 flow patch-triage
3m Args: 
null

Results: 
{
  "EnableConfigs": [
    "INET",
    "IPV6",
    "SYN_COOKIES"
  ],
  "FocusSymbols": [
    "tcp_set_rcvbuf",
    "tcp_disconnect",
    "do_tcp_setsockopt",
    "tcp_openreq_init_rwin",
    "tcp_connect_init",
    "cookie_v4_check",
    "cookie_v6_check"
  ],
  "KMSANReasoning": "The patch series resolves an issue where setting SO_RCVBUF unintentionally overwrote `tp-\u003ewindow_clamp`, causing TCP window calculations on connect, listen, or SYN cookies to mistake receive buffer adjustments for user-configured window clamps. To fix this, it adds `tp-\u003ewindow_clamp_user` to `struct tcp_sock` to track whether `TCP_WINDOW_CLAMP` was explicitly set by the user.\n\nKMSAN applicability assessment:\n1. Memory initialization: Sockets (`struct tcp_sock`) are allocated with `__GFP_ZERO` via `sk_alloc()` and cloned via `sock_copy()` in `sk_clone()`. The new field `window_clamp_user` is initialized to zero upon allocation, cleared on `tcp_disconnect()`, and set explicitly in `do_tcp_setsockopt()`. It is never read uninitialized.\n2. Kernel-to-user info leaks: The patch does not expose any new fields or structures to user space; `window_clamp_user` is an internal TCP state variable not copied to user space.\n3. Buffer parsing and length handling: The change modifies TCP window clamp calculations and route metric lookups (`tcp_req_window_clamp()`). No packet buffer slicing, payload accesses, or memory copying operations are altered in ways that could expose uninitialized buffer memory.\n\nBecause no uninitialized memory reads or information leak risks are introduced or exposed, dedicated KMSAN fuzzing is not required. Any functional or concurrency issues are sufficiently covered by packetdrill tests, KASAN, and KCSAN.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies TCP window clamp handling across connection initialization, socket options (TCP_WINDOW_CLAMP, SO_RCVBUF), connection reset/disconnect, request sockets, and IPv4/IPv6 SYN cookies in core networking. This executable logic is directly reachable by userspace socket syscalls in standard virtualized environments.",
  "WorthFuzzing": true
}
1/1 2026/10/22 02:14 action read-patch-diff
0m Args: 
null

Results: 
{
  "PatchDiff": "commit 3ad7cca995e47c2dfe2edb33638b17fb297e71c3\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Oct 22 02:14:36 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/Documentation/networking/net_cachelines/tcp_sock.rst b/Documentation/networking/net_cachelines/tcp_sock.rst\nindex 103328dc409e4..f317c7154d26f 100644\n--- a/Documentation/networking/net_cachelines/tcp_sock.rst\n+++ b/Documentation/networking/net_cachelines/tcp_sock.rst\n@@ -152,6 +152,7 @@ u32                           urg_seq\n unsigned_int                  keepalive_time\n unsigned_int                  keepalive_intvl\n int                           linger2\n+u32                           window_clamp_user\n u8                            bpf_sock_ops_cb_flags\n u8:1                          bpf_chg_cc_inprogress\n u16                           timeout_rehash\ndiff --git a/include/linux/tcp.h b/include/linux/tcp.h\nindex e4d1720f49f08..4f28fa6c4f4ea 100644\n--- a/include/linux/tcp.h\n+++ b/include/linux/tcp.h\n@@ -474,6 +474,7 @@ struct tcp_sock {\n \tunsigned int\t\tkeepalive_intvl;  /* time interval between keep alive probes */\n \n \tint\t\t\tlinger2;\n+\tu32\twindow_clamp_user; /* TCP_WINDOW_CLAMP set by the user, 0 if none */\n \n \n /* Sock_ops bpf program related variables */\ndiff --git a/include/net/tcp.h b/include/net/tcp.h\nindex 0265c27a5fd77..35b64fffd74bc 100644\n--- a/include/net/tcp.h\n+++ b/include/net/tcp.h\n@@ -1879,6 +1879,20 @@ extern void tcp_openreq_init_rwin(struct request_sock *req,\n \t\t\t\t  const struct sock *sk_listener,\n \t\t\t\t  const struct dst_entry *dst);\n \n+/* Window clamp for a request socket of listener @tp: the listener's clamp\n+ * if the user set one with TCP_WINDOW_CLAMP, else the route window metric.\n+ * The SYN-ACK and the SYN cookie paths must make the same choice, or the\n+ * child's window scale would not match the one sent in the SYN-ACK.\n+ * The listener is not locked here.\n+ */\n+static inline u32 tcp_req_window_clamp(const struct tcp_sock *tp,\n+\t\t\t\t       const struct dst_entry *dst)\n+{\n+\tif (READ_ONCE(tp-\u003ewindow_clamp_user))\n+\t\treturn READ_ONCE(tp-\u003ewindow_clamp);\n+\treturn dst_metric(dst, RTAX_WINDOW);\n+}\n+\n void tcp_enter_memory_pressure(struct sock *sk);\n void tcp_leave_memory_pressure(struct sock *sk);\n \ndiff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c\nindex 73e1297681847..6e78efbdc315f 100644\n--- a/net/ipv4/syncookies.c\n+++ b/net/ipv4/syncookies.c\n@@ -472,8 +472,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)\n \t}\n \n \t/* Try to redo what tcp_v4_send_synack did. */\n-\treq-\u003ersk_window_clamp = READ_ONCE(tp-\u003ewindow_clamp) ? :\n-\t\t\t\tdst_metric(\u0026rt-\u003edst, RTAX_WINDOW);\n+\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, \u0026rt-\u003edst);\n \t/* limit the window selection if the user enforce a smaller rx buffer */\n \tfull_space = tcp_full_space(sk);\n \tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\ndiff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c\nindex 99d7237a623d8..64465bc257d18 100644\n--- a/net/ipv4/tcp.c\n+++ b/net/ipv4/tcp.c\n@@ -1859,7 +1859,15 @@ int tcp_set_rcvlowat(struct sock *sk, int val)\n \n void tcp_set_rcvbuf(struct sock *sk, int val)\n {\n-\ttcp_set_window_clamp(sk, tcp_win_from_space(sk, val));\n+\tu32 user_clamp = tcp_sk(sk)-\u003ewindow_clamp_user;\n+\tint win = tcp_win_from_space(sk, val);\n+\n+\t/* window_clamp follows the receive buffer, but never goes above a\n+\t * clamp the user set with TCP_WINDOW_CLAMP.\n+\t */\n+\tif (user_clamp)\n+\t\twin = min_t(u32, win, user_clamp);\n+\ttcp_set_window_clamp(sk, win);\n }\n \n #ifdef CONFIG_MMU\n@@ -3429,6 +3437,7 @@ int tcp_disconnect(struct sock *sk, int flags)\n \ttp-\u003eis_cwnd_limited = 0;\n \ttp-\u003emax_packets_out = 0;\n \ttp-\u003ewindow_clamp = 0;\n+\tWRITE_ONCE(tp-\u003ewindow_clamp_user, 0);\n \ttp-\u003edelivered = 0;\n \ttp-\u003edelivered_ce = 0;\n \ttp-\u003eaccecn_fail_mode = 0;\n@@ -4058,6 +4067,9 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,\n \n \tcase TCP_WINDOW_CLAMP:\n \t\terr = tcp_set_window_clamp(sk, val);\n+\t\tif (!err)\n+\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp_user,\n+\t\t\t\t   val ? tp-\u003ewindow_clamp : 0);\n \t\tbreak;\n \n \tcase TCP_QUICKACK:\ndiff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c\nindex 0ddfd5af6e58f..c17dc5c464802 100644\n--- a/net/ipv4/tcp_minisocks.c\n+++ b/net/ipv4/tcp_minisocks.c\n@@ -435,15 +435,13 @@ void tcp_openreq_init_rwin(struct request_sock *req,\n \tstruct inet_request_sock *ireq = inet_rsk(req);\n \tconst struct tcp_sock *tp = tcp_sk(sk_listener);\n \tint full_space = tcp_full_space(sk_listener);\n-\tu32 window_clamp;\n \t__u8 rcv_wscale;\n \tu32 rcv_wnd;\n \tint mss;\n \n \tmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));\n-\twindow_clamp = READ_ONCE(tp-\u003ewindow_clamp);\n \t/* Set this up on the first call only */\n-\treq-\u003ersk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);\n+\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, dst);\n \n \t/* limit the window selection if the user enforce a smaller rx buffer */\n \tif (sk_listener-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\ndiff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c\nindex c8865205cdc8b..21b4ae303dd63 100644\n--- a/net/ipv4/tcp_output.c\n+++ b/net/ipv4/tcp_output.c\n@@ -4137,7 +4137,7 @@ static void tcp_connect_init(struct sock *sk)\n \n \ttcp_ca_dst_init(sk, dst);\n \n-\tif (!tp-\u003ewindow_clamp)\n+\tif (!tp-\u003ewindow_clamp_user)\n \t\tWRITE_ONCE(tp-\u003ewindow_clamp, dst_metric(dst, RTAX_WINDOW));\n \ttp-\u003eadvmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));\n \ndiff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c\nindex b581cb1ee2e8a..d7d61f8d25e55 100644\n--- a/net/ipv6/syncookies.c\n+++ b/net/ipv6/syncookies.c\n@@ -254,7 +254,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)\n \t\t}\n \t}\n \n-\treq-\u003ersk_window_clamp = READ_ONCE(tp-\u003ewindow_clamp) ? :dst_metric(dst, RTAX_WINDOW);\n+\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, dst);\n \t/* limit the window selection if the user enforce a smaller rx buffer */\n \tfull_space = tcp_full_space(sk);\n \tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt\nnew file mode 100644\nindex 0000000000000..b297294ed1659\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt\n@@ -0,0 +1,21 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// TCP_FASTOPEN_CONNECT defers the SYN until the first write(); between\n+// connect() and that write the socket is in TCP_SYN_SENT. SO_RCVBUF applied\n+// in that gap must not defeat the route \"window\" metric on the deferred SYN.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+sysctl -q net.ipv4.tcp_fastopen=5\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0\n+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_NO_COOKIE, [1], 4) = 0\n+   +0 connect(3, ..., ...) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0\n+   +0 write(3, ..., 1) = 1\n+\n+// The deferred SYN (carrying 1 byte of data) must advertise the route\n+// clamped window and window scale 0 (not win 65535, wscale 5).\n+   +0 \u003e S 0:1(1) win 2920 \u003cmss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0\u003e\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt\nnew file mode 100644\nindex 0000000000000..7ec7f14d8e896\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt\n@@ -0,0 +1,27 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// Setting SO_RCVBUF before connect() must not defeat the route \"window\"\n+// metric on the SYN.\n+//\n+// The route to the peer carries \"window 4096\" (RTAX_WINDOW). With SO_RCVBUF\n+// also set before connect(), the SYN the kernel sends must still advertise\n+// the small, route-clamped receive window and a window scale of 0 (the\n+// window scale option is sent, with a shift of 0).\n+//\n+// Since commit b025461303d8 (\"tcp: update window_clamp when SO_RCVBUF is\n+// set\"), setsockopt(SO_RCVBUF) wrote tp-\u003ewindow_clamp while the socket was\n+// still in TCP_CLOSE. tcp_connect_init() then treated that as a user clamp\n+// and skipped RTAX_WINDOW, so the SYN carried win 65535, wscale 5 instead.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0\n+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)\n+\n+// The SYN must advertise the route-clamped window and window scale 0.\n+   +0 \u003e S 0:0(0) win 2920 \u003cmss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0\u003e\n+  +.1 \u003c S. 0:0(0) ack 1 win 65535 \u003cmss 1460,nop,wscale 7\u003e\n+   +0 \u003e . 1:1(0) ack 1\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt\nnew file mode 100644\nindex 0000000000000..ed20a75fa9aab\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt\n@@ -0,0 +1,20 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// Passive side: SO_RCVBUF set on a listener must not defeat the route\n+// \"window\" metric on the SYN-ACK, and the child must use the window scale\n+// that the SYN-ACK advertised.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 bind(3, ..., ...) = 0\n+   +0 listen(3, 1) = 0\n+\n+   +0 \u003c S 0:0(0) win 65535 \u003cmss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7\u003e\n+   +0 \u003e S. 0:0(0) ack 1 win 2896 \u003cmss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0\u003e\n+ +.01 \u003c . 1:1(0) ack 1 win 514 \u003cnop,nop,TS val 110 ecr 100\u003e\n+   +0 accept(3, ..., ...) = 4\n+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt\nnew file mode 100644\nindex 0000000000000..e26f78704abcd\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt\n@@ -0,0 +1,22 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// SYN cookies: the child built by cookie_v4_check() must use the same\n+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and\n+// a route \"window\" metric, the SYN-ACK advertises window scale 0, so the\n+// child must use a receive window scale of 0 too.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+sysctl -q net.ipv4.tcp_syncookies=2\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 bind(3, ..., ...) = 0\n+   +0 listen(3, 10) = 0\n+\n+   +0 \u003c S 0:0(0) win 65535 \u003cmss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7\u003e\n+   +0 \u003e S. 0:0(0) ack 1 win 2896 \u003cmss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0\u003e\n+ +.01 \u003c . 1:1(0) ack 1 win 514 \u003cnop,nop,TS val 110 ecr 4000\u003e\n+   +0 accept(3, ..., ...) = 4\n+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt\nnew file mode 100644\nindex 0000000000000..8b5dd71d765fe\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt\n@@ -0,0 +1,22 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// SYN cookies: the child built by cookie_v6_check() must use the same\n+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and\n+// a route \"window\" metric, the SYN-ACK advertises window scale 0, so the\n+// child must use a receive window scale of 0 too.\n+--ip_version=ipv6\n+\n+`./defaults.sh\n+sysctl -q net.ipv4.tcp_syncookies=2\n+ip -6 route replace fd3d:fa7b:d17d::1 via fd3d:0a0b:17d6:8888::1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 bind(3, ..., ...) = 0\n+   +0 listen(3, 10) = 0\n+\n+   +0 \u003c S 0:0(0) win 65535 \u003cmss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7\u003e\n+   +0 \u003e S. 0:0(0) ack 1 win 2896 \u003cmss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0\u003e\n+ +.01 \u003c . 1:1(0) ack 1 win 514 \u003cnop,nop,TS val 110 ecr 4000\u003e\n+   +0 accept(3, ..., ...) = 4\n+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt\nnew file mode 100644\nindex 0000000000000..08ef005bf99a1\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt\n@@ -0,0 +1,27 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// After the handshake, tcp_init_buffer_space() lowers window_clamp to the\n+// receive space. A later, larger SO_RCVBUF must raise window_clamp again,\n+// but only up to the clamp the user set with TCP_WINDOW_CLAMP.\n+//\n+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.\n+--ip_version=ipv4\n+\n+`./defaults.sh`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_TCP, 10, [40000], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0\n+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0\n+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)\n+   +0 \u003e S 0:0(0) \u003c...\u003e\n+  +.1 \u003c S. 0:0(0) ack 1 win 65535 \u003cmss 1460,nop,wscale 7\u003e\n+   +0 \u003e . 1:1(0) ack 1\n+\n+// The small receive buffer keeps window_clamp below the user's clamp:\n+// 8192 (tcp_full_space()) minus the one segment (advmss 1460) that\n+// tcp_init_buffer_space() reserves.\n+   +0 getsockopt(3, SOL_TCP, 10, [6732], [4]) = 0\n+\n+// A larger SO_RCVBUF raises it again, up to the user's clamp.\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [212992], 4) = 0\n+   +0 getsockopt(3, SOL_TCP, 10, [40000], [4]) = 0\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt\nnew file mode 100644\nindex 0000000000000..458f2f313c7dd\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt\n@@ -0,0 +1,22 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// TCP_WINDOW_CLAMP set back to 0 on an unconnected socket removes the\n+// user's clamp: a later SO_RCVBUF must then not stop the route \"window\"\n+// metric from being applied on the SYN.\n+//\n+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0\n+   +0 setsockopt(3, SOL_TCP, 10, [0], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0\n+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)\n+\n+// No user clamp is left, so the SYN advertises the route window.\n+   +0 \u003e S 0:0(0) win 2920 \u003cmss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0\u003e\n+  +.1 \u003c S. 0:0(0) ack 1 win 65535 \u003cmss 1460,nop,wscale 7\u003e\n+   +0 \u003e . 1:1(0) ack 1\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt\nnew file mode 100644\nindex 0000000000000..69a05959e42eb\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt\n@@ -0,0 +1,23 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// A window clamp the user set with setsockopt(TCP_WINDOW_CLAMP) must be\n+// honoured on the SYN even when SO_RCVBUF is set afterwards on the still\n+// unconnected socket: SO_RCVBUF must not raise window_clamp above the\n+// user's clamp, and the route \"window\" metric must not replace it either.\n+//\n+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0\n+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)\n+\n+// The SYN advertises the user's clamp (win 16060), not the route window\n+// (2920) and not the SO_RCVBUF-derived full window.\n+   +0 \u003e S 0:0(0) win 16060 \u003cmss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0\u003e\n+  +.1 \u003c S. 0:0(0) ack 1 win 65535 \u003cmss 1460,nop,wscale 7\u003e\n+   +0 \u003e . 1:1(0) ack 1\ndiff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt\nnew file mode 100644\nindex 0000000000000..f7e7ddb5000d3\n--- /dev/null\n+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt\n@@ -0,0 +1,25 @@\n+// SPDX-License-Identifier: GPL-2.0\n+// Passive side: a TCP_WINDOW_CLAMP set on a listener must be honoured on\n+// the SYN-ACK even when SO_RCVBUF is set afterwards on the listener, and\n+// the route \"window\" metric must not replace it.\n+//\n+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.\n+--ip_version=ipv4\n+\n+`./defaults.sh\n+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`\n+\n+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3\n+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0\n+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0\n+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0\n+   +0 bind(3, ..., ...) = 0\n+   +0 listen(3, 1) = 0\n+\n+// The SYN-ACK advertises the user's clamp, not the route window and not\n+// the SO_RCVBUF-derived full window.\n+   +0 \u003c S 0:0(0) win 65535 \u003cmss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7\u003e\n+   +0 \u003e S. 0:0(0) ack 1 win 15928 \u003cmss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0\u003e\n+ +.01 \u003c . 1:1(0) ack 1 win 514 \u003cnop,nop,TS val 110 ecr 100\u003e\n+   +0 accept(3, ..., ...) = 4\n+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%\n"
}
2/1 2026/10/22 02:14 agent patch-evaluator
1m Model: 
core

Args: 
null

Results: 
{
  "EnableConfigs": [
    "INET",
    "IPV6",
    "SYN_COOKIES"
  ],
  "FocusSymbols": [
    "tcp_set_rcvbuf",
    "tcp_disconnect",
    "do_tcp_setsockopt",
    "tcp_openreq_init_rwin",
    "tcp_connect_init",
    "cookie_v4_check",
    "cookie_v6_check"
  ],
  "Reasoning": "The patch modifies TCP window clamp handling across connection initialization, socket options (TCP_WINDOW_CLAMP, SO_RCVBUF), connection reset/disconnect, request sockets, and IPv4/IPv6 SYN cookies in core networking. This executable logic is directly reachable by userspace socket syscalls in standard virtualized environments.",
  "WorthFuzzing": true
}

Instruction: 
You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.

================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.

- REACHABILITY IS THE PRIMARY GATE:
  Fuzzing can only discover bugs in code that can actually execute in standard virtualized
  environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
  If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
  regardless of whether it adds assertions or complex logic.

- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
  Patch authors routinely label changes as "cleanups", "refactorings", or state
  "No functional change intended". Do NOT take these claims at face value.
  Code refactorings that rearrange logic, introduce helper functions, or alter state management
  in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
  If reachable executable code is modified or refactored, it MUST be fuzzed.

- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
  When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
  BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
  Even if the author believes the invariant always holds, fuzzing is essential to verify whether
  an unusual sequence of operations can violate it.

================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:

- Non-kernel and non-executable changes:
  * Modifications to Documentation/, comments, or spelling fixes.
  * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
    that do not affect the compiled kernel image (vmlinux) or kernel modules.
  * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
    that do not alter control flow or data structures.
  * Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
  * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
    ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
  * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
    physical PCI hot-unplug or manual sysfs driver unbinding.
  * Code paths exclusive to architectures other than the target architecture.

================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
  * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
    BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
  * Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
  * Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
  * Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).

================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:

- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
  Do NOT list generic, ubiquitous functions called by almost every program in the corpus
  (including, but not limited to: general memory allocators and deallocators, page fault
  and trap handlers, or core synchronization primitives; this is not an exhaustive list).
  Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
  which severely dilutes fuzzing effort away from the actual changes.

- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
  List functions that specifically implement the logic being added or altered, or direct API entrypoints
  for the subsystem feature under review.

- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
  Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
  distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
  If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
  functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).

================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Prompt: 
Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 3ad7cca995e47c2dfe2edb33638b17fb297e71c3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Oct 22 02:14:36 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/networking/net_cachelines/tcp_sock.rst b/Documentation/networking/net_cachelines/tcp_sock.rst
index 103328dc409e4..f317c7154d26f 100644
--- a/Documentation/networking/net_cachelines/tcp_sock.rst
+++ b/Documentation/networking/net_cachelines/tcp_sock.rst
@@ -152,6 +152,7 @@ u32                           urg_seq
 unsigned_int                  keepalive_time
 unsigned_int                  keepalive_intvl
 int                           linger2
+u32                           window_clamp_user
 u8                            bpf_sock_ops_cb_flags
 u8:1                          bpf_chg_cc_inprogress
 u16                           timeout_rehash
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index e4d1720f49f08..4f28fa6c4f4ea 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -474,6 +474,7 @@ struct tcp_sock {
 	unsigned int		keepalive_intvl;  /* time interval between keep alive probes */
 
 	int			linger2;
+	u32	window_clamp_user; /* TCP_WINDOW_CLAMP set by the user, 0 if none */
 
 
 /* Sock_ops bpf program related variables */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0265c27a5fd77..35b64fffd74bc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1879,6 +1879,20 @@ extern void tcp_openreq_init_rwin(struct request_sock *req,
 				  const struct sock *sk_listener,
 				  const struct dst_entry *dst);
 
+/* Window clamp for a request socket of listener @tp: the listener's clamp
+ * if the user set one with TCP_WINDOW_CLAMP, else the route window metric.
+ * The SYN-ACK and the SYN cookie paths must make the same choice, or the
+ * child's window scale would not match the one sent in the SYN-ACK.
+ * The listener is not locked here.
+ */
+static inline u32 tcp_req_window_clamp(const struct tcp_sock *tp,
+				       const struct dst_entry *dst)
+{
+	if (READ_ONCE(tp->window_clamp_user))
+		return READ_ONCE(tp->window_clamp);
+	return dst_metric(dst, RTAX_WINDOW);
+}
+
 void tcp_enter_memory_pressure(struct sock *sk);
 void tcp_leave_memory_pressure(struct sock *sk);
 
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 73e1297681847..6e78efbdc315f 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -472,8 +472,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	}
 
 	/* Try to redo what tcp_v4_send_synack did. */
-	req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :
-				dst_metric(&rt->dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, &rt->dst);
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	full_space = tcp_full_space(sk);
 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 99d7237a623d8..64465bc257d18 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1859,7 +1859,15 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
 
 void tcp_set_rcvbuf(struct sock *sk, int val)
 {
-	tcp_set_window_clamp(sk, tcp_win_from_space(sk, val));
+	u32 user_clamp = tcp_sk(sk)->window_clamp_user;
+	int win = tcp_win_from_space(sk, val);
+
+	/* window_clamp follows the receive buffer, but never goes above a
+	 * clamp the user set with TCP_WINDOW_CLAMP.
+	 */
+	if (user_clamp)
+		win = min_t(u32, win, user_clamp);
+	tcp_set_window_clamp(sk, win);
 }
 
 #ifdef CONFIG_MMU
@@ -3429,6 +3437,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->is_cwnd_limited = 0;
 	tp->max_packets_out = 0;
 	tp->window_clamp = 0;
+	WRITE_ONCE(tp->window_clamp_user, 0);
 	tp->delivered = 0;
 	tp->delivered_ce = 0;
 	tp->accecn_fail_mode = 0;
@@ -4058,6 +4067,9 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 
 	case TCP_WINDOW_CLAMP:
 		err = tcp_set_window_clamp(sk, val);
+		if (!err)
+			WRITE_ONCE(tp->window_clamp_user,
+				   val ? tp->window_clamp : 0);
 		break;
 
 	case TCP_QUICKACK:
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 0ddfd5af6e58f..c17dc5c464802 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -435,15 +435,13 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 	struct inet_request_sock *ireq = inet_rsk(req);
 	const struct tcp_sock *tp = tcp_sk(sk_listener);
 	int full_space = tcp_full_space(sk_listener);
-	u32 window_clamp;
 	__u8 rcv_wscale;
 	u32 rcv_wnd;
 	int mss;
 
 	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
-	window_clamp = READ_ONCE(tp->window_clamp);
 	/* Set this up on the first call only */
-	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, dst);
 
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c8865205cdc8b..21b4ae303dd63 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -4137,7 +4137,7 @@ static void tcp_connect_init(struct sock *sk)
 
 	tcp_ca_dst_init(sk, dst);
 
-	if (!tp->window_clamp)
+	if (!tp->window_clamp_user)
 		WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
 	tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index b581cb1ee2e8a..d7d61f8d25e55 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -254,7 +254,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		}
 	}
 
-	req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, dst);
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	full_space = tcp_full_space(sk);
 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
new file mode 100644
index 0000000000000..b297294ed1659
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_FASTOPEN_CONNECT defers the SYN until the first write(); between
+// connect() and that write the socket is in TCP_SYN_SENT. SO_RCVBUF applied
+// in that gap must not defeat the route "window" metric on the deferred SYN.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_fastopen=5
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_NO_COOKIE, [1], 4) = 0
+   +0 connect(3, ..., ...) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 write(3, ..., 1) = 1
+
+// The deferred SYN (carrying 1 byte of data) must advertise the route
+// clamped window and window scale 0 (not win 65535, wscale 5).
+   +0 > S 0:1(1) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
new file mode 100644
index 0000000000000..7ec7f14d8e896
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// Setting SO_RCVBUF before connect() must not defeat the route "window"
+// metric on the SYN.
+//
+// The route to the peer carries "window 4096" (RTAX_WINDOW). With SO_RCVBUF
+// also set before connect(), the SYN the kernel sends must still advertise
+// the small, route-clamped receive window and a window scale of 0 (the
+// window scale option is sent, with a shift of 0).
+//
+// Since commit b025461303d8 ("tcp: update window_clamp when SO_RCVBUF is
+// set"), setsockopt(SO_RCVBUF) wrote tp->window_clamp while the socket was
+// still in TCP_CLOSE. tcp_connect_init() then treated that as a user clamp
+// and skipped RTAX_WINDOW, so the SYN carried win 65535, wscale 5 instead.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN must advertise the route-clamped window and window scale 0.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
new file mode 100644
index 0000000000000..ed20a75fa9aab
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: SO_RCVBUF set on a listener must not defeat the route
+// "window" metric on the SYN-ACK, and the child must use the window scale
+// that the SYN-ACK advertised.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
new file mode 100644
index 0000000000000..e26f78704abcd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v4_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
new file mode 100644
index 0000000000000..8b5dd71d765fe
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v6_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv6
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip -6 route replace fd3d:fa7b:d17d::1 via fd3d:0a0b:17d6:8888::1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
new file mode 100644
index 0000000000000..08ef005bf99a1
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// After the handshake, tcp_init_buffer_space() lowers window_clamp to the
+// receive space. A later, larger SO_RCVBUF must raise window_clamp again,
+// but only up to the clamp the user set with TCP_WINDOW_CLAMP.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [40000], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+   +0 > S 0:0(0) <...>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
+
+// The small receive buffer keeps window_clamp below the user's clamp:
+// 8192 (tcp_full_space()) minus the one segment (advmss 1460) that
+// tcp_init_buffer_space() reserves.
+   +0 getsockopt(3, SOL_TCP, 10, [6732], [4]) = 0
+
+// A larger SO_RCVBUF raises it again, up to the user's clamp.
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [212992], 4) = 0
+   +0 getsockopt(3, SOL_TCP, 10, [40000], [4]) = 0
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
new file mode 100644
index 0000000000000..458f2f313c7dd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_WINDOW_CLAMP set back to 0 on an unconnected socket removes the
+// user's clamp: a later SO_RCVBUF must then not stop the route "window"
+// metric from being applied on the SYN.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [0], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// No user clamp is left, so the SYN advertises the route window.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
new file mode 100644
index 0000000000000..69a05959e42eb
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+// A window clamp the user set with setsockopt(TCP_WINDOW_CLAMP) must be
+// honoured on the SYN even when SO_RCVBUF is set afterwards on the still
+// unconnected socket: SO_RCVBUF must not raise window_clamp above the
+// user's clamp, and the route "window" metric must not replace it either.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN advertises the user's clamp (win 16060), not the route window
+// (2920) and not the SO_RCVBUF-derived full window.
+   +0 > S 0:0(0) win 16060 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
new file mode 100644
index 0000000000000..f7e7ddb5000d3
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: a TCP_WINDOW_CLAMP set on a listener must be honoured on
+// the SYN-ACK even when SO_RCVBUF is set afterwards on the listener, and
+// the route "window" metric must not replace it.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+// The SYN-ACK advertises the user's clamp, not the route window and not
+// the SO_RCVBUF-derived full window.
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 15928 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%

3/2 2026/10/22 02:14 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 10775
							output: 36
							thoughts: 464

Thoughts: 
**Analyzing a Kernel Networking Patch for Fuzzing Potential**

Okay, so this patch dives right into the heart of the TCP stack, touching crucial files like `tcp.h`, `syncookies.c`, `tcp.c`, and `tcp_output.c`, both in the IPv4 and IPv6 domains.  That immediately flags it as interesting – any modification to core networking code is worth a closer look. I need to understand exactly what's changed and whether it introduces any new surface area for vulnerabilities.

Specifically, it looks like they've introduced a new field, `window_clamp_user`, within the `tcp_sock` structure.  There's also a new helper function, `tcp_req_window_clamp`.  I need to figure out the purpose of this clamp. The updates to `cookie_v4_check`, `tcp_set_rcvbuf`, `tcp_disconnect`, `do_tcp_setsockopt`, `tcp_openreq_init_rwin`, and `tcp_connect_init` are key; they likely represent the integration points for this new functionality.  I'll examine how this `window_clamp_user` affects things like SYN cookies, receive buffer management, and connection initialization.

Given that this is core TCP networking within the Linux kernel, specifically the `net/ipv4` and `net/ipv6` directories, and directly interacts with the standard sockets interface (`AF_INET`, `AF_INET6`, `SOCK_STREAM`), and system calls like `setsockopt`, `connect`, `listen`, and `accept`, it’s clear that it's user-accessible.  This means this code is executable and handles user-provided data.  The scope is definitely "Core Subsystems: core networking," meaning this is high-priority for fuzzing. *WorthFuzzing* is a resounding "yes".

Now, I need to dig into the details to understand what specific kernel configurations are required to trigger this code and what function names or symbols I should focus on when configuring a fuzzer. I'll probably use `grepper` or check the git logs and file revisions for that information.

4/2 2026/10/22 02:14 tool grepper
0m Args: 
{
  "Expression": "tcp_set_rcvbuf",
  "PathPrefixes": [
    "net/ipv4/tcp.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp.c=1832=int tcp_set_rcvlowat(struct sock *sk, int val)\n--\nnet/ipv4/tcp.c-1859-\nnet/ipv4/tcp.c:1860:void tcp_set_rcvbuf(struct sock *sk, int val)\nnet/ipv4/tcp.c-1861-{\n"
}
5/2 2026/10/22 02:14 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 11842
							output: 21
							thoughts: 16

Thoughts: 
Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the Code Change: Digging Deeper**

Alright, I'm taking a look at this patch. My initial instinct is to *really* understand the "why" and "how" behind this change before I even start reviewing the code itself. The commit message *should* provide some context, but we all know those can be... variable in quality. So, first things first, I'm going to leverage my Git chops. I need the full picture. Let's start with a quick glance at the commit message; often the title won't tell me enough, so I'll be looking for details in the description. If that's not enough – or if the commit message is just plain cryptic (which, let's be honest, happens) – I'm immediately moving on to `git show` to get the diff and more context, including metadata that might be buried in the commit. I'm after the bigger story. I'm not just looking for what was *changed*, but also the *reason* for the change, any related issues, potential side effects considered, and if there are any obvious implications for existing functionality or performance. This foundational information will guide my subsequent, in-depth code review.

6/2 2026/10/22 02:14 tool grepper
0m Args: 
{
  "Expression": "tcp_req_window_clamp"
}

Results: 
{
  "Output": "include/net/tcp.h=1878=extern void tcp_openreq_init_rwin(struct request_sock *req,\n--\ninclude/net/tcp.h-1887- */\ninclude/net/tcp.h:1888:static inline u32 tcp_req_window_clamp(const struct tcp_sock *tp,\ninclude/net/tcp.h-1889-\t\t\t\t       const struct dst_entry *dst)\n--\nnet/ipv4/syncookies.c=405=struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv4/syncookies.c-474-\t/* Try to redo what tcp_v4_send_synack did. */\nnet/ipv4/syncookies.c:475:\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, \u0026rt-\u003edst);\nnet/ipv4/syncookies.c-476-\t/* limit the window selection if the user enforce a smaller rx buffer */\n--\nnet/ipv4/tcp_minisocks.c=431=void tcp_openreq_init_rwin(struct request_sock *req,\n--\nnet/ipv4/tcp_minisocks.c-443-\t/* Set this up on the first call only */\nnet/ipv4/tcp_minisocks.c:444:\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, dst);\nnet/ipv4/tcp_minisocks.c-445-\n--\nnet/ipv6/syncookies.c=174=struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv6/syncookies.c-256-\nnet/ipv6/syncookies.c:257:\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, dst);\nnet/ipv6/syncookies.c-258-\t/* limit the window selection if the user enforce a smaller rx buffer */\n"
}
7/2 2026/10/22 02:14 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 12686
							output: 21
							thoughts: 28

Thoughts: 
Okay, here's my take on those thoughts, framed as an expert diving into the code:

**Investigating `tcp_set_rcvbuf` Usage**

Alright, time to get to the bottom of this. I need to understand the landscape surrounding `tcp_set_rcvbuf`. Specifically, I want to know, and fast, *who* is calling this function? What parts of the networking stack, or potentially even user-space code, are directly interacting with the receive buffer size configuration? Understanding the call sites is the crucial first step to grasping its behavior, identifying potential performance bottlenecks, or maybe even uncovering some unexpected interactions. Let's trace those callers and get a lay of the land.

8/2 2026/10/22 02:14 tool grepper
0m Args: 
{
  "Expression": "tcp_set_rcvbuf"
}

Results: 
{
  "Output": "include/net/tcp.h=515=int tcp_set_rcvlowat(struct sock *sk, int val);\ninclude/net/tcp.h:516:void tcp_set_rcvbuf(struct sock *sk, int val);\ninclude/net/tcp.h-517-int tcp_set_window_clamp(struct sock *sk, int val);\n--\nnet/ipv4/af_inet.c=1057=const struct proto_ops inet_stream_ops = {\n--\nnet/ipv4/af_inet.c-1088-\t.set_rcvlowat\t   = tcp_set_rcvlowat,\nnet/ipv4/af_inet.c:1089:\t.set_rcvbuf\t   = tcp_set_rcvbuf,\nnet/ipv4/af_inet.c-1090-};\n--\nnet/ipv4/tcp.c=1832=int tcp_set_rcvlowat(struct sock *sk, int val)\n--\nnet/ipv4/tcp.c-1859-\nnet/ipv4/tcp.c:1860:void tcp_set_rcvbuf(struct sock *sk, int val)\nnet/ipv4/tcp.c-1861-{\n--\nnet/ipv6/af_inet6.c=656=const struct proto_ops inet6_stream_ops = {\n--\nnet/ipv6/af_inet6.c-687-\t.set_rcvlowat\t   = tcp_set_rcvlowat,\nnet/ipv6/af_inet6.c:688:\t.set_rcvbuf\t   = tcp_set_rcvbuf,\nnet/ipv6/af_inet6.c-689-};\n--\nnet/mptcp/sockopt.c=70=static void __mptcp_subflow_set_rcvbuf(struct sock *ssk, int val)\n--\nnet/mptcp/sockopt.c-72-\tWRITE_ONCE(ssk-\u003esk_rcvbuf, val);\nnet/mptcp/sockopt.c:73:\ttcp_set_rcvbuf(ssk, val);\nnet/mptcp/sockopt.c-74-}\n"
}
9/2 2026/10/22 02:14 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 13449
							output: 34
							thoughts: 116

Thoughts: 
Okay, let's break this down.

**Investigating the `SO_RCVBUF` Setting in TCP**

Alright, so `tcp_set_rcvbuf` is clearly the target of the `SO_RCVBUF` option. I remember that the path to this function is something like, `setsockopt` which calls `sock->ops->set_rcvbuf`.  This seems to be the crucial link.  Now, the real question is, just *where* exactly is the `set_rcvbuf` function pointer within the `proto_ops` structure being used? It's time to trace the execution.

Okay, so I should start with where the socket options are handled in general, since this is a common approach. Let's look at `net/core/sock.c`.  I know it's probably one of these paths: either `sock_set_rcvbuf`,  or something involving `sk->sk_prot`, or the direct call I mentioned before, `sock->ops->set_rcvbuf`.  Got it. I'll check these potential calling locations.

10/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "-\u003eset_rcvbuf",
  "PathPrefixes": [
    "net/core/sock.c"
  ]
}

Results: 
{
  "Output": "net/core/sock.c=968=static void __sock_set_rcvbuf(struct sock *sk, int val)\n--\nnet/core/sock.c-992-\nnet/core/sock.c:993:\t\tif (ops-\u003eset_rcvbuf)\nnet/core/sock.c:994:\t\t\tops-\u003eset_rcvbuf(sk, sk-\u003esk_rcvbuf);\nnet/core/sock.c-995-\t}\n"
}
11/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 13969
							output: 33
							thoughts: 32

Thoughts: 
Here's my take on the thought process:

**Diving into TCP Configuration**

Okay, so we're dealing with `do_tcp_setsockopt` here, specifically focusing on its interaction with `TCP_WINDOW_CLAMP`. I know this is where we control the advertised receive window size, so I need to make sure this is handled correctly. Let's dig deeper into the implementation of `tcp_set_window_clamp`. I'll want to review how the clamp value is set and how it interacts with other TCP parameters. My initial thought is it's probably where the socket option is set or read, I need to make sure there are not any interactions with other features. I'm going to quickly refresh the relevant parts of the TCP RFCs to ensure I have all the context I need. It's time to thoroughly verify its behavior.

12/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "tcp_set_window_clamp",
  "PathPrefixes": [
    "net/ipv4/"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp.c=1860=void tcp_set_rcvbuf(struct sock *sk, int val)\n--\nnet/ipv4/tcp.c-1869-\t\twin = min_t(u32, win, user_clamp);\nnet/ipv4/tcp.c:1870:\ttcp_set_window_clamp(sk, win);\nnet/ipv4/tcp.c-1871-}\n--\nnet/ipv4/tcp.c=3800=EXPORT_SYMBOL(tcp_sock_set_keepcnt);\nnet/ipv4/tcp.c-3801-\nnet/ipv4/tcp.c:3802:int tcp_set_window_clamp(struct sock *sk, int val)\nnet/ipv4/tcp.c-3803-{\n--\nnet/ipv4/tcp.c=3850=int do_tcp_setsockopt(struct sock *sk, int level, int optname,\n--\nnet/ipv4/tcp.c-4068-\tcase TCP_WINDOW_CLAMP:\nnet/ipv4/tcp.c:4069:\t\terr = tcp_set_window_clamp(sk, val);\nnet/ipv4/tcp.c-4070-\t\tif (!err)\n"
}
13/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 14541
							output: 37
							thoughts: 24

Thoughts: 
Okay, here's my take on those thoughts, tailored for an expert audience:

**Diving into the TCP Window Clamp Function**

Alright, let's get down to brass tacks. I'm thinking I need to refresh my memory on how `tcp_set_window_clamp` is implemented within `net/ipv4/tcp.c`. It's a key function for managing congestion control and window sizing, so I want to ensure I've got a firm grasp on its mechanics, especially in relation to [mention a relevant specific concern, e.g., "how it interacts with the newer BBR congestion control algorithm," or "its impact on high-bandwidth, long-delay paths"]. The goal is to fully understand its impact in the current context. I need to refresh the details of its role in overall throughput and latency, and any interactions with modern algorithms or hardware considerations. Going to dive into the code.

14/2 2026/10/22 02:15 tool read-file
0m Args: 
{
  "File": "net/ipv4/tcp.c",
  "FirstLine": 3800,
  "LineCount": 40
}

Results: 
{
  "Contents": "3800:\tEXPORT_SYMBOL(tcp_sock_set_keepcnt);\n3801:\t\n3802:\tint tcp_set_window_clamp(struct sock *sk, int val)\n3803:\t{\n3804:\t\tu32 old_window_clamp, new_window_clamp, new_rcv_ssthresh;\n3805:\t\tstruct tcp_sock *tp = tcp_sk(sk);\n3806:\t\n3807:\t\tif (!val) {\n3808:\t\t\tif (sk-\u003esk_state != TCP_CLOSE)\n3809:\t\t\t\treturn -EINVAL;\n3810:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, 0);\n3811:\t\t\treturn 0;\n3812:\t\t}\n3813:\t\n3814:\t\told_window_clamp = tp-\u003ewindow_clamp;\n3815:\t\tnew_window_clamp = max_t(int, SOCK_MIN_RCVBUF / 2, val);\n3816:\t\n3817:\t\tif (new_window_clamp == old_window_clamp)\n3818:\t\t\treturn 0;\n3819:\t\n3820:\t\tWRITE_ONCE(tp-\u003ewindow_clamp, new_window_clamp);\n3821:\t\n3822:\t\t/* Need to apply the reserved mem provisioning only\n3823:\t\t * when shrinking the window clamp.\n3824:\t\t */\n3825:\t\tif (new_window_clamp \u003c old_window_clamp) {\n3826:\t\t\t__tcp_adjust_rcv_ssthresh(sk, new_window_clamp);\n3827:\t\t} else {\n3828:\t\t\tnew_rcv_ssthresh = min(tp-\u003ercv_wnd, new_window_clamp);\n3829:\t\t\ttp-\u003ercv_ssthresh = max(new_rcv_ssthresh, tp-\u003ercv_ssthresh);\n3830:\t\t}\n3831:\t\treturn 0;\n3832:\t}\n3833:\t\n3834:\tint tcp_sock_set_maxseg(struct sock *sk, int val)\n3835:\t{\n3836:\t\t/* Values greater than interface MTU won't take effect. However\n3837:\t\t * at the point when this call is done we typically don't yet\n3838:\t\t * know which interface is going to be used\n3839:\t\t */\n"
}
15/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 15442
							output: 39
							thoughts: 11

Thoughts: 
Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:

**Diving into `tcp_connect_init`**

Alright, time to get my hands dirty. Let's start with a thorough examination of `tcp_connect_init`. I know this function is crucial for setting up the initial connection process, and understanding its behavior is key to diagnosing any potential connection-related issues. I'm thinking about its role in the 3-way handshake sequence, specifically how it handles the SYN segment, and if it's responsible for things like setting the initial sequence number, and configuring TCP options. I need to refresh my memory on the internal data structures it manipulates, and the state transitions it triggers. I need to look at its interactions with the socket layer, and how it handles different error conditions like timeout or RST received. I anticipate looking at how it integrates with the more general connection establishment framework, especially regarding socket address binding and port selection. Let's see what we can find.

16/2 2026/10/22 02:15 tool read-file
0m Args: 
{
  "File": "net/ipv4/tcp_output.c",
  "FirstLine": 4130,
  "LineCount": 30
}

Results: 
{
  "Contents": "4130:\t\t/* If user gave his TCP_MAXSEG, record it to clamp */\n4131:\t\tuser_mss = READ_ONCE(tp-\u003erx_opt.user_mss);\n4132:\t\tif (user_mss)\n4133:\t\t\ttp-\u003erx_opt.mss_clamp = user_mss;\n4134:\t\ttp-\u003emax_window = 0;\n4135:\t\ttcp_mtup_init(sk);\n4136:\t\ttcp_sync_mss(sk, dst_mtu(dst));\n4137:\t\n4138:\t\ttcp_ca_dst_init(sk, dst);\n4139:\t\n4140:\t\tif (!tp-\u003ewindow_clamp_user)\n4141:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, dst_metric(dst, RTAX_WINDOW));\n4142:\t\ttp-\u003eadvmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));\n4143:\t\n4144:\t\ttcp_initialize_rcv_mss(sk);\n4145:\t\n4146:\t\t/* limit the window selection if the user enforce a smaller rx buffer */\n4147:\t\tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\n4148:\t\t    (tp-\u003ewindow_clamp \u003e tcp_full_space(sk) || tp-\u003ewindow_clamp == 0))\n4149:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, tcp_full_space(sk));\n4150:\t\n4151:\t\trcv_wnd = tcp_rwnd_init_bpf(sk);\n4152:\t\tfull_space = tcp_full_space(sk);\n4153:\t\tif (rcv_wnd == 0)\n4154:\t\t\trcv_wnd = dst_metric(dst, RTAX_INITRWND);\n4155:\t\telse if (full_space \u003c (u64)rcv_wnd * tp-\u003eadvmss)\n4156:\t\t\tfull_space = min_t(u64, (u64)rcv_wnd * tp-\u003eadvmss, INT_MAX);\n4157:\t\n4158:\t\ttcp_select_initial_window(sk, full_space,\n4159:\t\t\t\t\t  tp-\u003eadvmss - (tp-\u003erx_opt.ts_recent_stamp ? tp-\u003etcp_header_len - sizeof(struct tcphdr) : 0),\n"
}
17/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 16337
							output: 39
							thoughts: 564

Thoughts: 
**Analyzing TCP Window Clamp and Fuzzing Potential**

Okay, let's dive into this. My initial thought is to examine the `net/ipv4/syncookies.c` and `net/ipv6/syncookies.c` files. Specifically, I'm interested in how the window clamp is handled during SYN cookie verification. In `net/ipv4/syncookies.c`, `cookie_v4_check` uses `tcp_req_window_clamp`, and similarly, `cookie_v6_check` in `net/ipv6/syncookies.c` and `tcp_openreq_init_rwin` in `net/ipv4/tcp_minisocks.c` calls `tcp_req_window_clamp`. This is consistent.

Now, let's dissect `tcp_req_window_clamp`. It appears to be a static inline function defined in `include/net/tcp.h`. The critical part is that it checks `tp->window_clamp_user`. If that's set, it uses `tp->window_clamp`; otherwise, it defaults to `dst_metric(dst, RTAX_WINDOW)`.

Next, I need to evaluate the fuzzing potential. Is this a worthwhile target? Absolutely. This code is fundamental. It's used in `AF_INET`, `AF_INET6`, standard TCP sockets, standard TCP `setsockopt` with `SO_RCVBUF`, `TCP_WINDOW_CLAMP`, connection establishment, SYN cookies, and disconnection. It's incredibly reachable, even in a basic QEMU VM. So, `WorthFuzzing` is unequivocally `true`.

Now, for the configuration requirements. We need to ensure the necessary modules are built. We know:

*   `INET` (CONFIG\_INET) is essential, providing IPv4 and TCP.
*   `IPV6` (CONFIG\_IPV6) is required for `net/ipv6/syncookies.c` to be compiled.
*   And, finally, `SYN_COOKIES` (CONFIG\_SYN\_COOKIES) controls the inclusion of the SYN cookie code in both IPv4 and IPv6.

I'll double-check `net/ipv4/Makefile` and `net/ipv6/Makefile` to confirm the dependencies, but it looks straightforward. This seems like a promising area for focused fuzzing.

18/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "syncookies",
  "PathPrefixes": [
    "net/ipv4/Makefile",
    "net/ipv6/Makefile"
  ]
}

Results: 
{
  "Output": "net/ipv4/Makefile=33=obj-$(CONFIG_NET_IPVTI) += ip_vti.o\nnet/ipv4/Makefile:34:obj-$(CONFIG_SYN_COOKIES) += syncookies.o\nnet/ipv4/Makefile-35-obj-$(CONFIG_INET_AH) += ah4.o\n--\nnet/ipv6/Makefile=22=ipv6-$(CONFIG_PROC_FS) += proc.o\nnet/ipv6/Makefile:23:ipv6-$(CONFIG_SYN_COOKIES) += syncookies.o\nnet/ipv6/Makefile-24-ipv6-$(CONFIG_NETLABEL) += calipso.o\n"
}
19/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 17625
							output: 33
							thoughts: 25

Thoughts: 
Okay, here's my take on those thoughts, tailored for an expert audience:

**Kernel Configuration Context: SYN Cookies**

Ah, `CONFIG_SYN_COOKIES`! That's a key setting, immediately flags the need for deeper context and implications. My mind jumps straight to Kconfig. I want to quickly verify the current state of that particular configuration option. I need to refresh my understanding of how this setting is currently enabled or disabled. This will give me all the information I need, if the kernel is currently configured for it, and what else might affect it.

20/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "config SYN_COOKIES",
  "PathPrefixes": [
    "net/ipv4/Kconfig"
  ]
}

Results: 
{
  "Output": "net/ipv4/Kconfig=259=config IP_PIMSM_V2\n--\nnet/ipv4/Kconfig-267-\nnet/ipv4/Kconfig:268:config SYN_COOKIES\nnet/ipv4/Kconfig-269-\tbool \"IP: TCP syncookie support\"\n"
}
21/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 17894
							output: 35
							thoughts: 20

Thoughts: 
Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Examining IPv4 Configuration Options**

Okay, let's dive in. I need to refresh my memory on some of the IPv4 configuration options, specifically the ones related to a recent discussion. I'm going to jump into the `net/ipv4/Kconfig` file, specifically around line 268. I'm expecting to find the relevant configurations there. I'm hoping this will jog my memory on the interactions of those options. I know where to find the source. Let me get right to it.

22/2 2026/10/22 02:15 tool read-file
0m Args: 
{
  "File": "net/ipv4/Kconfig",
  "FirstLine": 265,
  "LineCount": 20
}

Results: 
{
  "Contents": " 265:\t\t  gated-5). This routing protocol is not used widely, so say N unless\n 266:\t\t  you want to play with it.\n 267:\t\n 268:\tconfig SYN_COOKIES\n 269:\t\tbool \"IP: TCP syncookie support\"\n 270:\t\thelp\n 271:\t\t  Normal TCP/IP networking is open to an attack known as \"SYN\n 272:\t\t  flooding\". This denial-of-service attack prevents legitimate remote\n 273:\t\t  users from being able to connect to your computer during an ongoing\n 274:\t\t  attack and requires very little work from the attacker, who can\n 275:\t\t  operate from anywhere on the Internet.\n 276:\t\n 277:\t\t  SYN cookies provide protection against this type of attack. If you\n 278:\t\t  say Y here, the TCP/IP stack will use a cryptographic challenge\n 279:\t\t  protocol known as \"SYN cookies\" to enable legitimate users to\n 280:\t\t  continue to connect, even when your machine is under attack. There\n 281:\t\t  is no need for the legitimate users to change their TCP/IP software;\n 282:\t\t  SYN cookies work transparently to them. For technical information\n 283:\t\t  about SYN cookies, check out \u003chttps://cr.yp.to/syncookies.html\u003e.\n 284:\t\n"
}
23/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 18440
							output: 39
							thoughts: 438

Thoughts: 
**Analyzing TCP Window Clamping and SYN Cookies**

Okay, so I'm looking at these configurations: `INET`, `IPV6`, and `SYN_COOKIES`. It seems pretty clear that `SYN_COOKIES` is conditionally compiled under `if INET` within `net/ipv4/Kconfig`. And, interestingly, enabling `IPV6` allows for `net/ipv6/syncookies.c` to be used, but only if `SYN_COOKIES` is also enabled. So those three configs are definitely the key players here.

Now, let's dive into these "FocusSymbols". The goal here is to understand the implications of the changes. Specifically, I need to know what symbols were directly modified, or that call the modified static inlines. Time for a careful review of the diff.

Alright, starting with `net/ipv4/tcp.c`:

1.  We have `tcp_set_rcvbuf`. Okay, the modification here appears to involve checking `window_clamp_user` and clamping the `win` value.
2.  Next, `tcp_disconnect` has been altered. This one is resetting `window_clamp_user` to 0.
3.  Finally, `do_tcp_setsockopt` which is setting `window_clamp_user` when `TCP_WINDOW_CLAMP` is used.

Hang on a second. Now that I have this list, what's calling these functions? `tcp_set_rcvbuf` seems relatively isolated, that's good to know. `tcp_disconnect` occurs during disconnects, like a `connect(AF_UNSPEC)` call. And, wait, `tcp_setsockopt` calls `do_tcp_setsockopt`... I need to correct my notes here. It's actually `do_tcp_setsockopt` that's the function that has been directly modified.

Okay, let's keep going. `net/ipv4/tcp_output.c`:

1.  `tcp_connect_init` has a change: `if (!tp->window_clamp_user) WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));`. Okay, so it seems to be setting the window clamp. Now, a key question: Is `tcp_connect_init` static, or is it exposed somehow? I need to check if it's static, exported, or inlined – that has major implications for how widely this impacts the TCP stack.

24/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "^static void tcp_connect_init",
  "PathPrefixes": [
    "net/ipv4/tcp_output.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp_output.c=4092=static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)\n--\nnet/ipv4/tcp_output.c-4111-/* Do all connect socket setups that can be done AF independent. */\nnet/ipv4/tcp_output.c:4112:static void tcp_connect_init(struct sock *sk)\nnet/ipv4/tcp_output.c-4113-{\n"
}
25/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 19591
							output: 36
							thoughts: 13

Thoughts: 
Here's my take on those thoughts, tailored for an expert audience:

**Analyzing the Callers of `tcp_connect_init`**

Alright, let's dive in. I need to understand the call flow of `tcp_connect_init`. This function is fundamental to the connection establishment process, so knowing its callers is key to understanding network behavior, potential performance bottlenecks, and the overall state machine. I'm thinking about the various places this function might be invoked within the kernel.

I need to quickly recall the typical paths for a TCP connection attempt. We've got the standard `connect()` system call, which I'd expect to be the most common entry point. But, I know the kernel's more complex than that. Are there any internal, asynchronous connection attempts that also invoke `tcp_connect_init`? I need to think about features like connection re-establishment, connection tracking, NAT traversal – all could potentially touch this function.

Then there's the nuance within the protocol itself. Are there any specific conditions, perhaps related to different TCP options or error scenarios, that trigger a call to `tcp_connect_init`? It's essential to differentiate between normal connection attempts and those driven by specific edge cases or corner scenarios.

Basically, I need to form a mental map of all the call paths, the contexts in which they occur, and the specific reasons why the kernel needs to initialize a TCP connection. I should also consider how this relates to different network namespaces, security contexts, and other system-level configurations. I need to track down the callers, understand the reasons they call, and evaluate how efficiently this function is used.

26/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "tcp_connect_init",
  "PathPrefixes": [
    "net/ipv4/tcp_output.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp_output.c=4092=static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)\n--\nnet/ipv4/tcp_output.c-4111-/* Do all connect socket setups that can be done AF independent. */\nnet/ipv4/tcp_output.c:4112:static void tcp_connect_init(struct sock *sk)\nnet/ipv4/tcp_output.c-4113-{\n--\nnet/ipv4/tcp_output.c=4309=int tcp_connect(struct sock *sk)\n--\nnet/ipv4/tcp_output.c-4370-\nnet/ipv4/tcp_output.c:4371:\ttcp_connect_init(sk);\nnet/ipv4/tcp_output.c-4372-\n"
}
27/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 20207
							output: 23
							thoughts: 136

Thoughts: 
**Analyzing TCP Connection Initialization**

Okay, so `tcp_connect` kicks things off with a call to `tcp_connect_init`. From there, my focus narrows to `net/ipv4/tcp_minisocks.c` because I know that's a key area for connection management. Specifically, I'm zeroing in on `tcp_openreq_init_rwin`. My first question is always about scope: is this function exported or is it confined to the file? Ah, great, it's a `void tcp_openreq_init_rwin(struct request_sock *req, const struct sock *sk_listener, const struct dst_entry *dst);` function! Now that I know its signature, I need to understand its behavior. The crucial bit here is that it calls `tcp_req_window_clamp(tp, dst)`. Clearly, it's involved in setting up the receive window for a new connection request. I need to understand how the receive window is set up.

Now, my next logical step is to identify all the callers of `tcp_openreq_init_rwin`. Understanding how this function is used elsewhere will provide the context I need to fully grasp its role in the overall connection establishment process. Let's see who's calling this and understand the workflow.

28/2 2026/10/22 02:15 tool grepper
0m Args: 
{
  "Expression": "tcp_openreq_init_rwin"
}

Results: 
{
  "Output": "include/net/tcp.h=1866=static inline bool tcp_epollin_ready(const struct sock *sk, int target)\n--\ninclude/net/tcp.h-1877-\ninclude/net/tcp.h:1878:extern void tcp_openreq_init_rwin(struct request_sock *req,\ninclude/net/tcp.h-1879-\t\t\t\t  const struct sock *sk_listener,\n--\nnet/ipv4/tcp_input.c=7635=int tcp_conn_request(struct request_sock_ops *rsk_ops,\n--\nnet/ipv4/tcp_input.c-7774-\ttcp_rsk(req)-\u003esyn_tos = TCP_SKB_CB(skb)-\u003eip_dsfield;\nnet/ipv4/tcp_input.c:7775:\ttcp_openreq_init_rwin(req, sk, dst);\nnet/ipv4/tcp_input.c-7776-\tsk_rx_queue_set(req_to_sk(req), skb);\n--\nnet/ipv4/tcp_minisocks.c=412=void tcp_twsk_purge(struct list_head *net_exit_list)\n--\nnet/ipv4/tcp_minisocks.c-430- */\nnet/ipv4/tcp_minisocks.c:431:void tcp_openreq_init_rwin(struct request_sock *req,\nnet/ipv4/tcp_minisocks.c-432-\t\t\t   const struct sock *sk_listener,\n"
}
29/2 2026/10/22 02:15 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 21044
							output: 39
							thoughts: 1586

Thoughts: 
**Analyzing Symbol Coverage for TCP Window Clamp Changes**

Okay, so I'm looking at how to best target these changes for fuzzing coverage. The primary focus seems to be around `tcp_req_window_clamp`, which is a `static inline` function defined in `include/net/tcp.h`. The documentation clearly states that these inlined static functions don't have distinct symbol addresses in `vmlinux`, so we can't directly target them with symbol coverage filters. Instead, we need to identify non-static callers in `.c` files that *exercise* `tcp_req_window_clamp`. We want to avoid generic lifecycle wrappers.

The obvious candidates are those functions directly calling `tcp_req_window_clamp`, which are `tcp_openreq_init_rwin` (a non-static symbol, good!), `cookie_v4_check`, and `cookie_v6_check`. Perfect, they're all in different parts of the code base.

Then, there are other modified functions to consider, as they could also exercise the new clamping logic indirectly. That means `tcp_set_rcvbuf`, `do_tcp_setsockopt`, `tcp_disconnect`, and `tcp_connect_init` (which is inlined into `tcp_connect`, making it a potential candidate).

Now, the question is, how specific should we be? Do we list both `tcp_connect_init` and `tcp_connect`? While `tcp_connect_init` is specific, `tcp_connect` is ubiquitous, called on *every* TCP connection. Section 4 says to avoid ubiquitous hot-paths, and to target specific feature logic and entrypoints. While `tcp_connect_init` is static it is also specific, and `tcp_connect` is an entrypoint.

Given that, I want to clarify:

*   `tcp_set_rcvbuf` (modified directly): This is very specific, setting the receive buffer and, critically, calling `tcp_set_window_clamp` to enforce the clamp.
*   `do_tcp_setsockopt` (modified directly): This handles the `TCP_WINDOW_CLAMP` socket option.
*   `tcp_disconnect` (modified directly): Resets `window_clamp_user`.
*   `tcp_openreq_init_rwin`: Non-static, calls `tcp_req_window_clamp` directly.
*   `cookie_v4_check`, `cookie_v6_check`: Non-static, calls `tcp_req_window_clamp` directly.

The functions calling `tcp_req_window_clamp`, and directly modified functions such as `tcp_set_rcvbuf`, `do_tcp_setsockopt`, and `tcp_disconnect`, seem like the best targets.

30/2 2026/10/22 02:16 tool read-file
0m Args: 
{
  "File": "net/ipv4/tcp_output.c",
  "FirstLine": 4110,
  "LineCount": 80
}

Results: 
{
  "Contents": "4110:\t\n4111:\t/* Do all connect socket setups that can be done AF independent. */\n4112:\tstatic void tcp_connect_init(struct sock *sk)\n4113:\t{\n4114:\t\tconst struct dst_entry *dst = __sk_dst_get(sk);\n4115:\t\tstruct tcp_sock *tp = tcp_sk(sk);\n4116:\t\t__u8 rcv_wscale;\n4117:\t\tint full_space;\n4118:\t\tu16 user_mss;\n4119:\t\tu32 rcv_wnd;\n4120:\t\n4121:\t\t/* We'll fix this up when we get a response from the other end.\n4122:\t\t * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.\n4123:\t\t */\n4124:\t\ttp-\u003etcp_header_len = sizeof(struct tcphdr);\n4125:\t\tif (READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_timestamps))\n4126:\t\t\ttp-\u003etcp_header_len += TCPOLEN_TSTAMP_ALIGNED;\n4127:\t\n4128:\t\ttcp_ao_connect_init(sk);\n4129:\t\n4130:\t\t/* If user gave his TCP_MAXSEG, record it to clamp */\n4131:\t\tuser_mss = READ_ONCE(tp-\u003erx_opt.user_mss);\n4132:\t\tif (user_mss)\n4133:\t\t\ttp-\u003erx_opt.mss_clamp = user_mss;\n4134:\t\ttp-\u003emax_window = 0;\n4135:\t\ttcp_mtup_init(sk);\n4136:\t\ttcp_sync_mss(sk, dst_mtu(dst));\n4137:\t\n4138:\t\ttcp_ca_dst_init(sk, dst);\n4139:\t\n4140:\t\tif (!tp-\u003ewindow_clamp_user)\n4141:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, dst_metric(dst, RTAX_WINDOW));\n4142:\t\ttp-\u003eadvmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));\n4143:\t\n4144:\t\ttcp_initialize_rcv_mss(sk);\n4145:\t\n4146:\t\t/* limit the window selection if the user enforce a smaller rx buffer */\n4147:\t\tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\n4148:\t\t    (tp-\u003ewindow_clamp \u003e tcp_full_space(sk) || tp-\u003ewindow_clamp == 0))\n4149:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, tcp_full_space(sk));\n4150:\t\n4151:\t\trcv_wnd = tcp_rwnd_init_bpf(sk);\n4152:\t\tfull_space = tcp_full_space(sk);\n4153:\t\tif (rcv_wnd == 0)\n4154:\t\t\trcv_wnd = dst_metric(dst, RTAX_INITRWND);\n4155:\t\telse if (full_space \u003c (u64)rcv_wnd * tp-\u003eadvmss)\n4156:\t\t\tfull_space = min_t(u64, (u64)rcv_wnd * tp-\u003eadvmss, INT_MAX);\n4157:\t\n4158:\t\ttcp_select_initial_window(sk, full_space,\n4159:\t\t\t\t\t  tp-\u003eadvmss - (tp-\u003erx_opt.ts_recent_stamp ? tp-\u003etcp_header_len - sizeof(struct tcphdr) : 0),\n4160:\t\t\t\t\t  \u0026tp-\u003ercv_wnd,\n4161:\t\t\t\t\t  \u0026tp-\u003ewindow_clamp,\n4162:\t\t\t\t\t  READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_window_scaling),\n4163:\t\t\t\t\t  \u0026rcv_wscale,\n4164:\t\t\t\t\t  rcv_wnd);\n4165:\t\n4166:\t\ttp-\u003erx_opt.rcv_wscale = rcv_wscale;\n4167:\t\ttp-\u003ercv_ssthresh = tp-\u003ercv_wnd;\n4168:\t\n4169:\t\tWRITE_ONCE(sk-\u003esk_err, 0);\n4170:\t\tsock_reset_flag(sk, SOCK_DONE);\n4171:\t\ttp-\u003esnd_wnd = 0;\n4172:\t\ttcp_init_wl(tp, 0);\n4173:\t\ttcp_write_queue_purge(sk);\n4174:\t\tWRITE_ONCE(tp-\u003esnd_una, tp-\u003ewrite_seq);\n4175:\t\ttp-\u003esnd_sml = tp-\u003ewrite_seq;\n4176:\t\ttp-\u003esnd_up = tp-\u003ewrite_seq;\n4177:\t\tWRITE_ONCE(tp-\u003esnd_nxt, tp-\u003ewrite_seq);\n4178:\t\n4179:\t\tif (likely(!tp-\u003erepair))\n4180:\t\t\ttp-\u003ercv_nxt = 0;\n4181:\t\telse\n4182:\t\t\ttp-\u003ercv_tstamp = tcp_jiffies32;\n4183:\t\ttp-\u003ercv_wup = tp-\u003ercv_nxt;\n4184:\t\ttp-\u003ercv_mwnd_seq = tp-\u003ercv_nxt + tp-\u003ercv_wnd;\n4185:\t\tWRITE_ONCE(tp-\u003ecopied_seq, tp-\u003ercv_nxt);\n4186:\t\n4187:\t\tinet_csk(sk)-\u003eicsk_rto = tcp_timeout_init(sk);\n4188:\t\tWRITE_ONCE(inet_csk(sk)-\u003eicsk_retransmits, 0);\n4189:\t\ttcp_clear_retrans(tp);\n"
}
31/2 2026/10/22 02:16 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 24798
							output: 30
							thoughts: 636

Thoughts: 
**Analyzing TCP Window Clamp Management and Related Code**

Okay, so I'm looking at this code and trying to get a feel for the scope. `tcp_connect_init` is a fairly sizable function, about 80 lines. The compiler might or might not inline it, so listing it is a good starting point. I should probably also list the related functions, just to get a good overview. I'm thinking of `tcp_set_rcvbuf`, `tcp_set_window_clamp`, `do_tcp_setsockopt`, `tcp_openreq_init_rwin`, `cookie_v4_check`, `cookie_v6_check`, and `tcp_disconnect`.

Wait a second, is `tcp_set_window_clamp` even a good symbol to track? Seems a bit specific. Let's see... it's called within `tcp_set_rcvbuf` and `do_tcp_setsockopt`, specifically when handling `TCP_WINDOW_CLAMP`. It directly modifies `tp->window_clamp`, which is relevant for the window clamp.

Alright, so the patch modifies these functions: `tcp_set_rcvbuf`, `tcp_disconnect`, `do_tcp_setsockopt`, `tcp_openreq_init_rwin`, `tcp_connect_init`, `cookie_v4_check`, and `cookie_v6_check`. That's a focused set. These all seem related to TCP window clamp management, SYN handling, SYN cookie handling, socket options, and disconnection. Nothing here screams "hot path" like `kmalloc`, `kfree`, `copy_from_user`, or `page_fault`. Good.

Let's expand the scope a bit. What other files or configurations are involved?

Documentation tells me about `Documentation/networking/net_cachelines/tcp_sock.rst` - that's interesting. I should check that out. And there are some self-tests in `tools/testing/selftests/net/packetdrill/...`. I know the include headers would be `include/linux/tcp.h` and `include/net/tcp.h` – that's expected. For the C source files, I see `net/ipv4/syncookies.c`, `net/ipv4/tcp.c`, `net/ipv4/tcp_minisocks.c`, `net/ipv4/tcp_output.c`, and `net/ipv6/syncookies.c`.

Okay, what about config dependencies? I see that `INET` is required for the IPv4 TCP stack (`net/ipv4/tcp.c`, `net/ipv4/tcp_output.c`, `net/ipv4/tcp_minisocks.c`), and `IPV6` is required for IPv6 TCP support. `SYN_COOKIES` enables the compilation of `syncookies.c` in both IPv4 and IPv6.

I should verify that `net/ipv4/tcp.c` is always built when `INET` is enabled – let me quickly check the Makefile. Yep, it's there in the `obj-y` list. I will also check `net/ipv4/Makefile`.

32/2 2026/10/22 02:16 tool grepper
0m Args: 
{
  "Expression": "tcp.o",
  "PathPrefixes": [
    "net/ipv4/Makefile"
  ]
}

Results: 
{
  "Output": "net/ipv4/Makefile=6=obj-y     := route.o inetpeer.o protocol.o \\\n--\nnet/ipv4/Makefile-9-\t     inet_timewait_sock.o inet_connection_sock.o \\\nnet/ipv4/Makefile:10:\t     tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \\\nnet/ipv4/Makefile-11-\t     tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \\\nnet/ipv4/Makefile-12-\t     tcp_recovery.o tcp_ulp.o \\\nnet/ipv4/Makefile:13:\t     tcp_offload.o tcp_plb.o datagram.o raw.o udp.o \\\nnet/ipv4/Makefile-14-\t     udp_offload.o arp.o icmp.o devinet.o af_inet.o igmp.o \\\n--\nnet/ipv4/Makefile=51=obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o\nnet/ipv4/Makefile:52:obj-$(CONFIG_TCP_CONG_DCTCP) += tcp_dctcp.o\nnet/ipv4/Makefile-53-obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o\n--\nnet/ipv4/Makefile=55=obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o\nnet/ipv4/Makefile:56:obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o\nnet/ipv4/Makefile-57-obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o\n"
}
33/2 2026/10/22 02:16 llm patch-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 26592
							output: 173
							thoughts: 428

Thoughts: 
**Analysis of TCP Stack Code Paths**

Okay, let's break this down. First, I confirmed that `tcp.o`, `tcp_output.o`, and `tcp_minisocks.o` are indeed part of the `obj-y` list within `net/ipv4/Makefile`. That Makefile, as expected, is included when `CONFIG_INET=y`. And further validation: `obj-$(CONFIG_SYN_COOKIES) += syncookies.o` in both `net/ipv4/Makefile` *and* `net/ipv6/Makefile` corroborates the configuration dependencies for SYN cookies.

So, the core configurations at play here are: `INET`, `IPV6`, and `SYN_COOKIES`. No surprises there.

Next, I need to verify that the focus symbols are relevant, so I'll review those hot symbols:
*   `tcp_set_rcvbuf`: This one's linked to `setsockopt` usage with `SO_RCVBUF` or MPTCP which is expected.
*   `tcp_disconnect`: Tied to both `connect()` with `AF_UNSPEC` and disconnect calls, also as expected.
*   `do_tcp_setsockopt`: This is triggered by setsockopt() calls on TCP sockets specifically for SOL_TCP options.
*   `tcp_openreq_init_rwin`: Handshake related, initiated upon a SYN packet to a listener.
*   `tcp_connect_init`: Connected to the initiation of a TCP connection.
*   `cookie_v4_check`: Handles the IPv4 side of SYN cookies.
*   `cookie_v6_check`: Handles the IPv6 side of SYN cookies.

The key observation is that none of these symbols represent *ubiquitous* or performance-critical code paths, like allocations, locking primitives, or the core read/write operations. Rather, these functions directly address the *modified* code paths within the TCP stack related to our configs. The changes are all contained, and I am satisfied that all components are connected correctly.

That's it. Confirmed. Time to invoke `set-results`.

34/2 2026/10/22 02:16 tool set-results
0m Args: 
{
  "EnableConfigs": [
    "INET",
    "IPV6",
    "SYN_COOKIES"
  ],
  "FocusSymbols": [
    "tcp_set_rcvbuf",
    "tcp_disconnect",
    "do_tcp_setsockopt",
    "tcp_openreq_init_rwin",
    "tcp_connect_init",
    "cookie_v4_check",
    "cookie_v6_check"
  ],
  "Reasoning": "The patch modifies TCP window clamp handling across connection initialization, socket options (TCP_WINDOW_CLAMP, SO_RCVBUF), connection reset/disconnect, request sockets, and IPv4/IPv6 SYN cookies in core networking. This executable logic is directly reachable by userspace socket syscalls in standard virtualized environments.",
  "WorthFuzzing": true
}

Results: 
{
  "EnableConfigs": [
    "INET",
    "IPV6",
    "SYN_COOKIES"
  ],
  "FocusSymbols": [
    "tcp_set_rcvbuf",
    "tcp_disconnect",
    "do_tcp_setsockopt",
    "tcp_openreq_init_rwin",
    "tcp_connect_init",
    "cookie_v4_check",
    "cookie_v6_check"
  ],
  "Reasoning": "The patch modifies TCP window clamp handling across connection initialization, socket options (TCP_WINDOW_CLAMP, SO_RCVBUF), connection reset/disconnect, request sockets, and IPv4/IPv6 SYN cookies in core networking. This executable logic is directly reachable by userspace socket syscalls in standard virtualized environments.",
  "WorthFuzzing": true
}
35/1 2026/10/22 02:16 action If
1m Args: 
{
  "WorthFuzzing": true
}

Results: 
null
36/2 2026/10/22 02:16 agent kmsan-evaluator
1m Model: 
core

Args: 
null

Results: 
{
  "KMSANReasoning": "The patch series resolves an issue where setting SO_RCVBUF unintentionally overwrote `tp-\u003ewindow_clamp`, causing TCP window calculations on connect, listen, or SYN cookies to mistake receive buffer adjustments for user-configured window clamps. To fix this, it adds `tp-\u003ewindow_clamp_user` to `struct tcp_sock` to track whether `TCP_WINDOW_CLAMP` was explicitly set by the user.\n\nKMSAN applicability assessment:\n1. Memory initialization: Sockets (`struct tcp_sock`) are allocated with `__GFP_ZERO` via `sk_alloc()` and cloned via `sock_copy()` in `sk_clone()`. The new field `window_clamp_user` is initialized to zero upon allocation, cleared on `tcp_disconnect()`, and set explicitly in `do_tcp_setsockopt()`. It is never read uninitialized.\n2. Kernel-to-user info leaks: The patch does not expose any new fields or structures to user space; `window_clamp_user` is an internal TCP state variable not copied to user space.\n3. Buffer parsing and length handling: The change modifies TCP window clamp calculations and route metric lookups (`tcp_req_window_clamp()`). No packet buffer slicing, payload accesses, or memory copying operations are altered in ways that could expose uninitialized buffer memory.\n\nBecause no uninitialized memory reads or information leak risks are introduced or exposed, dedicated KMSAN fuzzing is not required. Any functional or concurrency issues are sufficiently covered by packetdrill tests, KASAN, and KCSAN.",
  "NeedsKMSAN": false
}

Instruction: 
You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.

CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
  a comprehensive suite of debugging tools and sanitizers, including KASAN
  (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
  (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
  or page allocations) and kernel-to-user memory info-leaks.

Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.

Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.

Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
   attributes, ioctl output arguments, socket options, or BPF buffers) where fields
   or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
   or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
   could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
   uninitialized bytes of existing buffers.

Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
  dereferences, locking deadlocks, or use-after-free bugs (these are already caught
  by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
  or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Prompt: 
Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 3ad7cca995e47c2dfe2edb33638b17fb297e71c3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Oct 22 02:14:36 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/networking/net_cachelines/tcp_sock.rst b/Documentation/networking/net_cachelines/tcp_sock.rst
index 103328dc409e4..f317c7154d26f 100644
--- a/Documentation/networking/net_cachelines/tcp_sock.rst
+++ b/Documentation/networking/net_cachelines/tcp_sock.rst
@@ -152,6 +152,7 @@ u32                           urg_seq
 unsigned_int                  keepalive_time
 unsigned_int                  keepalive_intvl
 int                           linger2
+u32                           window_clamp_user
 u8                            bpf_sock_ops_cb_flags
 u8:1                          bpf_chg_cc_inprogress
 u16                           timeout_rehash
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index e4d1720f49f08..4f28fa6c4f4ea 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -474,6 +474,7 @@ struct tcp_sock {
 	unsigned int		keepalive_intvl;  /* time interval between keep alive probes */
 
 	int			linger2;
+	u32	window_clamp_user; /* TCP_WINDOW_CLAMP set by the user, 0 if none */
 
 
 /* Sock_ops bpf program related variables */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0265c27a5fd77..35b64fffd74bc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1879,6 +1879,20 @@ extern void tcp_openreq_init_rwin(struct request_sock *req,
 				  const struct sock *sk_listener,
 				  const struct dst_entry *dst);
 
+/* Window clamp for a request socket of listener @tp: the listener's clamp
+ * if the user set one with TCP_WINDOW_CLAMP, else the route window metric.
+ * The SYN-ACK and the SYN cookie paths must make the same choice, or the
+ * child's window scale would not match the one sent in the SYN-ACK.
+ * The listener is not locked here.
+ */
+static inline u32 tcp_req_window_clamp(const struct tcp_sock *tp,
+				       const struct dst_entry *dst)
+{
+	if (READ_ONCE(tp->window_clamp_user))
+		return READ_ONCE(tp->window_clamp);
+	return dst_metric(dst, RTAX_WINDOW);
+}
+
 void tcp_enter_memory_pressure(struct sock *sk);
 void tcp_leave_memory_pressure(struct sock *sk);
 
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 73e1297681847..6e78efbdc315f 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -472,8 +472,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	}
 
 	/* Try to redo what tcp_v4_send_synack did. */
-	req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :
-				dst_metric(&rt->dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, &rt->dst);
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	full_space = tcp_full_space(sk);
 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 99d7237a623d8..64465bc257d18 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1859,7 +1859,15 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
 
 void tcp_set_rcvbuf(struct sock *sk, int val)
 {
-	tcp_set_window_clamp(sk, tcp_win_from_space(sk, val));
+	u32 user_clamp = tcp_sk(sk)->window_clamp_user;
+	int win = tcp_win_from_space(sk, val);
+
+	/* window_clamp follows the receive buffer, but never goes above a
+	 * clamp the user set with TCP_WINDOW_CLAMP.
+	 */
+	if (user_clamp)
+		win = min_t(u32, win, user_clamp);
+	tcp_set_window_clamp(sk, win);
 }
 
 #ifdef CONFIG_MMU
@@ -3429,6 +3437,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->is_cwnd_limited = 0;
 	tp->max_packets_out = 0;
 	tp->window_clamp = 0;
+	WRITE_ONCE(tp->window_clamp_user, 0);
 	tp->delivered = 0;
 	tp->delivered_ce = 0;
 	tp->accecn_fail_mode = 0;
@@ -4058,6 +4067,9 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 
 	case TCP_WINDOW_CLAMP:
 		err = tcp_set_window_clamp(sk, val);
+		if (!err)
+			WRITE_ONCE(tp->window_clamp_user,
+				   val ? tp->window_clamp : 0);
 		break;
 
 	case TCP_QUICKACK:
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 0ddfd5af6e58f..c17dc5c464802 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -435,15 +435,13 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 	struct inet_request_sock *ireq = inet_rsk(req);
 	const struct tcp_sock *tp = tcp_sk(sk_listener);
 	int full_space = tcp_full_space(sk_listener);
-	u32 window_clamp;
 	__u8 rcv_wscale;
 	u32 rcv_wnd;
 	int mss;
 
 	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
-	window_clamp = READ_ONCE(tp->window_clamp);
 	/* Set this up on the first call only */
-	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, dst);
 
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c8865205cdc8b..21b4ae303dd63 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -4137,7 +4137,7 @@ static void tcp_connect_init(struct sock *sk)
 
 	tcp_ca_dst_init(sk, dst);
 
-	if (!tp->window_clamp)
+	if (!tp->window_clamp_user)
 		WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
 	tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index b581cb1ee2e8a..d7d61f8d25e55 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -254,7 +254,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		}
 	}
 
-	req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);
+	req->rsk_window_clamp = tcp_req_window_clamp(tp, dst);
 	/* limit the window selection if the user enforce a smaller rx buffer */
 	full_space = tcp_full_space(sk);
 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
diff --git a/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
new file mode 100644
index 0000000000000..b297294ed1659
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_FASTOPEN_CONNECT defers the SYN until the first write(); between
+// connect() and that write the socket is in TCP_SYN_SENT. SO_RCVBUF applied
+// in that gap must not defeat the route "window" metric on the deferred SYN.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_fastopen=5
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_NO_COOKIE, [1], 4) = 0
+   +0 connect(3, ..., ...) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 write(3, ..., 1) = 1
+
+// The deferred SYN (carrying 1 byte of data) must advertise the route
+// clamped window and window scale 0 (not win 65535, wscale 5).
+   +0 > S 0:1(1) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
new file mode 100644
index 0000000000000..7ec7f14d8e896
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// Setting SO_RCVBUF before connect() must not defeat the route "window"
+// metric on the SYN.
+//
+// The route to the peer carries "window 4096" (RTAX_WINDOW). With SO_RCVBUF
+// also set before connect(), the SYN the kernel sends must still advertise
+// the small, route-clamped receive window and a window scale of 0 (the
+// window scale option is sent, with a shift of 0).
+//
+// Since commit b025461303d8 ("tcp: update window_clamp when SO_RCVBUF is
+// set"), setsockopt(SO_RCVBUF) wrote tp->window_clamp while the socket was
+// still in TCP_CLOSE. tcp_connect_init() then treated that as a user clamp
+// and skipped RTAX_WINDOW, so the SYN carried win 65535, wscale 5 instead.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN must advertise the route-clamped window and window scale 0.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
new file mode 100644
index 0000000000000..ed20a75fa9aab
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: SO_RCVBUF set on a listener must not defeat the route
+// "window" metric on the SYN-ACK, and the child must use the window scale
+// that the SYN-ACK advertised.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
new file mode 100644
index 0000000000000..e26f78704abcd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v4_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
new file mode 100644
index 0000000000000..8b5dd71d765fe
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v6_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv6
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip -6 route replace fd3d:fa7b:d17d::1 via fd3d:0a0b:17d6:8888::1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
new file mode 100644
index 0000000000000..08ef005bf99a1
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// After the handshake, tcp_init_buffer_space() lowers window_clamp to the
+// receive space. A later, larger SO_RCVBUF must raise window_clamp again,
+// but only up to the clamp the user set with TCP_WINDOW_CLAMP.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [40000], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+   +0 > S 0:0(0) <...>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
+
+// The small receive buffer keeps window_clamp below the user's clamp:
+// 8192 (tcp_full_space()) minus the one segment (advmss 1460) that
+// tcp_init_buffer_space() reserves.
+   +0 getsockopt(3, SOL_TCP, 10, [6732], [4]) = 0
+
+// A larger SO_RCVBUF raises it again, up to the user's clamp.
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [212992], 4) = 0
+   +0 getsockopt(3, SOL_TCP, 10, [40000], [4]) = 0
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
new file mode 100644
index 0000000000000..458f2f313c7dd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_WINDOW_CLAMP set back to 0 on an unconnected socket removes the
+// user's clamp: a later SO_RCVBUF must then not stop the route "window"
+// metric from being applied on the SYN.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [0], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// No user clamp is left, so the SYN advertises the route window.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
new file mode 100644
index 0000000000000..69a05959e42eb
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+// A window clamp the user set with setsockopt(TCP_WINDOW_CLAMP) must be
+// honoured on the SYN even when SO_RCVBUF is set afterwards on the still
+// unconnected socket: SO_RCVBUF must not raise window_clamp above the
+// user's clamp, and the route "window" metric must not replace it either.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN advertises the user's clamp (win 16060), not the route window
+// (2920) and not the SO_RCVBUF-derived full window.
+   +0 > S 0:0(0) win 16060 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
new file mode 100644
index 0000000000000..f7e7ddb5000d3
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: a TCP_WINDOW_CLAMP set on a listener must be honoured on
+// the SYN-ACK even when SO_RCVBUF is set afterwards on the listener, and
+// the route "window" metric must not replace it.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+// The SYN-ACK advertises the user's clamp, not the route window and not
+// the SO_RCVBUF-derived full window.
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 15928 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%

37/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 9987
							output: 63
							thoughts: 97

Thoughts: 
Okay, here's my breakdown of what I'm thinking, rendered as a first-person expert summary:

**Analyzing the TCP Window Clamping Patch Series**

Right, let's dive into this patch series. My initial thought is to understand the scope of the modifications. What's actually changing in the TCP window clamping logic? The description mentions adding a new field, `window_clamp_user` (a `u32`), to the `struct tcp_sock`. Okay, that's the core of it, at least on the surface.

Now, I need to understand the implications of this new field. I'm immediately wondering about the allocation strategy for `struct tcp_sock`. How is it allocated? Is it on the stack, dynamically from the heap, perhaps with some kind of slab allocator? Understanding the allocation is critical to assess the potential impact of this change across different network scenarios and memory management behaviors in the kernel. This also helps with understanding lock contention and performance.

Time to consult the source. Let's start by finding where `tcp_sock` is allocated and initialized. I'm going to fire up `grepper` and search for allocations of the `tcp_sock` structure. That should give me a good starting point to trace the usage and ensure I understand the impact of any changes to this structure. This will provide a broader context around how this new field is managed and used within the larger TCP stack.

38/3 2026/10/22 02:16 tool grepper
0m Args: 
{
  "Expression": "tcp_sock_destructor|tcp_alloc_socket|tcp_create|inet_csk_clone_lock|inet_twsk_alloc|tcp_sk_init",
  "PathPrefixes": [
    "net/ipv4"
  ]
}

Results: 
{
  "Output": "net/ipv4/inet_connection_sock.c=1185=static void inet_clone_ulp(const struct request_sock *req, struct sock *newsk,\n--\nnet/ipv4/inet_connection_sock.c-1196-/**\nnet/ipv4/inet_connection_sock.c:1197: *\tinet_csk_clone_lock - clone an inet socket, and lock its clone\nnet/ipv4/inet_connection_sock.c-1198- *\t@sk: the socket to clone\n--\nnet/ipv4/inet_connection_sock.c-1203- */\nnet/ipv4/inet_connection_sock.c:1204:struct sock *inet_csk_clone_lock(const struct sock *sk,\nnet/ipv4/inet_connection_sock.c-1205-\t\t\t\t const struct request_sock *req,\n--\nnet/ipv4/inet_connection_sock.c=1294=void inet_csk_prepare_for_destroy_sock(struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c-1302-/* This function allows to force a closure of a socket after the call to\nnet/ipv4/inet_connection_sock.c:1303: * tcp_create_openreq_child().\nnet/ipv4/inet_connection_sock.c-1304- */\n--\nnet/ipv4/inet_timewait_sock.c=163=static void tw_timer_handler(struct timer_list *t)\n--\nnet/ipv4/inet_timewait_sock.c-169-\nnet/ipv4/inet_timewait_sock.c:170:struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,\nnet/ipv4/inet_timewait_sock.c-171-\t\t\t\t\t   struct inet_timewait_death_row *dr,\n--\nnet/ipv4/tcp_ao.c=918=void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb,\n--\nnet/ipv4/tcp_ao.c-927-\t/* treq-\u003eaf_specific is used to perform TCP_AO lookup\nnet/ipv4/tcp_ao.c:928:\t * in tcp_create_openreq_child().\nnet/ipv4/tcp_ao.c-929-\t */\n--\nnet/ipv4/tcp_fastopen.c=257=void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv4/tcp_fastopen.c-268-\ttcp_cleanup_skb(skb);\nnet/ipv4/tcp_fastopen.c:269:\t/* segs_in has been initialized to 1 in tcp_create_openreq_child().\nnet/ipv4/tcp_fastopen.c-270-\t * Hence, reset segs_in to 0 before calling tcp_segs_in()\n--\nnet/ipv4/tcp_ipv4.c=494=int tcp_v4_err(struct sk_buff *skb, u32 info)\n--\nnet/ipv4/tcp_ipv4.c-555-\ttp = tcp_sk(sk);\nnet/ipv4/tcp_ipv4.c:556:\t/* XXX (TFO) - tp-\u003esnd_una should be ISN (tcp_create_openreq_child() */\nnet/ipv4/tcp_ipv4.c-557-\tfastopen = rcu_dereference(tp-\u003efastopen_rsk);\n--\nnet/ipv4/tcp_ipv4.c=1677=struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,\n--\nnet/ipv4/tcp_ipv4.c-1699-\nnet/ipv4/tcp_ipv4.c:1700:\tnewsk = tcp_create_openreq_child(sk, req, skb);\nnet/ipv4/tcp_ipv4.c-1701-\tif (!newsk)\n--\nnet/ipv4/tcp_ipv4.c=3410=static void __net_init tcp_set_hashinfo(struct net *net)\n--\nnet/ipv4/tcp_ipv4.c-3439-\nnet/ipv4/tcp_ipv4.c:3440:static int __net_init tcp_sk_init(struct net *net)\nnet/ipv4/tcp_ipv4.c-3441-{\n--\nnet/ipv4/tcp_ipv4.c=3573=static struct pernet_operations __net_initdata tcp_sk_ops = {\nnet/ipv4/tcp_ipv4.c:3574:       .init\t   = tcp_sk_init,\nnet/ipv4/tcp_ipv4.c-3575-       .exit\t   = tcp_sk_exit,\n--\nnet/ipv4/tcp_minisocks.c=326=void tcp_time_wait(struct sock *sk, int state, int timeo)\n--\nnet/ipv4/tcp_minisocks.c-332-\nnet/ipv4/tcp_minisocks.c:333:\ttw = inet_twsk_alloc(sk, \u0026net-\u003eipv4.tcp_death_row, state);\nnet/ipv4/tcp_minisocks.c-334-\n--\nnet/ipv4/tcp_minisocks.c=523=static void smc_check_reset_syn_req(const struct tcp_sock *oldtp,\n--\nnet/ipv4/tcp_minisocks.c-543- */\nnet/ipv4/tcp_minisocks.c:544:struct sock *tcp_create_openreq_child(const struct sock *sk,\nnet/ipv4/tcp_minisocks.c-545-\t\t\t\t      struct request_sock *req,\n--\nnet/ipv4/tcp_minisocks.c-547-{\nnet/ipv4/tcp_minisocks.c:548:\tstruct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);\nnet/ipv4/tcp_minisocks.c-549-\tconst struct inet_request_sock *ireq = inet_rsk(req);\n"
}
39/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 12041
							output: 33
							thoughts: 73

Thoughts: 
Here's my understanding of how a `struct tcp_sock` is allocated on socket creation, as I see it:

**Tracing TCP Socket Allocation**

Okay, so I'm trying to follow the memory allocation path for a `struct tcp_sock` when a new socket is created. My current thinking is: We start with `sk_alloc()`. That should be the entry point. Within that, I see `sk_prot_alloc()` called. And from experience, that's almost certainly going to involve `kmem_cache_alloc_node`, probably with some zeroing or `memset` thrown in there to initialize the allocated memory. I need to be sure though, so I'll check the source of `sk_alloc` located in `net/core/sock.c` to verify this sequence of events.

40/3 2026/10/22 02:16 tool grepper
0m Args: 
{
  "Expression": "sk_prot_alloc",
  "PathPrefixes": [
    "net/core/sock.c"
  ]
}

Results: 
{
  "Output": "net/core/sock.c=2210=static void sock_copy(struct sock *nsk, const struct sock *osk)\n--\nnet/core/sock.c-2229-\t\t      prot-\u003eobj_size - offsetof(struct sock, sk_dontcopy_end),\nnet/core/sock.c:2230:\t\t      /* alloc is larger than struct, see sk_prot_alloc() */);\nnet/core/sock.c-2231-\n--\nnet/core/sock.c-2237-\nnet/core/sock.c:2238:static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,\nnet/core/sock.c-2239-\t\tint family)\n--\nnet/core/sock.c=2303=struct sock *sk_alloc(struct net *net, int family, gfp_t priority,\n--\nnet/core/sock.c-2307-\nnet/core/sock.c:2308:\tsk = sk_prot_alloc(prot, priority | __GFP_ZERO, family);\nnet/core/sock.c-2309-\tif (sk) {\n--\nnet/core/sock.c=2480=struct sock *sk_clone(const struct sock *sk, const gfp_t priority,\n--\nnet/core/sock.c-2487-\nnet/core/sock.c:2488:\tnewsk = sk_prot_alloc(prot, priority, sk-\u003esk_family);\nnet/core/sock.c-2489-\tif (!newsk)\n"
}
41/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 12730
							output: 35
							thoughts: 108

Thoughts: 
**Analyzing TCP Socket Cloning and Window Clamping**

Okay, so I'm looking at how TCP sockets are handled, specifically focusing on the cloning process. My initial thought is about memory allocation. I see this `sk_prot_alloc` function being called, allocating the new socket (`sk`) with the specified protocol (`prot`), priority, and zeroing the memory. That makes sense; it's the basic setup for a new socket.

Then, during the cloning operation itself – diving into `sk_clone` – the key part is `sock_copy`. This function is pivotal as it's the mechanism for copying socket data. The interesting detail lies in the segmenting.  It makes a copy, but also *clears* certain data between `sk_dontcopy_begin` and `sk_dontcopy_end`. This is important for preventing unintended data sharing, or potential leaks of sensitive data from the original socket. It also tells me I need to understand what these bounds mean.

Now, my mind shifts to `window_clamp_user`. I need to figure out precisely where this variable, which is crucial for managing the TCP receive window from a user perspective, resides within the `tcp_sock` structure. I'm going to look at the `include/linux/tcp.h` header file. It's almost certain it's in there, and given my experience, I'll start looking around line 474. It's likely that it will be adjacent to related window management variables. Let's see what's there...

42/3 2026/10/22 02:16 tool read-file
0m Args: 
{
  "File": "include/linux/tcp.h",
  "FirstLine": 465,
  "LineCount": 35
}

Results: 
{
  "Contents": " 465:\t\t\t\t\t * SYN/SYN-ACK and recurring timeouts.\n 466:\t\t\t\t\t */\n 467:\t\tu16\ttotal_rto_recoveries;\t/* Total number of RTO recoveries,\n 468:\t\t\t\t\t\t * including any unfinished recovery.\n 469:\t\t\t\t\t\t */\n 470:\t\tu32\ttotal_rto_time;\t/* ms spent in (completed) RTO recoveries. */\n 471:\t\n 472:\t\tu32\turg_seq;\t/* Seq of received urgent pointer */\n 473:\t\tunsigned int\t\tkeepalive_time;\t  /* time before keep alive takes place */\n 474:\t\tunsigned int\t\tkeepalive_intvl;  /* time interval between keep alive probes */\n 475:\t\n 476:\t\tint\t\t\tlinger2;\n 477:\t\tu32\twindow_clamp_user; /* TCP_WINDOW_CLAMP set by the user, 0 if none */\n 478:\t\n 479:\t\n 480:\t/* Sock_ops bpf program related variables */\n 481:\t#ifdef CONFIG_BPF\n 482:\t\tu8\tbpf_sock_ops_cb_flags;  /* Control calling BPF programs\n 483:\t\t\t\t\t\t * values defined in uapi/linux/tcp.h\n 484:\t\t\t\t\t\t */\n 485:\t\tu8\tbpf_chg_cc_inprogress:1; /* In the middle of\n 486:\t\t\t\t\t\t  * bpf_setsockopt(TCP_CONGESTION),\n 487:\t\t\t\t\t\t  * it is to avoid the bpf_tcp_cc-\u003einit()\n 488:\t\t\t\t\t\t  * to recur itself by calling\n 489:\t\t\t\t\t\t  * bpf_setsockopt(TCP_CONGESTION, \"itself\").\n 490:\t\t\t\t\t\t  */\n 491:\t#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP-\u003ebpf_sock_ops_cb_flags \u0026 ARG)\n 492:\t#else\n 493:\t#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0\n 494:\t#endif\n 495:\t\n 496:\t\tu16 timeout_rehash;\t/* Timeout-triggered rehash attempts */\n 497:\t\n 498:\t\tu32 rcv_ooopack; /* Received out-of-order packets, for tcpinfo */\n 499:\t\n"
}
43/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 13829
							output: 40
							thoughts: 68

Thoughts: 
Here's my thought process, as it stands:

**Examining TCP Socket Creation Behavior**

Okay, so I'm trying to figure out something specific about how TCP sockets are created and handled, specifically the interaction of `window_clamp_user` during child socket instantiation. The question on my mind is: when a child socket is spawned, does the `window_clamp_user` value get properly copied over? I need to clarify the specifics of this replication or lack thereof.

Therefore, my next step is to examine the code responsible for creating child sockets. I need to dive into `tcp_create_openreq_child`. Specifically, I will look at how the child socket is initialized within that function to confirm my assumption, and to verify how `window_clamp_user` is handled in this child creation context. The path to this function is `net/ipv4/tcp_minisocks.c`, so I'll start by reading that code.

44/3 2026/10/22 02:16 tool read-file
0m Args: 
{
  "File": "net/ipv4/tcp_minisocks.c",
  "FirstLine": 544,
  "LineCount": 80
}

Results: 
{
  "Contents": " 544:\tstruct sock *tcp_create_openreq_child(const struct sock *sk,\n 545:\t\t\t\t\t      struct request_sock *req,\n 546:\t\t\t\t\t      struct sk_buff *skb)\n 547:\t{\n 548:\t\tstruct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);\n 549:\t\tconst struct inet_request_sock *ireq = inet_rsk(req);\n 550:\t\tstruct tcp_request_sock *treq = tcp_rsk(req);\n 551:\t\tstruct inet_connection_sock *newicsk;\n 552:\t\tconst struct tcp_sock *oldtp;\n 553:\t\tstruct tcp_sock *newtp;\n 554:\t\tu32 seq;\n 555:\t\n 556:\t\tif (!newsk)\n 557:\t\t\treturn NULL;\n 558:\t\n 559:\t\tnewicsk = inet_csk(newsk);\n 560:\t\tnewtp = tcp_sk(newsk);\n 561:\t\toldtp = tcp_sk(sk);\n 562:\t\n 563:\t\tsmc_check_reset_syn_req(oldtp, req, newtp);\n 564:\t\n 565:\t\t/* Now setup tcp_sock */\n 566:\t\tnewtp-\u003epred_flags = 0;\n 567:\t\n 568:\t\tseq = treq-\u003ercv_isn + 1;\n 569:\t\tnewtp-\u003ercv_wup = seq;\n 570:\t\tWRITE_ONCE(newtp-\u003ecopied_seq, seq);\n 571:\t\tWRITE_ONCE(newtp-\u003ercv_nxt, seq);\n 572:\t\tnewtp-\u003esegs_in = 1;\n 573:\t\n 574:\t\tseq = treq-\u003esnt_isn + 1;\n 575:\t\tnewtp-\u003esnd_sml = newtp-\u003esnd_una = seq;\n 576:\t\tWRITE_ONCE(newtp-\u003esnd_nxt, seq);\n 577:\t\tnewtp-\u003esnd_up = seq;\n 578:\t\n 579:\t\tINIT_LIST_HEAD(\u0026newtp-\u003etsq_node);\n 580:\t\tINIT_LIST_HEAD(\u0026newtp-\u003etsorted_sent_queue);\n 581:\t\n 582:\t\ttcp_init_wl(newtp, treq-\u003ercv_isn);\n 583:\t\n 584:\t\tminmax_reset(\u0026newtp-\u003ertt_min, tcp_jiffies32, ~0U);\n 585:\t\tnewicsk-\u003eicsk_ack.lrcvtime = tcp_jiffies32;\n 586:\t\n 587:\t\tnewtp-\u003elsndtime = tcp_jiffies32;\n 588:\t\tnewsk-\u003esk_txhash = READ_ONCE(treq-\u003etxhash);\n 589:\t\tnewtp-\u003etotal_retrans = req-\u003enum_retrans;\n 590:\t\n 591:\t\ttcp_init_xmit_timers(newsk);\n 592:\t\tWRITE_ONCE(newtp-\u003ewrite_seq, newtp-\u003epushed_seq = treq-\u003esnt_isn + 1);\n 593:\t\n 594:\t\tif (sock_flag(newsk, SOCK_KEEPOPEN))\n 595:\t\t\ttcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));\n 596:\t\n 597:\t\tnewtp-\u003erx_opt.tstamp_ok = ireq-\u003etstamp_ok;\n 598:\t\tnewtp-\u003erx_opt.sack_ok = ireq-\u003esack_ok;\n 599:\t\tnewtp-\u003ewindow_clamp = req-\u003ersk_window_clamp;\n 600:\t\tnewtp-\u003ercv_ssthresh = req-\u003ersk_rcv_wnd;\n 601:\t\tnewtp-\u003ercv_wnd = req-\u003ersk_rcv_wnd;\n 602:\t\tnewtp-\u003ercv_mwnd_seq = newtp-\u003ercv_wup + req-\u003ersk_rcv_wnd;\n 603:\t\tnewtp-\u003erx_opt.wscale_ok = ireq-\u003ewscale_ok;\n 604:\t\tif (newtp-\u003erx_opt.wscale_ok) {\n 605:\t\t\tnewtp-\u003erx_opt.snd_wscale = ireq-\u003esnd_wscale;\n 606:\t\t\tnewtp-\u003erx_opt.rcv_wscale = ireq-\u003ercv_wscale;\n 607:\t\t} else {\n 608:\t\t\tnewtp-\u003erx_opt.snd_wscale = newtp-\u003erx_opt.rcv_wscale = 0;\n 609:\t\t\tnewtp-\u003ewindow_clamp = min(newtp-\u003ewindow_clamp, 65535U);\n 610:\t\t}\n 611:\t\tnewtp-\u003esnd_wnd = ntohs(tcp_hdr(skb)-\u003ewindow) \u003c\u003c newtp-\u003erx_opt.snd_wscale;\n 612:\t\tnewtp-\u003emax_window = newtp-\u003esnd_wnd;\n 613:\t\n 614:\t\tif (newtp-\u003erx_opt.tstamp_ok) {\n 615:\t\t\tnewtp-\u003etcp_usec_ts = treq-\u003ereq_usec_ts;\n 616:\t\t\tnewtp-\u003erx_opt.ts_recent = req-\u003ets_recent;\n 617:\t\t\tnewtp-\u003erx_opt.ts_recent_stamp = ktime_get_seconds();\n 618:\t\t\tnewtp-\u003etcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;\n 619:\t\t} else {\n 620:\t\t\tnewtp-\u003etcp_usec_ts = 0;\n 621:\t\t\tnewtp-\u003erx_opt.ts_recent_stamp = 0;\n 622:\t\t\tnewtp-\u003etcp_header_len = sizeof(struct tcphdr);\n 623:\t\t}\n"
}
45/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 15709
							output: 38
							thoughts: 89

Thoughts: 
Okay, here's my interpretation of this scenario, focusing on the key technical considerations:

**Investigating a Potential Data Copying Issue in the Kernel's Network Stack**

Right, so I'm looking at `inet_csk_clone_lock`. My immediate thought is that it's handling the cloning of a socket, `sk`, into a new socket, `newsk`. The code seems pretty straightforward at face value, copying the data. But a potential gotcha pops into my head. I'm specifically concerned about the scope of the copy.

I'm zeroing in on `window_clamp_user`. I know that particular variable resides within `struct tcp_sock`, which, as I recall, sits *beyond* the scope of `struct inet_connection_sock`. My crucial question is: Does this `inet_csk_clone_lock` function copy the *entire* `struct tcp_sock` structure? Or does it potentially stop at the boundary of `inet_connection_sock`, leading to incomplete cloning of the TCP-specific data? It's a key question, and to resolve it, I'm going to jump straight into the code for `inet_csk_clone_lock`. I need to confirm whether a deep copy occurs, and if not, I'll need to understand how the relevant data is handled to prevent a bug.

46/3 2026/10/22 02:16 tool grepper
0m Args: 
{
  "Expression": "sk_clone_lock",
  "PathPrefixes": [
    "net/ipv4/inet_connection_sock.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/inet_connection_sock.c=1185=static void inet_clone_ulp(const struct request_sock *req, struct sock *newsk,\n--\nnet/ipv4/inet_connection_sock.c-1196-/**\nnet/ipv4/inet_connection_sock.c:1197: *\tinet_csk_clone_lock - clone an inet socket, and lock its clone\nnet/ipv4/inet_connection_sock.c-1198- *\t@sk: the socket to clone\n--\nnet/ipv4/inet_connection_sock.c-1203- */\nnet/ipv4/inet_connection_sock.c:1204:struct sock *inet_csk_clone_lock(const struct sock *sk,\nnet/ipv4/inet_connection_sock.c-1205-\t\t\t\t const struct request_sock *req,\n--\nnet/ipv4/inet_connection_sock.c-1207-{\nnet/ipv4/inet_connection_sock.c:1208:\tstruct sock *newsk = sk_clone_lock(sk, priority);\nnet/ipv4/inet_connection_sock.c-1209-\tstruct inet_connection_sock *newicsk;\n--\nnet/ipv4/inet_connection_sock.c=1305=void inet_csk_prepare_forced_close(struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c-1307-{\nnet/ipv4/inet_connection_sock.c:1308:\t/* sk_clone_lock locked the socket and set refcnt to 2 */\nnet/ipv4/inet_connection_sock.c-1309-\tbh_unlock_sock(sk);\n"
}
47/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 16566
							output: 33
							thoughts: 35

Thoughts: 
Here's my summary, as though I'm thinking through this process:

**Diving into Socket Cloning**

Okay, so I see a function called `sk_clone_lock`. My immediate thought is, "Where does this fit into the bigger picture? What's it doing with the socket?" It's clear from the name that it's related to cloning, likely involving some kind of lock. So, the logical next step is to examine the source code of `sk_clone_lock`, specifically in `net/core/sock.c`. I need to understand the relationship between this locking function and the `sk_clone` function it calls, and figure out the exact mechanisms and timing surrounding the socket cloning process, in a networking context. Let's see what's going on under the hood.

48/3 2026/10/22 02:16 tool grepper
0m Args: 
{
  "Expression": "sk_clone_lock",
  "PathPrefixes": [
    "net/core/sock.c"
  ]
}

Results: 
{
  "Output": "net/core/sock.c=2210=static void sock_copy(struct sock *nsk, const struct sock *osk)\n--\nnet/core/sock.c-2218-\t * we must check if sk_tx_queue_clear() is called after\nnet/core/sock.c:2219:\t * sock_copy() in sk_clone_lock().\nnet/core/sock.c-2220-\t */\n"
}
49/3 2026/10/22 02:16 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 16924
							output: 36
							thoughts: 19

Thoughts: 
Okay, let's dive into this. Here's my take on understanding this `sock_copy` function:

**Analyzing `sock_copy` in `net/core/sock.c`**

Alright, I'm heading into `net/core/sock.c` to examine `sock_copy`. Right off the bat, I know this function is going to be crucial for data movement within the network stack, likely involving copying data between kernel buffers and user-space buffers or within the kernel itself. Given its name, "copy" is the key element, and the "sock" prefix suggests this will be socket-related. I'll need to pay close attention to the source and destination buffers, potential locking mechanisms used for concurrency, and error handling. I anticipate it'll be a fairly low-level function, perhaps utilizing `memcpy` or similar memory transfer routines under the hood. I'm looking for where this function fits into the overall socket processing flow – is it used during `recv`, `send`, or both? What are the calling contexts? Are there any special considerations for different socket types (TCP, UDP, etc.)? I'll probably also be looking for any uses of `skb` (socket buffer) because that is a key data structure in the kernel for network data. I'll be particularly interested in understanding how it handles fragmented data or partial copies. Ultimately, my goal is to grasp its role in transferring data and handling the nuances of memory management and concurrency within the kernel's network stack. Time to get started!

50/3 2026/10/22 02:17 tool read-file
0m Args: 
{
  "File": "net/core/sock.c",
  "FirstLine": 2210,
  "LineCount": 40
}

Results: 
{
  "Contents": "2210:\tstatic void sock_copy(struct sock *nsk, const struct sock *osk)\n2211:\t{\n2212:\t\tconst struct proto *prot = READ_ONCE(osk-\u003esk_prot);\n2213:\t#ifdef CONFIG_SECURITY_NETWORK\n2214:\t\tvoid *sptr = nsk-\u003esk_security;\n2215:\t#endif\n2216:\t\n2217:\t\t/* If we move sk_tx_queue_mapping out of the private section,\n2218:\t\t * we must check if sk_tx_queue_clear() is called after\n2219:\t\t * sock_copy() in sk_clone_lock().\n2220:\t\t */\n2221:\t\tBUILD_BUG_ON(offsetof(struct sock, sk_tx_queue_mapping) \u003c\n2222:\t\t\t     offsetof(struct sock, sk_dontcopy_begin) ||\n2223:\t\t\t     offsetof(struct sock, sk_tx_queue_mapping) \u003e=\n2224:\t\t\t     offsetof(struct sock, sk_dontcopy_end));\n2225:\t\n2226:\t\tmemcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));\n2227:\t\n2228:\t\tunsafe_memcpy(\u0026nsk-\u003esk_dontcopy_end, \u0026osk-\u003esk_dontcopy_end,\n2229:\t\t\t      prot-\u003eobj_size - offsetof(struct sock, sk_dontcopy_end),\n2230:\t\t\t      /* alloc is larger than struct, see sk_prot_alloc() */);\n2231:\t\n2232:\t#ifdef CONFIG_SECURITY_NETWORK\n2233:\t\tnsk-\u003esk_security = sptr;\n2234:\t\tsecurity_sk_clone(osk, nsk);\n2235:\t#endif\n2236:\t}\n2237:\t\n2238:\tstatic struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,\n2239:\t\t\tint family)\n2240:\t{\n2241:\t\tstruct sock *sk;\n2242:\t\tstruct kmem_cache *slab;\n2243:\t\n2244:\t\tslab = prot-\u003eslab;\n2245:\t\tif (slab != NULL) {\n2246:\t\t\tsk = kmem_cache_alloc(slab, priority \u0026 ~__GFP_ZERO);\n2247:\t\t\tif (!sk)\n2248:\t\t\t\treturn sk;\n2249:\t\t\tif (want_init_on_alloc(priority))\n"
}
51/3 2026/10/22 02:17 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 17957
							output: 36
							thoughts: 131

Thoughts: 
Here's my take on the thought process:

**Diving into Socket Cloning and Copying**

Okay, so `sock_copy` seems to handle copying data, but specifically *outside* the `dontcopy_begin` and `dontcopy_end` ranges, all the way up to `prot->obj_size`. That makes sense in the overall scheme. Now, I'm tracing through `sk_clone_lock`, and it calls `sk_clone`. `sk_clone` in turn uses `sk_prot_alloc` for memory allocation, which is what I'd expect. Now I'm on to `sk_clone`, looking at the function signature, seeing the important parameters.

```c
struct sock *sk_clone(const struct sock *sk, const gfp_t priority,
                      int family)
{
    struct sock *newsk;
    ...
}
```

Okay, the structure of it is clear enough. Time to get down into the details, specifically lines 2480-2520 of `net/core/sock.c`, let's see what's really happening.

52/3 2026/10/22 02:17 tool read-file
0m Args: 
{
  "File": "net/core/sock.c",
  "FirstLine": 2480,
  "LineCount": 40
}

Results: 
{
  "Contents": "2480:\tstruct sock *sk_clone(const struct sock *sk, const gfp_t priority,\n2481:\t\t\t      bool lock)\n2482:\t{\n2483:\t\tstruct proto *prot = READ_ONCE(sk-\u003esk_prot);\n2484:\t\tstruct sk_filter *filter;\n2485:\t\tbool is_charged = true;\n2486:\t\tstruct sock *newsk;\n2487:\t\n2488:\t\tnewsk = sk_prot_alloc(prot, priority, sk-\u003esk_family);\n2489:\t\tif (!newsk)\n2490:\t\t\tgoto out;\n2491:\t\n2492:\t\tsock_copy(newsk, sk);\n2493:\t\n2494:\t\tnewsk-\u003esk_prot_creator = prot;\n2495:\t#ifdef CONFIG_BPF_SYSCALL\n2496:\t\tRCU_INIT_POINTER(newsk-\u003esk_bpf_storage, NULL);\n2497:\t#endif\n2498:\t#if IS_ENABLED(CONFIG_INET_PSP)\n2499:\t\tDEBUG_NET_WARN_ON_ONCE(rcu_access_pointer(sk-\u003epsp_assoc));\n2500:\t#endif\n2501:\t\n2502:\t\t/* SANITY */\n2503:\t\tif (likely(newsk-\u003esk_net_refcnt)) {\n2504:\t\t\tget_net_track(sock_net(newsk), \u0026newsk-\u003ens_tracker, priority);\n2505:\t\t\tsock_inuse_add(sock_net(newsk), 1);\n2506:\t\t} else {\n2507:\t\t\t/* Kernel sockets are not elevating the struct net refcount.\n2508:\t\t\t * Instead, use a tracker to more easily detect if a layer\n2509:\t\t\t * is not properly dismantling its kernel sockets at netns\n2510:\t\t\t * destroy time.\n2511:\t\t\t */\n2512:\t\t\tnet_passive_inc(sock_net(newsk));\n2513:\t\t\t__netns_tracker_alloc(sock_net(newsk), \u0026newsk-\u003ens_tracker,\n2514:\t\t\t\t\t      false, priority);\n2515:\t\t}\n2516:\t\n2517:\t\tsk_node_init(\u0026newsk-\u003esk_node);\n2518:\t\tsock_lock_init(newsk);\n2519:\t\n"
}
53/3 2026/10/22 02:17 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 19008
							output: 34
							thoughts: 1109

Thoughts: 
**Analyzing the TCP Window Clamp Patch**

Okay, let's break this down. My initial thought is that `sock_copy` will copy everything, and `sk_alloc` zeroes everything, so new sockets are zeroed and cloned sockets are copied. That's good to keep in mind for the state of these variables.

Now, let's get into the nitty-gritty of this patch.

First, I see the documentation is updated to include `window_clamp_user`. Fine, a doc update is generally a good thing to see alongside a change.

Next, a new field, `u32 window_clamp_user`, is added to `tcp.h`. It's clearly meant to store a TCP_WINDOW_CLAMP value set by the user. Makes sense.

Then, there's this `tcp_req_window_clamp` inline function. The key is that it will return `window_clamp` if `window_clamp_user` has been set, otherwise, it defaults to the route window metric (`dst_metric`). The rationale is that for SYN-ACK and SYN cookie paths, the child's window scale needs to match the parent's. That's a classic TCP design consideration.

The `syncookies.c` changes are interesting. It's replacing a direct read of `tp->window_clamp` with a call to `tcp_req_window_clamp`. This is crucial because it's ensuring that the window clamp on the request socket now respects the user-configured value (if set) rather than blindly taking the route metric. This is where the patch actually changes the logic.

`tcp_set_rcvbuf` in `tcp.c` is also updated. It ensures that `window_clamp` follows the receive buffer, but never exceeds the user-set clamp. This seems like a reasonable constraint, to ensure the clamp is not accidentally exceeded by the buffer calculation.

In `tcp_disconnect`, `window_clamp` and `window_clamp_user` are explicitly reset to 0. This makes sense for cleanup. The important note is that `window_clamp_user` is reset via `WRITE_ONCE`.

`do_tcp_setsockopt` handles `TCP_WINDOW_CLAMP`. If a value is given, `tcp_set_window_clamp` is called, and `window_clamp_user` is set to either the current clamp or zero, depending on the value passed to the option. Nice, clean handling of the user setting.

`tcp_minisocks.c` updates how a request socket's initial window clamp is initialized by calling `tcp_req_window_clamp`, which ensures the behavior consistency described earlier.

In `tcp_output.c`, when initializing a connection, it looks like `window_clamp` is set to the route window metric *only if* `window_clamp_user` is zero. Otherwise, it is not modified (i.e. it keeps the user clamp). This makes sense, the initial value is route metric if not set by the user.

Finally, similar changes are applied to IPv6 syncookies, which further solidifies the need for the change.

I'd want to check `tcp_getsockopt` to confirm *what* exactly is returned there. Is it `window_clamp` or `window_clamp_user`? This patch makes the user-set clamp a first-class citizen; the get option should reflect that. I suspect we are returning `window_clamp` but it is important to check.

54/3 2026/10/22 02:17 tool grepper
0m Args: 
{
  "Expression": "TCP_WINDOW_CLAMP",
  "PathPrefixes": [
    "net/ipv4/tcp.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp.c=1860=void tcp_set_rcvbuf(struct sock *sk, int val)\n--\nnet/ipv4/tcp.c-1865-\t/* window_clamp follows the receive buffer, but never goes above a\nnet/ipv4/tcp.c:1866:\t * clamp the user set with TCP_WINDOW_CLAMP.\nnet/ipv4/tcp.c-1867-\t */\n--\nnet/ipv4/tcp.c=3850=int do_tcp_setsockopt(struct sock *sk, int level, int optname,\n--\nnet/ipv4/tcp.c-4067-\nnet/ipv4/tcp.c:4068:\tcase TCP_WINDOW_CLAMP:\nnet/ipv4/tcp.c-4069-\t\terr = tcp_set_window_clamp(sk, val);\n--\nnet/ipv4/tcp.c=4497=int do_tcp_getsockopt(struct sock *sk, int level,\n--\nnet/ipv4/tcp.c-4552-\t\tbreak;\nnet/ipv4/tcp.c:4553:\tcase TCP_WINDOW_CLAMP:\nnet/ipv4/tcp.c-4554-\t\tval = READ_ONCE(tp-\u003ewindow_clamp);\n"
}
55/3 2026/10/22 02:17 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 21241
							output: 26
							thoughts: 106

Thoughts: 
**Investigating a TCP Window Clamp Concern**

Okay, let's take a look at `do_tcp_getsockopt`. Specifically, I want to confirm my understanding of the `TCP_WINDOW_CLAMP` path. I see the code reads the `tp->window_clamp` value directly into `val`, which is an `int`, and then that `int` is copied out. Seems straightforward. Nothing jumps out as a potential issue there.

But wait a minute… just because it *looks* okay here doesn't mean there isn't something else going on. I need to be absolutely sure. Let me do a quick grep across the entire codebase. I'll search for every instance of `window_clamp`. That should reveal all interactions with `window_clamp` or related terms, both reads and writes. I want to see if any other function is touching it in an unexpected way, or setting it incorrectly. Let's see what turns up. This is where the real interesting information is likely to be.

56/3 2026/10/22 02:17 tool grepper
0m Args: 
{
  "Expression": "window_clamp",
  "PathPrefixes": [
    "net/"
  ]
}

Results: 
{
  "Output": "\nFull output is too long, showing 200 out of 252 lines.\nUse more precise expression or PathPrefixes if possible.\n\nNumber of matching lines per file (7 files in total):\nnet/ipv4/syncookies.c:4\nnet/ipv4/tcp.c:23\nnet/ipv4/tcp_input.c:20\nnet/ipv4/tcp_minisocks.c:6\nnet/ipv4/tcp_output.c:14\nnet/ipv6/syncookies.c:4\nnet/mptcp/sockopt.c:1\n\nnet/ipv4/syncookies.c=405=struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv4/syncookies.c-474-\t/* Try to redo what tcp_v4_send_synack did. */\nnet/ipv4/syncookies.c:475:\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, \u0026rt-\u003edst);\nnet/ipv4/syncookies.c-476-\t/* limit the window selection if the user enforce a smaller rx buffer */\n--\nnet/ipv4/syncookies.c-478-\tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\nnet/ipv4/syncookies.c:479:\t    (req-\u003ersk_window_clamp \u003e full_space || req-\u003ersk_window_clamp == 0))\nnet/ipv4/syncookies.c:480:\t\treq-\u003ersk_window_clamp = full_space;\nnet/ipv4/syncookies.c-481-\nnet/ipv4/syncookies.c-482-\ttcp_select_initial_window(sk, full_space, req-\u003emss,\nnet/ipv4/syncookies.c:483:\t\t\t\t  \u0026req-\u003ersk_rcv_wnd, \u0026req-\u003ersk_window_clamp,\nnet/ipv4/syncookies.c-484-\t\t\t\t  ireq-\u003ewscale_ok, \u0026rcv_wscale,\n--\nnet/ipv4/tcp.c=1554=void __tcp_cleanup_rbuf(struct sock *sk, int copied)\n--\nnet/ipv4/tcp.c-1587-\t\t/* Optimize, __tcp_select_window() is not cheap. */\nnet/ipv4/tcp.c:1588:\t\tif (2*rcv_window_now \u003c= tp-\u003ewindow_clamp) {\nnet/ipv4/tcp.c-1589-\t\t\t__u32 new_window = __tcp_select_window(sk);\n--\nnet/ipv4/tcp.c=1832=int tcp_set_rcvlowat(struct sock *sk, int val)\n--\nnet/ipv4/tcp.c-1853-\nnet/ipv4/tcp.c:1854:\t\tif (tp-\u003ewindow_clamp \u0026\u0026 tp-\u003ewindow_clamp \u003c val)\nnet/ipv4/tcp.c:1855:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, val);\nnet/ipv4/tcp.c-1856-\t}\n--\nnet/ipv4/tcp.c=1860=void tcp_set_rcvbuf(struct sock *sk, int val)\nnet/ipv4/tcp.c-1861-{\nnet/ipv4/tcp.c:1862:\tu32 user_clamp = tcp_sk(sk)-\u003ewindow_clamp_user;\nnet/ipv4/tcp.c-1863-\tint win = tcp_win_from_space(sk, val);\nnet/ipv4/tcp.c-1864-\nnet/ipv4/tcp.c:1865:\t/* window_clamp follows the receive buffer, but never goes above a\nnet/ipv4/tcp.c-1866-\t * clamp the user set with TCP_WINDOW_CLAMP.\n--\nnet/ipv4/tcp.c-1869-\t\twin = min_t(u32, win, user_clamp);\nnet/ipv4/tcp.c:1870:\ttcp_set_window_clamp(sk, win);\nnet/ipv4/tcp.c-1871-}\n--\nnet/ipv4/tcp.c=3373=int tcp_disconnect(struct sock *sk, int flags)\n--\nnet/ipv4/tcp.c-3438-\ttp-\u003emax_packets_out = 0;\nnet/ipv4/tcp.c:3439:\ttp-\u003ewindow_clamp = 0;\nnet/ipv4/tcp.c:3440:\tWRITE_ONCE(tp-\u003ewindow_clamp_user, 0);\nnet/ipv4/tcp.c-3441-\ttp-\u003edelivered = 0;\n--\nnet/ipv4/tcp.c=3800=EXPORT_SYMBOL(tcp_sock_set_keepcnt);\nnet/ipv4/tcp.c-3801-\nnet/ipv4/tcp.c:3802:int tcp_set_window_clamp(struct sock *sk, int val)\nnet/ipv4/tcp.c-3803-{\nnet/ipv4/tcp.c:3804:\tu32 old_window_clamp, new_window_clamp, new_rcv_ssthresh;\nnet/ipv4/tcp.c-3805-\tstruct tcp_sock *tp = tcp_sk(sk);\n--\nnet/ipv4/tcp.c-3809-\t\t\treturn -EINVAL;\nnet/ipv4/tcp.c:3810:\t\tWRITE_ONCE(tp-\u003ewindow_clamp, 0);\nnet/ipv4/tcp.c-3811-\t\treturn 0;\n--\nnet/ipv4/tcp.c-3813-\nnet/ipv4/tcp.c:3814:\told_window_clamp = tp-\u003ewindow_clamp;\nnet/ipv4/tcp.c:3815:\tnew_window_clamp = max_t(int, SOCK_MIN_RCVBUF / 2, val);\nnet/ipv4/tcp.c-3816-\nnet/ipv4/tcp.c:3817:\tif (new_window_clamp == old_window_clamp)\nnet/ipv4/tcp.c-3818-\t\treturn 0;\nnet/ipv4/tcp.c-3819-\nnet/ipv4/tcp.c:3820:\tWRITE_ONCE(tp-\u003ewindow_clamp, new_window_clamp);\nnet/ipv4/tcp.c-3821-\n--\nnet/ipv4/tcp.c-3824-\t */\nnet/ipv4/tcp.c:3825:\tif (new_window_clamp \u003c old_window_clamp) {\nnet/ipv4/tcp.c:3826:\t\t__tcp_adjust_rcv_ssthresh(sk, new_window_clamp);\nnet/ipv4/tcp.c-3827-\t} else {\nnet/ipv4/tcp.c:3828:\t\tnew_rcv_ssthresh = min(tp-\u003ercv_wnd, new_window_clamp);\nnet/ipv4/tcp.c-3829-\t\ttp-\u003ercv_ssthresh = max(new_rcv_ssthresh, tp-\u003ercv_ssthresh);\n--\nnet/ipv4/tcp.c=3850=int do_tcp_setsockopt(struct sock *sk, int level, int optname,\n--\nnet/ipv4/tcp.c-4068-\tcase TCP_WINDOW_CLAMP:\nnet/ipv4/tcp.c:4069:\t\terr = tcp_set_window_clamp(sk, val);\nnet/ipv4/tcp.c-4070-\t\tif (!err)\nnet/ipv4/tcp.c:4071:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp_user,\nnet/ipv4/tcp.c:4072:\t\t\t\t   val ? tp-\u003ewindow_clamp : 0);\nnet/ipv4/tcp.c-4073-\t\tbreak;\n--\nnet/ipv4/tcp.c=4497=int do_tcp_getsockopt(struct sock *sk, int level,\n--\nnet/ipv4/tcp.c-4553-\tcase TCP_WINDOW_CLAMP:\nnet/ipv4/tcp.c:4554:\t\tval = READ_ONCE(tp-\u003ewindow_clamp);\nnet/ipv4/tcp.c-4555-\t\tbreak;\n--\nnet/ipv4/tcp.c=5214=static void __init tcp_struct_check(void)\n--\nnet/ipv4/tcp.c-5283-\tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, snd_una);\nnet/ipv4/tcp.c:5284:\tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, window_clamp);\nnet/ipv4/tcp.c-5285-\tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, srtt_us);\n--\nnet/ipv4/tcp_input.c=227=static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)\n--\nnet/ipv4/tcp_input.c-254-\t\t\t\tval = tcp_win_from_space(sk, sk-\u003esk_rcvbuf);\nnet/ipv4/tcp_input.c:255:\t\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp, val);\nnet/ipv4/tcp_input.c-256-\nnet/ipv4/tcp_input.c:257:\t\t\t\tif (tp-\u003ewindow_clamp \u003c tp-\u003ercvq_space.space)\nnet/ipv4/tcp_input.c:258:\t\t\t\t\ttp-\u003ercvq_space.space = tp-\u003ewindow_clamp;\nnet/ipv4/tcp_input.c-259-\t\t\t}\n--\nnet/ipv4/tcp_input.c=605=static void tcp_sndbuf_expand(struct sock *sk)\n--\nnet/ipv4/tcp_input.c-636-\nnet/ipv4/tcp_input.c:637:/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)\nnet/ipv4/tcp_input.c-638- *\n--\nnet/ipv4/tcp_input.c-642- * latencies from network.\nnet/ipv4/tcp_input.c:643: * window_clamp is maximal advertised window. It can be less than\nnet/ipv4/tcp_input.c:644: * tcp_full_space(), in this case tcp_full_space() - window_clamp\nnet/ipv4/tcp_input.c:645: * is reserved for \"application\" buffer. The less window_clamp is\nnet/ipv4/tcp_input.c-646- * the smoother our behaviour from viewpoint of network, but the lower\n--\nnet/ipv4/tcp_input.c-648- *\nnet/ipv4/tcp_input.c:649: * rcv_ssthresh is more strict window_clamp used at \"slow start\"\nnet/ipv4/tcp_input.c-650- * phase to predict further behaviour of this connection.\n--\nnet/ipv4/tcp_input.c=700=static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,\n--\nnet/ipv4/tcp_input.c-705-\nnet/ipv4/tcp_input.c:706:\troom = min_t(int, tp-\u003ewindow_clamp, tcp_space(sk)) - tp-\u003ercv_ssthresh;\nnet/ipv4/tcp_input.c-707-\n--\nnet/ipv4/tcp_input.c=740=static void tcp_init_buffer_space(struct sock *sk)\n--\nnet/ipv4/tcp_input.c-754-\nnet/ipv4/tcp_input.c:755:\tif (tp-\u003ewindow_clamp \u003e= maxwin) {\nnet/ipv4/tcp_input.c:756:\t\tWRITE_ONCE(tp-\u003ewindow_clamp, maxwin);\nnet/ipv4/tcp_input.c-757-\nnet/ipv4/tcp_input.c-758-\t\tif (tcp_app_win \u0026\u0026 maxwin \u003e 4 * tp-\u003eadvmss)\nnet/ipv4/tcp_input.c:759:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp,\nnet/ipv4/tcp_input.c-760-\t\t\t\t   max(maxwin - (maxwin \u003e\u003e tcp_app_win),\n--\nnet/ipv4/tcp_input.c-765-\tif (tcp_app_win \u0026\u0026\nnet/ipv4/tcp_input.c:766:\t    tp-\u003ewindow_clamp \u003e 2 * tp-\u003eadvmss \u0026\u0026\nnet/ipv4/tcp_input.c:767:\t    tp-\u003ewindow_clamp + tp-\u003eadvmss \u003e maxwin)\nnet/ipv4/tcp_input.c:768:\t\tWRITE_ONCE(tp-\u003ewindow_clamp,\nnet/ipv4/tcp_input.c-769-\t\t\t   max(2 * tp-\u003eadvmss, maxwin - tp-\u003eadvmss));\nnet/ipv4/tcp_input.c-770-\nnet/ipv4/tcp_input.c:771:\ttp-\u003ercv_ssthresh = min(tp-\u003ercv_ssthresh, tp-\u003ewindow_clamp);\nnet/ipv4/tcp_input.c-772-\ttp-\u003esnd_cwnd_stamp = tcp_jiffies32;\n--\nnet/ipv4/tcp_input.c=778=static void tcp_clamp_window(struct sock *sk)\n--\nnet/ipv4/tcp_input.c-795-\tif (atomic_read(\u0026sk-\u003esk_rmem_alloc) \u003e sk-\u003esk_rcvbuf)\nnet/ipv4/tcp_input.c:796:\t\ttp-\u003ercv_ssthresh = min(tp-\u003ewindow_clamp, 2U * tp-\u003eadvmss);\nnet/ipv4/tcp_input.c-797-}\n--\nnet/ipv4/tcp_input.c=911=void tcp_rcvbuf_grow(struct sock *sk, u32 newval)\n--\nnet/ipv4/tcp_input.c-951-\t\t/* Make the window clamp follow along.  */\nnet/ipv4/tcp_input.c:952:\t\tWRITE_ONCE(tp-\u003ewindow_clamp,\nnet/ipv4/tcp_input.c-953-\t\t\t   tcp_win_from_space(sk, rcvbuf));\n--\nnet/ipv4/tcp_input.c=6872=static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,\n--\nnet/ipv4/tcp_input.c-6968-\t\t\ttp-\u003erx_opt.snd_wscale = tp-\u003erx_opt.rcv_wscale = 0;\nnet/ipv4/tcp_input.c:6969:\t\t\tWRITE_ONCE(tp-\u003ewindow_clamp,\nnet/ipv4/tcp_input.c:6970:\t\t\t\t   min(tp-\u003ewindow_clamp, 65535U));\nnet/ipv4/tcp_input.c-6971-\t\t}\n--\nnet/ipv4/tcp_minisocks.c=431=void tcp_openreq_init_rwin(struct request_sock *req,\n--\nnet/ipv4/tcp_minisocks.c-443-\t/* Set this up on the first call only */\nnet/ipv4/tcp_minisocks.c:444:\treq-\u003ersk_window_clamp = tcp_req_window_clamp(tp, dst);\nnet/ipv4/tcp_minisocks.c-445-\n--\nnet/ipv4/tcp_minisocks.c-447-\tif (sk_listener-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\nnet/ipv4/tcp_minisocks.c:448:\t    (req-\u003ersk_window_clamp \u003e full_space || req-\u003ersk_window_clamp == 0))\nnet/ipv4/tcp_minisocks.c:449:\t\treq-\u003ersk_window_clamp = full_space;\nnet/ipv4/tcp_minisocks.c-450-\n--\nnet/ipv4/tcp_minisocks.c-460-\t\t\u0026req-\u003ersk_rcv_wnd,\nnet/ipv4/tcp_minisocks.c:461:\t\t\u0026req-\u003ersk_window_clamp,\nnet/ipv4/tcp_minisocks.c-462-\t\tireq-\u003ewscale_ok,\n--\nnet/ipv4/tcp_minisocks.c=544=struct sock *tcp_create_openreq_child(const struct sock *sk,\n--\nnet/ipv4/tcp_minisocks.c-598-\tnewtp-\u003erx_opt.sack_ok = ireq-\u003esack_ok;\nnet/ipv4/tcp_minisocks.c:599:\tnewtp-\u003ewindow_clamp = req-\u003ersk_window_clamp;\nnet/ipv4/tcp_minisocks.c-600-\tnewtp-\u003ercv_ssthresh = req-\u003ersk_rcv_wnd;\n--\nnet/ipv4/tcp_minisocks.c-608-\t\tnewtp-\u003erx_opt.snd_wscale = newtp-\u003erx_opt.rcv_wscale = 0;\nnet/ipv4/tcp_minisocks.c:609:\t\tnewtp-\u003ewindow_clamp = min(newtp-\u003ewindow_clamp, 65535U);\nnet/ipv4/tcp_minisocks.c-610-\t}\n--\nnet/ipv4/tcp_output.c=223=void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,\nnet/ipv4/tcp_output.c:224:\t\t\t       __u32 *rcv_wnd, __u32 *__window_clamp,\nnet/ipv4/tcp_output.c-225-\t\t\t       int wscale_ok, __u8 *rcv_wscale,\n--\nnet/ipv4/tcp_output.c-228-\tunsigned int space = (__space \u003c 0 ? 0 : __space);\nnet/ipv4/tcp_output.c:229:\tu32 window_clamp = READ_ONCE(*__window_clamp);\nnet/ipv4/tcp_output.c-230-\nnet/ipv4/tcp_output.c-231-\t/* If no clamp set the clamp to the max possible scaled window */\nnet/ipv4/tcp_output.c:232:\tif (window_clamp == 0)\nnet/ipv4/tcp_output.c:233:\t\twindow_clamp = (U16_MAX \u003c\u003c TCP_MAX_WSCALE);\nnet/ipv4/tcp_output.c:234:\tspace = min(window_clamp, space);\n\n"
}
57/3 2026/10/22 02:17 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 26394
							output: 34
							thoughts: 407

Thoughts: 
**Analyzing the TCP Window Clamp Patch**

Okay, let's break down this patch and its implications. My primary concern here is the impact on existing behavior and, crucially, the potential for introducing uninitialized memory vulnerabilities.

The core issue seems to be how `SO_RCVBUF` interacts with the `window_clamp` field on unconnected or listening sockets. Essentially, a previous commit, `b025461303d8`, changed the expected behavior, leading to `tp->window_clamp` no longer being zero after `SO_RCVBUF` is set. This means code that previously relied on a zero value to determine if the window clamp was explicitly set, and potentially used route metrics (like `RTAX_WINDOW`) if not, is now being misled.

The proposed solution looks sound. The patch introduces a `window_clamp_user` variable. This separates whether the clamp was set explicitly via `setsockopt(TCP_WINDOW_CLAMP)` from the `window_clamp` field itself. Initialization, specifically zero-initialization using `__GFP_ZERO` during socket allocation (`sk_alloc()`), is crucial here. I'm also glad to see the reset of `tp->window_clamp_user` to zero during socket disconnection (`tcp_disconnect()`). This is critical to ensure proper behavior after the socket is no longer actively connected. The update logic when `setsockopt(TCP_WINDOW_CLAMP)` is called also looks correct; it now sets `tp->window_clamp_user` based on the value passed to the option.

Now, the important question – uninitialized memory. Let's make sure nothing is being exposed to user space that could leak sensitive data, or worse, allow arbitrary code execution. We need to check if `window_clamp_user` is part of any structures sent to user space via system calls like `getsockopt(TCP_INFO)`, netlink, or anything else that exposes socket information. Let's specifically look at `tcp_get_info` in `net/ipv4/tcp.c`. We're going to make sure that no new fields are being exposed or that existing structures haven't been modified in a way that creates a gap that the user could potentially read.

58/3 2026/10/22 02:17 tool grepper
0m Args: 
{
  "Expression": "tcp_get_info",
  "PathPrefixes": [
    "net/ipv4/tcp.c"
  ]
}

Results: 
{
  "Output": "net/ipv4/tcp.c=4188=int tcp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,\n--\nnet/ipv4/tcp.c-4199-\nnet/ipv4/tcp.c:4200:static void tcp_get_info_chrono_stats(const struct tcp_sock *tp,\nnet/ipv4/tcp.c-4201-\t\t\t\t      struct tcp_info *info)\n--\nnet/ipv4/tcp.c-4225-/* Return information about state of tcp endpoint in API format. */\nnet/ipv4/tcp.c:4226:void tcp_get_info(struct sock *sk, struct tcp_info *info)\nnet/ipv4/tcp.c-4227-{\n--\nnet/ipv4/tcp.c-4325-\tinfo-\u003etcpi_notsent_bytes = max_t(int, 0, tp-\u003ewrite_seq - tp-\u003esnd_nxt);\nnet/ipv4/tcp.c:4326:\ttcp_get_info_chrono_stats(tp, info);\nnet/ipv4/tcp.c-4327-\n--\nnet/ipv4/tcp.c-4378-}\nnet/ipv4/tcp.c:4379:EXPORT_SYMBOL_GPL(tcp_get_info);\nnet/ipv4/tcp.c-4380-\n--\nnet/ipv4/tcp.c=4425=struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,\n--\nnet/ipv4/tcp.c-4438-\nnet/ipv4/tcp.c:4439:\ttcp_get_info_chrono_stats(tp, \u0026info);\nnet/ipv4/tcp.c-4440-\tnla_put_u64_64bit(stats, TCP_NLA_BUSY,\n--\nnet/ipv4/tcp.c=4497=int do_tcp_getsockopt(struct sock *sk, int level,\n--\nnet/ipv4/tcp.c-4561-\nnet/ipv4/tcp.c:4562:\t\ttcp_get_info(sk, \u0026info);\nnet/ipv4/tcp.c-4563-\n"
}
59/3 2026/10/22 02:17 llm kmsan-evaluator
0m Model: 
gemini-3.8-flash

Args: 
null

Results: 
null

Tokens: 
							input: 27891
							output: 355
							thoughts: 1069

Thoughts: 
**KMSAN Assessment of TCP Window Clamp User Implementation**

Okay, let's break this down. My initial thought is to verify whether `window_clamp_user` is part of `tcp_info`, but I remember that `tcp_info` is a UAPI struct, so that's a dead end. This new field resides within the internal kernel structure, `struct tcp_sock`.

Next, I need to make sure there are no uninitialized variables being used in conditional logic.  From what I see, `tp->window_clamp_user` is *always* initialized. Socket allocation uses `__GFP_ZERO` via `sk_alloc()`. Cloning uses `sock_copy()` which does a `memcpy` of the struct.  It's zeroed in `tcp_disconnect`, and set in `do_tcp_setsockopt` with a clear conditional ensuring initialization with `TCP_WINDOW_CLAMP`. Reads are handled with `READ_ONCE`, meaning that memory visibility is correct.

Now, let's scrutinize `tcp_req_window_clamp`. This function seems straightforward: If `READ_ONCE(tp->window_clamp_user)` is true, return the user-set `window_clamp`. Otherwise, return a metric from the destination.  There’s no uninitialized memory access here. This is a simple conditional read.  The patch is changing the condition from `window_clamp` to `window_clamp_user`, which is the correct change to make.

There's no opportunity here for buffer overflows, out-of-bounds reads, or anything like that. No buffers or packet payloads are being read or accessed. This is all about window scaling and advertised window calculation.

Regarding information leaks, there are none.

As for other detectors, KCSAN will deal with concurrency issues; logic bugs would be functional, caught by the added unit/packetdrill tests. KASAN would handle memory bounds and lifetime problems, which aren't relevant here. KMSAN would catch uninitialized memory reads or leaks to userspace.

Okay, let’s go through a thorough KMSAN check. No new padding is exposed to userspace. No `copy_to_user` or `put_user` calls involving uninitialized fields. `struct tcp_sock` is `__GFP_ZERO` allocated. `window_clamp_user` is just a u32 inside a field or cacheline hole. No stack buffers, heap allocations with uninitialized data, or bitfields are present. There is no change to data length calculations that could cause KMSAN to detect a problem.

Therefore, `NeedsKMSAN` is `false`.

To be crystal clear, here's my justification: This patch introduces `window_clamp_user` to differentiate between user-set and internally adjusted window clamping. `struct tcp_sock` is zeroed during allocation and clone. `window_clamp_user` is *always* explicitly initialized. No uninitialized fields are exposed to userspace. The changes deal with TCP window sizing only, affecting integer arithmetic and window control. Therefore, KASAN and the other detectors are sufficient, and KMSAN is not needed here.

60/3 2026/10/22 02:17 tool set-results
0m Args: 
{
  "KMSANReasoning": "The patch series resolves an issue where setting SO_RCVBUF unintentionally overwrote `tp-\u003ewindow_clamp`, causing TCP window calculations on connect, listen, or SYN cookies to mistake receive buffer adjustments for user-configured window clamps. To fix this, it adds `tp-\u003ewindow_clamp_user` to `struct tcp_sock` to track whether `TCP_WINDOW_CLAMP` was explicitly set by the user.\n\nKMSAN applicability assessment:\n1. Memory initialization: Sockets (`struct tcp_sock`) are allocated with `__GFP_ZERO` via `sk_alloc()` and cloned via `sock_copy()` in `sk_clone()`. The new field `window_clamp_user` is initialized to zero upon allocation, cleared on `tcp_disconnect()`, and set explicitly in `do_tcp_setsockopt()`. It is never read uninitialized.\n2. Kernel-to-user info leaks: The patch does not expose any new fields or structures to user space; `window_clamp_user` is an internal TCP state variable not copied to user space.\n3. Buffer parsing and length handling: The change modifies TCP window clamp calculations and route metric lookups (`tcp_req_window_clamp()`). No packet buffer slicing, payload accesses, or memory copying operations are altered in ways that could expose uninitialized buffer memory.\n\nBecause no uninitialized memory reads or information leak risks are introduced or exposed, dedicated KMSAN fuzzing is not required. Any functional or concurrency issues are sufficiently covered by packetdrill tests, KASAN, and KCSAN.",
  "NeedsKMSAN": false
}

Results: 
{
  "KMSANReasoning": "The patch series resolves an issue where setting SO_RCVBUF unintentionally overwrote `tp-\u003ewindow_clamp`, causing TCP window calculations on connect, listen, or SYN cookies to mistake receive buffer adjustments for user-configured window clamps. To fix this, it adds `tp-\u003ewindow_clamp_user` to `struct tcp_sock` to track whether `TCP_WINDOW_CLAMP` was explicitly set by the user.\n\nKMSAN applicability assessment:\n1. Memory initialization: Sockets (`struct tcp_sock`) are allocated with `__GFP_ZERO` via `sk_alloc()` and cloned via `sock_copy()` in `sk_clone()`. The new field `window_clamp_user` is initialized to zero upon allocation, cleared on `tcp_disconnect()`, and set explicitly in `do_tcp_setsockopt()`. It is never read uninitialized.\n2. Kernel-to-user info leaks: The patch does not expose any new fields or structures to user space; `window_clamp_user` is an internal TCP state variable not copied to user space.\n3. Buffer parsing and length handling: The change modifies TCP window clamp calculations and route metric lookups (`tcp_req_window_clamp()`). No packet buffer slicing, payload accesses, or memory copying operations are altered in ways that could expose uninitialized buffer memory.\n\nBecause no uninitialized memory reads or information leak risks are introduced or exposed, dedicated KMSAN fuzzing is not required. Any functional or concurrency issues are sufficiently covered by packetdrill tests, KASAN, and KCSAN.",
  "NeedsKMSAN": false
}
LLM Calls Summary:
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Tool Calls Summary:
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