AI Trajectory

Trajectory: (Expand/Collapse All)
Seq	Timestamp	Type	Name	Duration
0/0	2026/09/17 15:00	flow	patch-triage	17m Args: null Results: { "EnableConfigs": [ "INET", "IPV6", "SYN_COOKIES", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "sol_tcp_sockopt", "tcp_ecn_create_request", "tcp_syn_options", "tcp_synack_options", "tcp_established_options", "cookie_v4_check", "cookie_v6_check" ], "KMSANReasoning": "The patch introduces per-socket configuration for TCP ECN mode (TCP_ECN) and Accurate ECN option sending behavior (TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, adding two u8 fields (ecn_mode and ecn_option) to struct tcp_sock.\n\nAnalysis of uninitialized memory risk:\n1. Field initialization: The new fields `tp-\u003eecn_mode` and `tp-\u003eecn_option` are explicitly initialized in `tcp_init_sock()` to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. Child sockets cloned during incoming connections via `tcp_create_openreq_child()` inherit these fields from the listening socket via `inet_csk_clone_lock()`.\n2. Getsockopt / copy to userspace: In `do_tcp_getsockopt()`, reading `TCP_ECN` or `TCP_ECN_OPTION` reads the u8 value into a local scalar `int val`, which is fully initialized (zero-extended) before `copy_to_sockptr()`. No uninitialized memory or structure padding is exposed or leaked to userspace or BPF.\n3. Setsockopt / input handling: `do_tcp_setsockopt()` validates integer input bounds and writes valid values to the struct fields.\n4. Surrounding logic: The helper functions `tcp_ecn_mode_eff()` and `tcp_accecn_option_eff()` fallback cleanly to the netns sysctl values if the per-socket option is unspecified. No conditional branches operate on uninitialized variables or memory buffers.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not justified. Standard KASAN fuzzing and compiler warnings/UBSAN are sufficient.", "NeedsKMSAN": false, "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options (and BPF sockopt support) allowing per-socket overrides for ECN and AccECN behavior. It alters TCP socket option handling, option formatting in SYN/SYN-ACK/established packets, SYN cookie processing, and connection request creation in reachable core networking code.", "WorthFuzzing": true }
1/1	2026/09/17 15:00	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit 5284afe60b184262a326325db48301b3fe54f95a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Thu Sep 17 14:59:59 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst\nindex 208f46967ee59..2e55d9e2eb09a 100644\n--- a/Documentation/networking/ip-sysctl.rst\n+++ b/Documentation/networking/ip-sysctl.rst\n@@ -528,6 +528,43 @@ tcp_ecn_fallback - BOOLEAN\n \n \tDefault: 1 (enabled)\n \n+tcp_ecn (socket option) - TCP_ECN\n+\tPer-socket control of ECN mode, allowing per-connection override of the\n+\ttcp_ecn sysctl setting. This enables L4S (Low Latency, Low Loss, Scalable\n+\tThroughput) configuration on a per-socket basis.\n+\n+\tSetting this socket option to any value except 255 will override the\n+\tsystem-wide tcp_ecn sysctl for that particular socket. A value of 255\n+\t(TCP_ECN_MODE_UNSPEC) means use the system default sysctl value.\n+\n+\tPossible values: 0-5 (see tcp_ecn sysctl description above), or 255 to\n+\tuse the system default (sysctl_tcp_ecn).\n+\n+\tExample::\n+\n+\t\tint val = 3; /* AccECN mode /\n+\t\tsetsockopt(fd, SOL_TCP, TCP_ECN, \u0026val, sizeof(val));\n+\n+\tDefault: 255 (unspecified - uses tcp_ecn sysctl value)\n+\n+tcp_ecn_option (socket option) - TCP_ECN_OPTION\n+\tPer-socket control of Accurate ECN (AccECN) option sending behavior,\n+\tallowing per-connection override of the tcp_ecn_option sysctl setting.\n+\n+\tSetting this socket option to any value except 255 will override the\n+\tsystem-wide tcp_ecn_option sysctl for that particular socket. A value of\n+\t255 (TCP_ACCECN_OPTION_UNSPEC) means use the system default sysctl value.\n+\n+\tPossible values: 0-3 (see tcp_ecn_option sysctl description above), or 255\n+\tto use the system default (sysctl_tcp_ecn_option).\n+\n+\tExample::\n+\n+\t\tint val = 2; / Send AccECN option on every packet /\n+\t\tsetsockopt(fd, SOL_TCP, TCP_ECN_OPTION, \u0026val, sizeof(val));\n+\n+\tDefault: 255 (unspecified - uses tcp_ecn_option sysctl value)\n+\n tcp_fack - BOOLEAN\n \tThis is a legacy option, it has no effect anymore.\n \ndiff --git a/include/linux/tcp.h b/include/linux/tcp.h\nindex 6a8c77719322f..7cb1e765f4618 100644\n--- a/include/linux/tcp.h\n+++ b/include/linux/tcp.h\n@@ -289,6 +289,13 @@ struct tcp_sock {\n \t\t\t\t\t sacked_out \u003e 0)\n \t\t\t\t\t /\n \tu8\tecn_flags;\t/ ECN status bits.\t\t\t/\n+\tu8\tecn_mode;\t/ Per-socket ECN mode override\n+\t\t\t\t * (TCP_ECN_MODE_UNSPEC = use sysctl)\n+\t\t\t\t /\n+\tu8\tecn_option;\t/ Per-socket AccECN option override\n+\t\t\t\t * (TCP_ACCECN_OPTION_UNSPEC = use sysctl)\n+\t\t\t\t /\n+\n \t__cacheline_group_end(tcp_sock_write_tx);\n \n \t/ TXRX read-write hotpath cache lines /\ndiff --git a/include/net/tcp.h b/include/net/tcp.h\nindex 5e5f5f9b89a38..b7c0b519ac078 100644\n--- a/include/net/tcp.h\n+++ b/include/net/tcp.h\n@@ -707,12 +707,6 @@ u64 cookie_init_timestamp(struct request_sock req, u64 now);\n bool cookie_timestamp_decode(const struct net net,\n \t\t\t struct tcp_options_received opt);\n \n-static inline bool cookie_ecn_ok(const struct net net, const struct dst_entry dst)\n-{\n-\treturn READ_ONCE(net-\u003eipv4.sysctl_tcp_ecn) \|\|\n-\t\tdst_feature(dst, RTAX_FEATURE_ECN);\n-}\n-\n #if IS_ENABLED(CONFIG_BPF)\n static inline bool cookie_bpf_ok(struct sk_buff skb)\n {\ndiff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h\nindex 865d5c5a7718d..48e364c458b29 100644\n--- a/include/net/tcp_ecn.h\n+++ b/include/net/tcp_ecn.h\n@@ -22,6 +22,7 @@ enum tcp_ecn_mode {\n \tTCP_ECN_IN_ACCECN_OUT_ACCECN = 3,\n \tTCP_ECN_IN_ACCECN_OUT_ECN = 4,\n \tTCP_ECN_IN_ACCECN_OUT_NOECN = 5,\n+\tTCP_ECN_MODE_UNSPEC = 255,\t/ Use sysctl default (per-socket) /\n };\n \n / AccECN option sending when AccECN has been successfully negotiated /\n@@ -30,8 +31,36 @@ enum tcp_accecn_option {\n \tTCP_ACCECN_OPTION_MINIMUM = 1,\n \tTCP_ACCECN_OPTION_FULL = 2,\n \tTCP_ACCECN_OPTION_PERSIST = 3,\n+\tTCP_ACCECN_OPTION_UNSPEC = 255,\t/ Use sysctl default (per-socket) /\n };\n \n+/ Resolve the effective ECN mode: per-socket override or sysctl fallback /\n+static inline u8 tcp_ecn_mode_eff(const struct sock sk)\n+{\n+\tu8 mode = READ_ONCE(tcp_sk(sk)-\u003eecn_mode);\n+\n+\tif (mode == TCP_ECN_MODE_UNSPEC)\n+\t\treturn READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn);\n+\treturn mode;\n+}\n+\n+/* Resolve the effective AccECN option: per-socket override or sysctl fallback /\n+static inline u8 tcp_accecn_option_eff(const struct sock sk)\n+{\n+\tu8 opt = READ_ONCE(tcp_sk(sk)-\u003eecn_option);\n+\n+\tif (opt == TCP_ACCECN_OPTION_UNSPEC)\n+\t\treturn READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn_option);\n+\treturn opt;\n+}\n+\n+/* ECN support for SYN cookies: per-socket override or route feature /\n+static inline bool cookie_ecn_ok(const struct sock sk, const struct dst_entry dst)\n+{\n+\treturn tcp_ecn_mode_eff(sk) \|\|\n+\t\tdst_feature(dst, RTAX_FEATURE_ECN);\n+}\n+\n / Apply either ECT(0) or ECT(1) based on TCP_CONG_ECT_1_NEGOTIATION flag /\n static inline void INET_ECN_xmit_ect_1_negotiation(struct sock sk)\n {\n@@ -599,7 +628,7 @@ static inline void tcp_ecn_send_syn(struct sock sk, struct sk_buff skb)\n \tstruct tcp_sock tp = tcp_sk(sk);\n \tbool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk);\n \tbool use_ecn, use_accecn;\n-\tu8 tcp_ecn = READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn);\n+\tu8 tcp_ecn = tcp_ecn_mode_eff(sk);\n \n \tuse_accecn = tcp_ecn == TCP_ECN_IN_ACCECN_OUT_ACCECN \|\|\n \t\t tcp_ca_needs_accecn(sk);\ndiff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h\nindex 732b35cc08d1c..c58b1633bb46e 100644\n--- a/include/uapi/linux/bpf.h\n+++ b/include/uapi/linux/bpf.h\n@@ -2985,7 +2985,8 @@ union bpf_attr {\n \t\t TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT,\n * \t\t TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP,\n * \t\t TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX,\n- \t\t TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS.\n+ \t\t TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS,\n+ \t\t TCP_ECN, TCP_ECN_OPTION.\n \t\t* IPPROTO_IP, which supports optname IP_TOS.\n * \t\t* IPPROTO_IPV6, which supports the following optname\\ s:\n * \t\t IPV6_TCLASS, IPV6_AUTOFLOWLABEL.\ndiff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h\nindex 03772dd4d3992..01ebb348ba274 100644\n--- a/include/uapi/linux/tcp.h\n+++ b/include/uapi/linux/tcp.h\n@@ -142,6 +142,8 @@ enum {\n #define TCP_RTO_MAX_MS\t\t44\t/* max rto time in ms /\n #define TCP_RTO_MIN_US\t\t45\t/ min rto time in us /\n #define TCP_DELACK_MAX_US\t46\t/ max delayed ack time in us /\n+#define TCP_ECN\t\t\t47\t/ Per-socket ECN mode (0-5, 255=use sysctl) /\n+#define TCP_ECN_OPTION\t\t48\t/ Per-socket AccECN option (0-3, 255=use sysctl) /\n \n #define TCP_REPAIR_ON\t\t1\n #define TCP_REPAIR_OFF\t\t0\ndiff --git a/net/core/filter.c b/net/core/filter.c\nindex 61940e7535523..993b31e10b944 100644\n--- a/net/core/filter.c\n+++ b/net/core/filter.c\n@@ -5670,6 +5670,8 @@ static int sol_tcp_sockopt(struct sock sk, int optname,\n \tcase TCP_NOTSENT_LOWAT:\n \tcase TCP_SAVE_SYN:\n \tcase TCP_RTO_MAX_MS:\n+\tcase TCP_ECN:\n+\tcase TCP_ECN_OPTION:\n \t\tif (optlen != sizeof(int))\n \t\t\treturn -EINVAL;\n \t\tbreak;\ndiff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c\nindex 73e1297681847..ebc438bc6a461 100644\n--- a/net/ipv4/syncookies.c\n+++ b/net/ipv4/syncookies.c\n@@ -490,7 +490,7 @@ struct sock cookie_v4_check(struct sock sk, struct sk_buff skb)\n \t /\n \tif (!req-\u003esyncookie)\n \t\tireq-\u003ercv_wscale = rcv_wscale;\n-\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(net, \u0026rt-\u003edst);\n+\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, \u0026rt-\u003edst);\n \ttreq-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n \n \tret = tcp_get_cookie_sock(sk, skb, req, \u0026rt-\u003edst);\ndiff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c\nindex 1c867a3024446..fb376a97f0e6d 100644\n--- a/net/ipv4/tcp.c\n+++ b/net/ipv4/tcp.c\n@@ -463,6 +463,8 @@ void tcp_init_sock(struct sock sk)\n \n \ttp-\u003etsoffset = 0;\n \ttp-\u003erack.reo_wnd_steps = 1;\n+\ttp-\u003eecn_mode = TCP_ECN_MODE_UNSPEC;\n+\ttp-\u003eecn_option = TCP_ACCECN_OPTION_UNSPEC;\n \n \tsk-\u003esk_write_space = sk_stream_write_space;\n \tsock_set_flag(sk, SOCK_USE_WRITE_QUEUE);\n@@ -4160,6 +4162,18 @@ int do_tcp_setsockopt(struct sock sk, int level, int optname,\n \t\ttcp_enable_tx_delay(sk, val);\n \t\tWRITE_ONCE(tp-\u003etcp_tx_delay, val);\n \t\tbreak;\n+\tcase TCP_ECN:\n+\t\tif (val != TCP_ECN_MODE_UNSPEC \u0026\u0026 (val \u003c 0 \|\| val \u003e TCP_ECN_IN_ACCECN_OUT_NOECN))\n+\t\t\terr = -EINVAL;\n+\t\telse\n+\t\t\tWRITE_ONCE(tp-\u003eecn_mode, val);\n+\t\tbreak;\n+\tcase TCP_ECN_OPTION:\n+\t\tif (val != TCP_ACCECN_OPTION_UNSPEC \u0026\u0026 (val \u003c 0 \|\| val \u003e TCP_ACCECN_OPTION_PERSIST))\n+\t\t\terr = -EINVAL;\n+\t\telse\n+\t\t\tWRITE_ONCE(tp-\u003eecn_option, val);\n+\t\tbreak;\n \tdefault:\n \t\terr = -ENOPROTOOPT;\n \t\tbreak;\n@@ -4842,6 +4856,12 @@ int do_tcp_getsockopt(struct sock sk, int level,\n \tcase TCP_DELACK_MAX_US:\n \t\tval = jiffies_to_usecs(READ_ONCE(inet_csk(sk)-\u003eicsk_delack_max));\n \t\tbreak;\n+\tcase TCP_ECN:\n+\t\tval = READ_ONCE(tp-\u003eecn_mode);\n+\t\tbreak;\n+\tcase TCP_ECN_OPTION:\n+\t\tval = READ_ONCE(tp-\u003eecn_option);\n+\t\tbreak;\n \tdefault:\n \t\treturn -ENOPROTOOPT;\n \t}\n@@ -5256,6 +5276,8 @@ static void __init tcp_struct_check(void)\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, tsorted_sent_queue);\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, highest_sack);\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_flags);\n+\tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_mode);\n+\tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_option);\n \n \t/* TXRX read-write hotpath cache lines /\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, pred_flags);\ndiff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c\nindex 0f60a1dbf9274..0043b4b2bc922 100644\n--- a/net/ipv4/tcp_input.c\n+++ b/net/ipv4/tcp_input.c\n@@ -7457,13 +7457,12 @@ static void tcp_ecn_create_request(struct request_sock req,\n \t\t\t\t const struct dst_entry dst)\n {\n \tconst struct tcphdr th = tcp_hdr(skb);\n-\tconst struct net net = sock_net(listen_sk);\n \tbool th_ecn = th-\u003eece \u0026\u0026 th-\u003ecwr;\n \tbool ect, ecn_ok;\n \tu32 ecn_ok_dst;\n \n \tif (tcp_accecn_syn_requested(th) \u0026\u0026\n-\t (READ_ONCE(net-\u003eipv4.sysctl_tcp_ecn) \u003e= 3 \|\|\n+\t (tcp_ecn_mode_eff(listen_sk) \u003e= 3 \|\|\n \t tcp_ca_needs_accecn(listen_sk))) {\n \t\tinet_rsk(req)-\u003eecn_ok = 1;\n \t\ttcp_rsk(req)-\u003eaccecn_ok = 1;\n@@ -7477,7 +7476,7 @@ static void tcp_ecn_create_request(struct request_sock req,\n \n \tect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)-\u003eip_dsfield);\n \tecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);\n-\tecn_ok = READ_ONCE(net-\u003eipv4.sysctl_tcp_ecn) \|\| ecn_ok_dst;\n+\tecn_ok = tcp_ecn_mode_eff(listen_sk) \|\| ecn_ok_dst;\n \n \tif (((!ect \|\| th-\u003eres1 \|\| th-\u003eae) \u0026\u0026 ecn_ok) \|\|\n \t tcp_ca_needs_ecn(listen_sk) \|\|\ndiff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c\nindex 00417a4292225..82b96c4015fd0 100644\n--- a/net/ipv4/tcp_output.c\n+++ b/net/ipv4/tcp_output.c\n@@ -1045,7 +1045,7 @@ static unsigned int tcp_syn_options(struct sock sk, struct sk_buff skb,\n \tif (unlikely((TCP_SKB_CB(skb)-\u003etcp_flags \u0026 TCPHDR_ACK) \u0026\u0026\n \t\t tcp_ecn_mode_accecn(tp) \u0026\u0026\n \t\t inet_csk(sk)-\u003eicsk_retransmits \u003c 2 \u0026\u0026\n-\t\t READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn_option) \u0026\u0026\n+\t\t tcp_accecn_option_eff(sk) \u0026\u0026\n \t\t remaining \u003e= TCPOLEN_ACCECN_BASE)) {\n \t\topts-\u003euse_synack_ecn_bytes = 1;\n \t\tremaining -= tcp_options_fit_accecn(opts, 0, remaining);\n@@ -1133,7 +1133,7 @@ static unsigned int tcp_synack_options(const struct sock sk,\n \tsmc_set_option_cond(tcp_sk(sk), ireq, opts, \u0026remaining);\n \n \tif (treq-\u003eaccecn_ok \u0026\u0026\n-\t READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn_option) \u0026\u0026\n+\t tcp_accecn_option_eff(sk) \u0026\u0026\n \t synack_type != TCP_SYNACK_RETRANS \u0026\u0026 remaining \u003e= TCPOLEN_ACCECN_BASE) {\n \t\topts-\u003euse_synack_ecn_bytes = 1;\n \t\tremaining -= tcp_options_fit_accecn(opts, 0, remaining);\n@@ -1221,7 +1221,7 @@ static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb\n \t}\n \n \tif (tcp_ecn_mode_accecn(tp)) {\n-\t\tint ecn_opt = READ_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_ecn_option);\n+\t\tint ecn_opt = tcp_accecn_option_eff(sk);\n \n \t\tif (ecn_opt \u0026\u0026 tp-\u003esaw_accecn_opt \u0026\u0026\n \t\t (ecn_opt \u003e= TCP_ACCECN_OPTION_PERSIST \|\|\ndiff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c\nindex b581cb1ee2e8a..06efcbf463467 100644\n--- a/net/ipv6/syncookies.c\n+++ b/net/ipv6/syncookies.c\n@@ -271,7 +271,7 @@ struct sock cookie_v6_check(struct sock sk, struct sk_buff skb)\n \t /\n \tif (!req-\u003esyncookie)\n \t\tireq-\u003ercv_wscale = rcv_wscale;\n-\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(net, dst);\n+\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, dst);\n \ttcp_rsk(req)-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n \n \tret = tcp_get_cookie_sock(sk, skb, req, dst);\ndiff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h\nindex 732b35cc08d1c..c58b1633bb46e 100644\n--- a/tools/include/uapi/linux/bpf.h\n+++ b/tools/include/uapi/linux/bpf.h\n@@ -2985,7 +2985,8 @@ union bpf_attr {\n \t\t TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT,\n * \t\t TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP,\n * \t\t TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX,\n- \t\t TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS.\n+ \t\t TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS,\n+ \t\t TCP_ECN, TCP_ECN_OPTION.\n \t\t* IPPROTO_IP, which supports optname IP_TOS.\n * \t\t* IPPROTO_IPV6, which supports the following optname\\ s:\n * \t\t IPV6_TCLASS, IPV6_AUTOFLOWLABEL.\ndiff --git a/tools/include/uapi/linux/tcp.h b/tools/include/uapi/linux/tcp.h\nindex 13ceeb395eb8f..4f52b9df42661 100644\n--- a/tools/include/uapi/linux/tcp.h\n+++ b/tools/include/uapi/linux/tcp.h\n@@ -128,7 +128,8 @@ enum {\n #define TCP_CM_INQ\t\tTCP_INQ\n \n #define TCP_TX_DELAY\t\t37\t/* delay outgoing packets by XX usec /\n-\n+#define TCP_ECN\t\t\t47\t/ Per-socket ECN mode (0-5, 255=use sysctl) /\n+#define TCP_ECN_OPTION\t\t48\t/ Per-socket AccECN option (0-3, 255=use sysctl) */\n \n #define TCP_REPAIR_ON\t\t1\n #define TCP_REPAIR_OFF\t\t0\ndiff --git a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h\nindex 593b38f904174..8d6ee2411db86 100644\n--- a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h\n+++ b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h\n@@ -59,6 +59,8 @@\n #define TCP_CA_NAME_MAX\t\t16\n #define TCP_NAGLE_OFF\t\t1\n #define TCP_RTO_MAX_MS\t\t44\n+#define TCP_ECN\t\t\t47\n+#define TCP_ECN_OPTION\t\t48\n \n #define TCP_ECN_OK 1\n #define TCP_ECN_QUEUE_CWR 2\ndiff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c b/tools/testing/selftests/bpf/progs/setget_sockopt.c\nindex d96e99b67aebf..fb97fa0bc7b47 100644\n--- a/tools/testing/selftests/bpf/progs/setget_sockopt.c\n+++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c\n@@ -64,6 +64,8 @@ static const struct sockopt_test sol_tcp_tests[] = {\n \t{ .opt = TCP_BPF_DELACK_MAX, .new = 30000, .expected = 30000, },\n \t{ .opt = TCP_BPF_RTO_MIN, .new = 30000, .expected = 30000, },\n \t{ .opt = TCP_RTO_MAX_MS, .new = 2000, .expected = 2000, },\n+\t{ .opt = TCP_ECN, .new = 3, .expected = 3, .restore = 255, },\n+\t{ .opt = TCP_ECN_OPTION, .new = 2, .expected = 2, .restore = 255, },\n \t{ .opt = 0, },\n };\n \n" }
2/1	2026/09/17 15:00	agent	patch-evaluator	13m Model: core Args: null Results: { "EnableConfigs": [ "INET", "IPV6", "SYN_COOKIES", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "sol_tcp_sockopt", "tcp_ecn_create_request", "tcp_syn_options", "tcp_synack_options", "tcp_established_options", "cookie_v4_check", "cookie_v6_check" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options (and BPF sockopt support) allowing per-socket overrides for ECN and AccECN behavior. It alters TCP socket option handling, option formatting in SYN/SYN-ACK/established packets, SYN cookie processing, and connection request creation in reachable core networking code.", "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 5284afe60b184262a326325db48301b3fe54f95a Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 17 14:59:59 2026 +0000 syz-cluster: applied patch under review diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 208f46967ee59..2e55d9e2eb09a 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -528,6 +528,43 @@ tcp_ecn_fallback - BOOLEAN Default: 1 (enabled) +tcp_ecn (socket option) - TCP_ECN + Per-socket control of ECN mode, allowing per-connection override of the + tcp_ecn sysctl setting. This enables L4S (Low Latency, Low Loss, Scalable + Throughput) configuration on a per-socket basis. + + Setting this socket option to any value except 255 will override the + system-wide tcp_ecn sysctl for that particular socket. A value of 255 + (TCP_ECN_MODE_UNSPEC) means use the system default sysctl value. + + Possible values: 0-5 (see tcp_ecn sysctl description above), or 255 to + use the system default (sysctl_tcp_ecn). + + Example:: + + int val = 3; /* AccECN mode / + setsockopt(fd, SOL_TCP, TCP_ECN, &val, sizeof(val)); + + Default: 255 (unspecified - uses tcp_ecn sysctl value) + +tcp_ecn_option (socket option) - TCP_ECN_OPTION + Per-socket control of Accurate ECN (AccECN) option sending behavior, + allowing per-connection override of the tcp_ecn_option sysctl setting. + + Setting this socket option to any value except 255 will override the + system-wide tcp_ecn_option sysctl for that particular socket. A value of + 255 (TCP_ACCECN_OPTION_UNSPEC) means use the system default sysctl value. + + Possible values: 0-3 (see tcp_ecn_option sysctl description above), or 255 + to use the system default (sysctl_tcp_ecn_option). + + Example:: + + int val = 2; / Send AccECN option on every packet / + setsockopt(fd, SOL_TCP, TCP_ECN_OPTION, &val, sizeof(val)); + + Default: 255 (unspecified - uses tcp_ecn_option sysctl value) + tcp_fack - BOOLEAN This is a legacy option, it has no effect anymore. diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 6a8c77719322f..7cb1e765f4618 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -289,6 +289,13 @@ struct tcp_sock { sacked_out > 0) / u8 ecn_flags; / ECN status bits. / + u8 ecn_mode; / Per-socket ECN mode override + * (TCP_ECN_MODE_UNSPEC = use sysctl) + / + u8 ecn_option; / Per-socket AccECN option override + * (TCP_ACCECN_OPTION_UNSPEC = use sysctl) + / + __cacheline_group_end(tcp_sock_write_tx); / TXRX read-write hotpath cache lines / diff --git a/include/net/tcp.h b/include/net/tcp.h index 5e5f5f9b89a38..b7c0b519ac078 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -707,12 +707,6 @@ u64 cookie_init_timestamp(struct request_sock req, u64 now); bool cookie_timestamp_decode(const struct net net, struct tcp_options_received opt); -static inline bool cookie_ecn_ok(const struct net net, const struct dst_entry dst) -{ - return READ_ONCE(net->ipv4.sysctl_tcp_ecn) \|\| - dst_feature(dst, RTAX_FEATURE_ECN); -} - #if IS_ENABLED(CONFIG_BPF) static inline bool cookie_bpf_ok(struct sk_buff skb) { diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index 865d5c5a7718d..48e364c458b29 100644 --- a/include/net/tcp_ecn.h +++ b/include/net/tcp_ecn.h @@ -22,6 +22,7 @@ enum tcp_ecn_mode { TCP_ECN_IN_ACCECN_OUT_ACCECN = 3, TCP_ECN_IN_ACCECN_OUT_ECN = 4, TCP_ECN_IN_ACCECN_OUT_NOECN = 5, + TCP_ECN_MODE_UNSPEC = 255, / Use sysctl default (per-socket) / }; / AccECN option sending when AccECN has been successfully negotiated / @@ -30,8 +31,36 @@ enum tcp_accecn_option { TCP_ACCECN_OPTION_MINIMUM = 1, TCP_ACCECN_OPTION_FULL = 2, TCP_ACCECN_OPTION_PERSIST = 3, + TCP_ACCECN_OPTION_UNSPEC = 255, / Use sysctl default (per-socket) / }; +/ Resolve the effective ECN mode: per-socket override or sysctl fallback / +static inline u8 tcp_ecn_mode_eff(const struct sock sk) +{ + u8 mode = READ_ONCE(tcp_sk(sk)->ecn_mode); + + if (mode == TCP_ECN_MODE_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn); + return mode; +} + +/* Resolve the effective AccECN option: per-socket override or sysctl fallback / +static inline u8 tcp_accecn_option_eff(const struct sock sk) +{ + u8 opt = READ_ONCE(tcp_sk(sk)->ecn_option); + + if (opt == TCP_ACCECN_OPTION_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + return opt; +} + +/* ECN support for SYN cookies: per-socket override or route feature / +static inline bool cookie_ecn_ok(const struct sock sk, const struct dst_entry dst) +{ + return tcp_ecn_mode_eff(sk) \|\| + dst_feature(dst, RTAX_FEATURE_ECN); +} + / Apply either ECT(0) or ECT(1) based on TCP_CONG_ECT_1_NEGOTIATION flag / static inline void INET_ECN_xmit_ect_1_negotiation(struct sock sk) { @@ -599,7 +628,7 @@ static inline void tcp_ecn_send_syn(struct sock sk, struct sk_buff skb) struct tcp_sock tp = tcp_sk(sk); bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk); bool use_ecn, use_accecn; - u8 tcp_ecn = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn); + u8 tcp_ecn = tcp_ecn_mode_eff(sk); use_accecn = tcp_ecn == TCP_ECN_IN_ACCECN_OUT_ACCECN \|\| tcp_ca_needs_accecn(sk); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 732b35cc08d1c..c58b1633bb46e 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2985,7 +2985,8 @@ union bpf_attr { TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT, * TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP, * TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX, - * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS. + * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS, + * TCP_ECN, TCP_ECN_OPTION. * * IPPROTO_IP, which supports optname IP_TOS. * * IPPROTO_IPV6, which supports the following optname\ s: * IPV6_TCLASS, IPV6_AUTOFLOWLABEL. diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index 03772dd4d3992..01ebb348ba274 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -142,6 +142,8 @@ enum { #define TCP_RTO_MAX_MS 44 /* max rto time in ms / #define TCP_RTO_MIN_US 45 / min rto time in us / #define TCP_DELACK_MAX_US 46 / max delayed ack time in us / +#define TCP_ECN 47 / Per-socket ECN mode (0-5, 255=use sysctl) / +#define TCP_ECN_OPTION 48 / Per-socket AccECN option (0-3, 255=use sysctl) / #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/net/core/filter.c b/net/core/filter.c index 61940e7535523..993b31e10b944 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5670,6 +5670,8 @@ static int sol_tcp_sockopt(struct sock sk, int optname, case TCP_NOTSENT_LOWAT: case TCP_SAVE_SYN: case TCP_RTO_MAX_MS: + case TCP_ECN: + case TCP_ECN_OPTION: if (optlen != sizeof(int)) return -EINVAL; break; diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 73e1297681847..ebc438bc6a461 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -490,7 +490,7 @@ struct sock cookie_v4_check(struct sock sk, struct sk_buff skb) / if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; - ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst); + ireq->ecn_ok &= cookie_ecn_ok(sk, &rt->dst); treq->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst); diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 1c867a3024446..fb376a97f0e6d 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -463,6 +463,8 @@ void tcp_init_sock(struct sock sk) tp->tsoffset = 0; tp->rack.reo_wnd_steps = 1; + tp->ecn_mode = TCP_ECN_MODE_UNSPEC; + tp->ecn_option = TCP_ACCECN_OPTION_UNSPEC; sk->sk_write_space = sk_stream_write_space; sock_set_flag(sk, SOCK_USE_WRITE_QUEUE); @@ -4160,6 +4162,18 @@ int do_tcp_setsockopt(struct sock sk, int level, int optname, tcp_enable_tx_delay(sk, val); WRITE_ONCE(tp->tcp_tx_delay, val); break; + case TCP_ECN: + if (val != TCP_ECN_MODE_UNSPEC && (val < 0 \|\| val > TCP_ECN_IN_ACCECN_OUT_NOECN)) + err = -EINVAL; + else + WRITE_ONCE(tp->ecn_mode, val); + break; + case TCP_ECN_OPTION: + if (val != TCP_ACCECN_OPTION_UNSPEC && (val < 0 \|\| val > TCP_ACCECN_OPTION_PERSIST)) + err = -EINVAL; + else + WRITE_ONCE(tp->ecn_option, val); + break; default: err = -ENOPROTOOPT; break; @@ -4842,6 +4856,12 @@ int do_tcp_getsockopt(struct sock sk, int level, case TCP_DELACK_MAX_US: val = jiffies_to_usecs(READ_ONCE(inet_csk(sk)->icsk_delack_max)); break; + case TCP_ECN: + val = READ_ONCE(tp->ecn_mode); + break; + case TCP_ECN_OPTION: + val = READ_ONCE(tp->ecn_option); + break; default: return -ENOPROTOOPT; } @@ -5256,6 +5276,8 @@ static void __init tcp_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, tsorted_sent_queue); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, highest_sack); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_flags); + CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_mode); + CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_option); /* TXRX read-write hotpath cache lines / CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, pred_flags); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 0f60a1dbf9274..0043b4b2bc922 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -7457,13 +7457,12 @@ static void tcp_ecn_create_request(struct request_sock req, const struct dst_entry dst) { const struct tcphdr th = tcp_hdr(skb); - const struct net net = sock_net(listen_sk); bool th_ecn = th->ece && th->cwr; bool ect, ecn_ok; u32 ecn_ok_dst; if (tcp_accecn_syn_requested(th) && - (READ_ONCE(net->ipv4.sysctl_tcp_ecn) >= 3 \|\| + (tcp_ecn_mode_eff(listen_sk) >= 3 \|\| tcp_ca_needs_accecn(listen_sk))) { inet_rsk(req)->ecn_ok = 1; tcp_rsk(req)->accecn_ok = 1; @@ -7477,7 +7476,7 @@ static void tcp_ecn_create_request(struct request_sock req, ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield); ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK); - ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) \|\| ecn_ok_dst; + ecn_ok = tcp_ecn_mode_eff(listen_sk) \|\| ecn_ok_dst; if (((!ect \|\| th->res1 \|\| th->ae) && ecn_ok) \|\| tcp_ca_needs_ecn(listen_sk) \|\| diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 00417a4292225..82b96c4015fd0 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1045,7 +1045,7 @@ static unsigned int tcp_syn_options(struct sock sk, struct sk_buff skb, if (unlikely((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK) && tcp_ecn_mode_accecn(tp) && inet_csk(sk)->icsk_retransmits < 2 && - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) && + tcp_accecn_option_eff(sk) && remaining >= TCPOLEN_ACCECN_BASE)) { opts->use_synack_ecn_bytes = 1; remaining -= tcp_options_fit_accecn(opts, 0, remaining); @@ -1133,7 +1133,7 @@ static unsigned int tcp_synack_options(const struct sock sk, smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining); if (treq->accecn_ok && - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) && + tcp_accecn_option_eff(sk) && synack_type != TCP_SYNACK_RETRANS && remaining >= TCPOLEN_ACCECN_BASE) { opts->use_synack_ecn_bytes = 1; remaining -= tcp_options_fit_accecn(opts, 0, remaining); @@ -1221,7 +1221,7 @@ static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb } if (tcp_ecn_mode_accecn(tp)) { - int ecn_opt = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + int ecn_opt = tcp_accecn_option_eff(sk); if (ecn_opt && tp->saw_accecn_opt && (ecn_opt >= TCP_ACCECN_OPTION_PERSIST \|\| diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c index b581cb1ee2e8a..06efcbf463467 100644 --- a/net/ipv6/syncookies.c +++ b/net/ipv6/syncookies.c @@ -271,7 +271,7 @@ struct sock cookie_v6_check(struct sock sk, struct sk_buff skb) / if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; - ireq->ecn_ok &= cookie_ecn_ok(net, dst); + ireq->ecn_ok &= cookie_ecn_ok(sk, dst); tcp_rsk(req)->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, dst); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 732b35cc08d1c..c58b1633bb46e 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -2985,7 +2985,8 @@ union bpf_attr { TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT, * TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP, * TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX, - * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS. + * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS, + * TCP_ECN, TCP_ECN_OPTION. * * IPPROTO_IP, which supports optname IP_TOS. * * IPPROTO_IPV6, which supports the following optname\ s: * IPV6_TCLASS, IPV6_AUTOFLOWLABEL. diff --git a/tools/include/uapi/linux/tcp.h b/tools/include/uapi/linux/tcp.h index 13ceeb395eb8f..4f52b9df42661 100644 --- a/tools/include/uapi/linux/tcp.h +++ b/tools/include/uapi/linux/tcp.h @@ -128,7 +128,8 @@ enum { #define TCP_CM_INQ TCP_INQ #define TCP_TX_DELAY 37 /* delay outgoing packets by XX usec / - +#define TCP_ECN 47 / Per-socket ECN mode (0-5, 255=use sysctl) / +#define TCP_ECN_OPTION 48 / Per-socket AccECN option (0-3, 255=use sysctl) */ #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h index 593b38f904174..8d6ee2411db86 100644 --- a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h +++ b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h @@ -59,6 +59,8 @@ #define TCP_CA_NAME_MAX 16 #define TCP_NAGLE_OFF 1 #define TCP_RTO_MAX_MS 44 +#define TCP_ECN 47 +#define TCP_ECN_OPTION 48 #define TCP_ECN_OK 1 #define TCP_ECN_QUEUE_CWR 2 diff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c b/tools/testing/selftests/bpf/progs/setget_sockopt.c index d96e99b67aebf..fb97fa0bc7b47 100644 --- a/tools/testing/selftests/bpf/progs/setget_sockopt.c +++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c @@ -64,6 +64,8 @@ static const struct sockopt_test sol_tcp_tests[] = { { .opt = TCP_BPF_DELACK_MAX, .new = 30000, .expected = 30000, }, { .opt = TCP_BPF_RTO_MIN, .new = 30000, .expected = 30000, }, { .opt = TCP_RTO_MAX_MS, .new = 2000, .expected = 2000, }, + { .opt = TCP_ECN, .new = 3, .expected = 3, .restore = 255, }, + { .opt = TCP_ECN_OPTION, .new = 2, .expected = 2, .restore = 255, }, { .opt = 0, }, };
3/2	2026/09/17 15:00	llm	patch-evaluator	12m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9385 output: 22 thoughts: 1304 Thoughts: Analyzing the Patch for Fuzzing Potential Okay, let's break this down. The patch introduces new socket options for TCP, namely `TCP_ECN` and `TCP_ECN_OPTION`. My initial thought is to evaluate if this warrants fuzzing with syzkaller, and I think it does. First, I reviewed the code. This patch modifies core areas like the TCP stack, sysctl interface, socket options (`setsockopt`, `getsockopt`), the TCP handshake process, SYN cookies, options negotiation, and BPF sockopt support. It touches fundamental networking components, indicating substantial reachability. This means it is definitely "WorthFuzzing" according to the rules! Now, let's confirm this using the WorthFuzzing rules. The patch alters reachable executable code, hitting core networking components and the socket API. Specifically: * It modifies logic within core networking. * It is introducing new socket options. * It alters data structures (adding `ecn_mode` and `ecn_option` to `struct tcp_sock`). Therefore, WorthFuzzing = true is confirmed. Next, I need to define the FocusSymbols. I'm going to follow the guidance to avoid ubiquitous lifecycle hot-paths and target specific feature logic and entry points. Looking at the changes, I see these functions are directly modified or affected: * `do_tcp_setsockopt` * `do_tcp_getsockopt` * `tcp_ecn_create_request` * `cookie_v4_check` * `cookie_v6_check` * `tcp_syn_options` * `tcp_synack_options` * `tcp_established_options` * `sol_tcp_sockopt` * `tcp_init_sock` * And the static inline functions in `tcp_ecn.h`: * `tcp_ecn_mode_eff` * `tcp_accecn_option_eff` * `cookie_ecn_ok` * `tcp_ecn_send_syn` Now, I need to check the rules about the static inline functions. Since the changes impact static inline helpers, I will identify specific non-static, feature-specific caller functions in `.c` files to exercise them, avoiding ubiquitous lifecycle wrappers. Specifically, let's see where the `tcp_ecn_send_syn` is called!
4/2	2026/09/17 15:12	tool	grepper	0m Args: { "Expression": "tcp_ecn_send_syn" } Results: { "Output": "include/net/tcp_ecn.h=597=static inline bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock tp,\n--\ninclude/net/tcp_ecn.h-605-/ Packet ECN state for a SYN-ACK /\ninclude/net/tcp_ecn.h:606:static inline void tcp_ecn_send_synack(struct sock sk, struct sk_buff skb)\ninclude/net/tcp_ecn.h-607-{\n--\ninclude/net/tcp_ecn.h-625-/ Packet ECN state for a SYN. /\ninclude/net/tcp_ecn.h:626:static inline void tcp_ecn_send_syn(struct sock sk, struct sk_buff skb)\ninclude/net/tcp_ecn.h-627-{\n--\nnet/ipv4/tcp_output.c=3895=int tcp_send_synack(struct sock sk)\n--\nnet/ipv4/tcp_output.c-3923-\t\tTCP_SKB_CB(skb)-\u003etcp_flags \|= TCPHDR_ACK;\nnet/ipv4/tcp_output.c:3924:\t\ttcp_ecn_send_synack(sk, skb);\nnet/ipv4/tcp_output.c-3925-\t}\n--\nnet/ipv4/tcp_output.c=4306=int tcp_connect(struct sock *sk)\n--\nnet/ipv4/tcp_output.c-4385-\ttcp_connect_queue_skb(sk, buff);\nnet/ipv4/tcp_output.c:4386:\ttcp_ecn_send_syn(sk, buff);\nnet/ipv4/tcp_output.c-4387-\ttcp_rbtree_insert(\u0026sk-\u003etcp_rtx_queue, buff);\n" }
5/2	2026/09/17 15:12	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11733 output: 22 thoughts: 38 Thoughts: Here's my thought process, as if I were analyzing this code: Analyzing the ECN SYN Handshake Okay, so `tcp_ecn_send_syn` is definitely called right in `tcp_connect`. That makes sense; we want to establish ECN capability right from the start of the connection. Now, the question is, where does `tcp_ecn_create_request` come into play? It's crucial to understand the whole ECN handshake initiation flow. I need to trace back from that function and see what's triggering its execution. Let's dig into the code and find the call sites for `tcp_ecn_create_request`. I need to figure out when this request is built, and what the dependencies are.
6/2	2026/09/17 15:12	tool	grepper	0m Args: { "Expression": "tcp_ecn_create_request" } Results: { "Output": "net/ipv4/tcp_input.c=7423=static inline void pr_drop_req(struct request_sock req, __u16 port, int family)\n--\nnet/ipv4/tcp_input.c-7453- /\nnet/ipv4/tcp_input.c:7454:static void tcp_ecn_create_request(struct request_sock req,\nnet/ipv4/tcp_input.c-7455-\t\t\t\t const struct sk_buff skb,\n--\nnet/ipv4/tcp_input.c=7619=int tcp_conn_request(struct request_sock_ops *rsk_ops,\n--\nnet/ipv4/tcp_input.c-7736-\nnet/ipv4/tcp_input.c:7737:\ttcp_ecn_create_request(req, skb, sk, dst);\nnet/ipv4/tcp_input.c-7738-\n" }
7/2	2026/09/17 15:12	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 12204 output: 33 thoughts: 47 Thoughts: Okay, here's my take on those thoughts, framed as my own: Analyzing TCP Option Handling Alright, I need to get a handle on how TCP options are handled. I'm wondering if the option configurations for SYN, SYN-ACK, and established connections are static. To figure this out, my first stop has to be `net/ipv4/tcp_output.c`. That's where the core TCP output logic lives, and where I expect to find the code responsible for constructing the TCP headers, including the options fields, during connection establishment and subsequent data transmission. I need to dig into that file and see how these different option sets are managed. Is it all hardcoded? Or are there dynamic elements, perhaps configuration variables that influence the options sent? Time to dive in.
8/2	2026/09/17 15:12	tool	grepper	0m Args: { "Expression": "tcp_syn(ack)?_options", "PathPrefix": "net/ipv4/" } Results: { "Output": "net/ipv4/tcp_ao.c=1384=static int tcp_ao_parse_crypto(const struct tcp_ao_add cmd,\n--\nnet/ipv4/tcp_ao.c-1393-\t \t\t\t\t\t- wscale),\nnet/ipv4/tcp_ao.c:1394:\t * see tcp_syn_options(), tcp_synack_options(), commit 33ad798c924b.\nnet/ipv4/tcp_ao.c-1395-\t \n--\nnet/ipv4/tcp_output.c=866=static void mptcp_set_option_cond(const struct request_sock req,\n--\nnet/ipv4/tcp_output.c-872-\nnet/ipv4/tcp_output.c:873:\t\tif (mptcp_synack_options(req, \u0026size, \u0026opts-\u003emptcp)) {\nnet/ipv4/tcp_output.c-874-\t\t\tif (remaining \u003e= size) {\n--\nnet/ipv4/tcp_output.c-881-\nnet/ipv4/tcp_output.c:882:static u32 tcp_synack_options_combine_saving(struct tcp_out_options opts)\nnet/ipv4/tcp_output.c-883-{\n--\nnet/ipv4/tcp_output.c=903=static int tcp_options_fit_accecn(struct tcp_out_options opts, int required,\n--\nnet/ipv4/tcp_output.c-912-\tif (opts-\u003euse_synack_ecn_bytes)\nnet/ipv4/tcp_output.c:913:\t\tmax_combine_saving = tcp_synack_options_combine_saving(opts);\nnet/ipv4/tcp_output.c-914-\telse\n--\nnet/ipv4/tcp_output.c-958- /\nnet/ipv4/tcp_output.c:959:static unsigned int tcp_syn_options(struct sock sk, struct sk_buff skb,\nnet/ipv4/tcp_output.c-960-\t\t\t\tstruct tcp_out_options opts,\n--\nnet/ipv4/tcp_output.c-1031-\nnet/ipv4/tcp_output.c:1032:\t\tif (mptcp_syn_options(sk, skb, \u0026size, \u0026opts-\u003emptcp)) {\nnet/ipv4/tcp_output.c-1033-\t\t\tif (remaining \u003e= size) {\n--\nnet/ipv4/tcp_output.c-1060-/ Set up TCP options for SYN-ACKs. /\nnet/ipv4/tcp_output.c:1061:static unsigned int tcp_synack_options(const struct sock sk,\nnet/ipv4/tcp_output.c-1062-\t\t\t\t struct request_sock req,\n--\nnet/ipv4/tcp_output.c=1536=static int __tcp_transmit_skb(struct sock sk, struct sk_buff skb,\n--\nnet/ipv4/tcp_output.c-1579-\tif (unlikely(tcb-\u003etcp_flags \u0026 TCPHDR_SYN)) {\nnet/ipv4/tcp_output.c:1580:\t\ttcp_options_size = tcp_syn_options(sk, skb, \u0026opts, \u0026key);\nnet/ipv4/tcp_output.c-1581-\t} else {\n--\nnet/ipv4/tcp_output.c=3939=struct sk_buff tcp_make_synack(const struct sock sk, struct dst_entry dst,\n--\nnet/ipv4/tcp_output.c-4036-\tTCP_SKB_CB(skb)-\u003etcp_flags = TCPHDR_SYN \| TCPHDR_ACK;\nnet/ipv4/tcp_output.c:4037:\ttcp_header_size = tcp_synack_options(sk, req, mss, skb, \u0026opts,\nnet/ipv4/tcp_output.c-4038-\t\t\t\t\t \u0026key, foc, synack_type, syn_skb)\n" }
9/2	2026/09/17 15:12	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13483 output: 25 thoughts: 1076 Thoughts: Analyzing the ECN Patch's Scope and Implementation Okay, let's break this down. First, I need to understand which functions are central to this ECN-related patch. I'm seeing `tcp_syn_options`, `tcp_synack_options`, and `tcp_established_options` as static in `tcp_output.c`. Wait, `tcp_synack_options` is called by `tcp_make_synack`, which is non-static, so it's a candidate. However, static functions are usually fine, but I should consult the prompt instructions. Ah, the instructions say to identify non-static callers for static helpers; that's the key. The patch itself appears to modify several key areas. Specifically, the patch touches `do_tcp_setsockopt` and `do_tcp_getsockopt` in `net/ipv4/tcp.c`, implementing `setsockopt` and `getsockopt` functionality for `TCP_ECN` and `TCP_ECN_OPTION`. There's also `sol_tcp_sockopt` in `net/core/filter.c` related to BPF sockopt, and `cookie_v4_check` and `cookie_v6_check` in the syncookies code. Crucially, the patch involves `tcp_make_synack` in `tcp_output.c`, which is the direct caller of the static `tcp_synack_options`. I should not forget about `tcp_connect` which calls `tcp_ecn_send_syn` and `tcp_conn_request` which calls `tcp_ecn_create_request`, which are also in `tcp_output.c` and `tcp_input.c` respectively. Now, I'm going to look at `do_tcp_setsockopt` closely, since it's directly modified. Looking at the code for `do_tcp_setsockopt`, I see the implementation for `TCP_ECN` and `TCP_ECN_OPTION`. It correctly handles the range checks for the values provided to these sockopts: ```c case TCP_ECN: if (val != TCP_ECN_MODE_UNSPEC && (val < 0 \|\| val > TCP_ECN_IN_ACCECN_OUT_NOECN)) err = -EINVAL; else WRITE_ONCE(tp->ecn_mode, val); break; case TCP_ECN_OPTION: if (val != TCP_ACCECN_OPTION_UNSPEC && (val < 0 \|\| val > TCP_ACCECN_OPTION_PERSIST)) err = -EINVAL; else WRITE_ONCE(tp->ecn_option, val); break; ``` And `do_tcp_getsockopt`: ```c case TCP_ECN: val = READ_ONCE(tp->ecn_mode); break; case TCP_ECN_OPTION: val = READ_ONCE(tp->ecn_option); break; ``` And finally `sol_tcp_sockopt`, ensuring correct option length for BPF: ```c case TCP_ECN: case TCP_ECN_OPTION: if (*optlen != sizeof(int)) return -EINVAL; break; ``` Finally, let me ensure there are no specific Kconfig dependencies. `TCP_ECN` and `TCP_ECN_OPTION` are within the TCP stack, so it's likely built under `CONFIG_INET`, which is a standard configuration. Let me just confirm that in the Kconfig files.
10/2	2026/09/17 15:13	tool	grepper	0m Args: { "Expression": "config INET", "PathPrefix": "net/" } Results: { "Output": "net/Kconfig=99=config NET_HANDSHAKE_KUNIT_TEST\n--\nnet/Kconfig-113-\nnet/Kconfig:114:config INET\nnet/Kconfig-115-\tbool \"TCP/IP networking\"\n--\nnet/ipv4/Kconfig=330=config NET_FOU_IP_TUNNELS\n--\nnet/ipv4/Kconfig-338-\nnet/ipv4/Kconfig:339:config INET_AH\nnet/ipv4/Kconfig-340-\ttristate \"IP: AH transformation\"\n--\nnet/ipv4/Kconfig-353-\nnet/ipv4/Kconfig:354:config INET_ESP\nnet/ipv4/Kconfig-355-\ttristate \"IP: ESP transformation\"\n--\nnet/ipv4/Kconfig-368-\nnet/ipv4/Kconfig:369:config INET_ESP_OFFLOAD\nnet/ipv4/Kconfig-370-\ttristate \"IP: ESP transformation offload\"\n--\nnet/ipv4/Kconfig-381-\nnet/ipv4/Kconfig:382:config INET_ESPINTCP\nnet/ipv4/Kconfig-383-\tbool \"IP: ESP in TCP encapsulation (RFC 8229)\"\n--\nnet/ipv4/Kconfig-393-\nnet/ipv4/Kconfig:394:config INET_IPCOMP\nnet/ipv4/Kconfig-395-\ttristate \"IP: IPComp transformation\"\n--\nnet/ipv4/Kconfig-403-\nnet/ipv4/Kconfig:404:config INET_TABLE_PERTURB_ORDER\nnet/ipv4/Kconfig-405-\tint \"INET: Source port perturbation table size (as power of 2)\" if EXPERT\n--\nnet/ipv4/Kconfig-413-\nnet/ipv4/Kconfig:414:config INET_XFRM_TUNNEL\nnet/ipv4/Kconfig-415-\ttristate\n--\nnet/ipv4/Kconfig-418-\nnet/ipv4/Kconfig:419:config INET_TUNNEL\nnet/ipv4/Kconfig-420-\ttristate\n--\nnet/ipv4/Kconfig-422-\nnet/ipv4/Kconfig:423:config INET_DIAG\nnet/ipv4/Kconfig-424-\ttristate \"INET: socket monitoring interface\"\n--\nnet/ipv4/Kconfig-434-\nnet/ipv4/Kconfig:435:config INET_TCP_DIAG\nnet/ipv4/Kconfig-436-\tdepends on INET_DIAG\n--\nnet/ipv4/Kconfig-438-\nnet/ipv4/Kconfig:439:config INET_UDP_DIAG\nnet/ipv4/Kconfig-440-\ttristate \"UDP: socket monitoring interface\"\n--\nnet/ipv4/Kconfig-446-\nnet/ipv4/Kconfig:447:config INET_RAW_DIAG\nnet/ipv4/Kconfig-448-\ttristate \"RAW: socket monitoring interface\"\n--\nnet/ipv4/Kconfig-454-\nnet/ipv4/Kconfig:455:config INET_DIAG_DESTROY\nnet/ipv4/Kconfig-456-\tbool \"INET: allow privileged process to administratively close sockets\"\n--\nnet/ipv6/Kconfig=39=config IPV6_OPTIMISTIC_DAD\n--\nnet/ipv6/Kconfig-46-\nnet/ipv6/Kconfig:47:config INET6_AH\nnet/ipv6/Kconfig-48-\ttristate \"IPv6: AH transformation\"\n--\nnet/ipv6/Kconfig-61-\nnet/ipv6/Kconfig:62:config INET6_ESP\nnet/ipv6/Kconfig-63-\ttristate \"IPv6: ESP transformation\"\n--\nnet/ipv6/Kconfig-76-\nnet/ipv6/Kconfig:77:config INET6_ESP_OFFLOAD\nnet/ipv6/Kconfig-78-\ttristate \"IPv6: ESP transformation offload\"\n--\nnet/ipv6/Kconfig-89-\nnet/ipv6/Kconfig:90:config INET6_ESPINTCP\nnet/ipv6/Kconfig-91-\tbool \"IPv6: ESP in TCP encapsulation (RFC 8229)\"\n--\nnet/ipv6/Kconfig-101-\nnet/ipv6/Kconfig:102:config INET6_IPCOMP\nnet/ipv6/Kconfig-103-\ttristate \"IPv6: IPComp transformation\"\n--\nnet/ipv6/Kconfig=120=config IPV6_ILA\n--\nnet/ipv6/Kconfig-140-\nnet/ipv6/Kconfig:141:config INET6_XFRM_TUNNEL\nnet/ipv6/Kconfig-142-\ttristate\n--\nnet/ipv6/Kconfig-145-\nnet/ipv6/Kconfig:146:config INET6_TUNNEL\nnet/ipv6/Kconfig-147-\ttristate\n--\nnet/mptcp/Kconfig=14=if MPTCP\nnet/mptcp/Kconfig-15-\nnet/mptcp/Kconfig:16:config INET_MPTCP_DIAG\nnet/mptcp/Kconfig-17-\tdepends on INET_DIAG\n--\nnet/psp/Kconfig-4-#\nnet/psp/Kconfig:5:config INET_PSP\nnet/psp/Kconfig-6-\tbool \"PSP Security Protocol support\"\n--\nnet/sctp/Kconfig=68=endchoice\nnet/sctp/Kconfig-69-\nnet/sctp/Kconfig:70:config INET_SCTP_DIAG\nnet/sctp/Kconfig-71-\tdepends on INET_DIAG\n" }
11/2	2026/09/17 15:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 16917 output: 26 thoughts: 15 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Checking `SYNCOOKIES` Configuration Okay, so I'm just quickly running through some potential areas where we might be seeing this behavior. Since we're dealing with network behavior, my first instinct is to double-check the `SYNCOOKIES` Kconfig option. While it's probably not the direct cause, I want to rule it out immediately, given its impact on TCP connection handling and potential for altering connection establishment behavior under load. It's a quick sanity check, and I'd hate to miss something simple that could explain this. So, let's take a look.
12/2	2026/09/17 15:13	tool	grepper	0m Args: { "Expression": "SYN_COOKIES", "PathPrefix": "net/" } Results: { "Output": "net/core/filter.c=7842=BPF_CALL_5(bpf_tcp_check_syncookie, struct sock , sk, void , iph, u32, iph_len,\n--\nnet/core/filter.c-7844-{\nnet/core/filter.c:7845:#ifdef CONFIG_SYN_COOKIES\nnet/core/filter.c-7846-\tint ret;\n--\nnet/core/filter.c=7915=BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock , sk, void , iph, u32, iph_len,\n--\nnet/core/filter.c-7917-{\nnet/core/filter.c:7918:#ifdef CONFIG_SYN_COOKIES\nnet/core/filter.c-7919-\tu32 cookie;\n--\nnet/core/filter.c-7968-\treturn -EOPNOTSUPP;\nnet/core/filter.c:7969:#endif /* CONFIG_SYN_COOKIES /\nnet/core/filter.c-7970-}\n--\nnet/core/filter.c=8275=static const struct bpf_func_proto bpf_skb_set_tstamp_proto = {\n--\nnet/core/filter.c-8283-\nnet/core/filter.c:8284:#ifdef CONFIG_SYN_COOKIES\nnet/core/filter.c-8285-BPF_CALL_3(bpf_tcp_raw_gen_syncookie_ipv4, struct iphdr , iph,\n--\nnet/core/filter.c=8376=static const struct bpf_func_proto bpf_tcp_raw_check_syncookie_ipv6_proto = {\n--\nnet/core/filter.c-8385-};\nnet/core/filter.c:8386:#endif /* CONFIG_SYN_COOKIES /\nnet/core/filter.c-8387-\n--\nnet/core/filter.c=8624=tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog prog)\n--\nnet/core/filter.c-8743-\t\treturn \u0026bpf_skb_set_tstamp_proto;\nnet/core/filter.c:8744:#ifdef CONFIG_SYN_COOKIES\nnet/core/filter.c-8745-\tcase BPF_FUNC_tcp_raw_gen_syncookie_ipv4:\n--\nnet/core/filter.c=8761=xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog prog)\n--\nnet/core/filter.c-8802-\t\treturn \u0026bpf_tcp_gen_syncookie_proto;\nnet/core/filter.c:8803:#ifdef CONFIG_SYN_COOKIES\nnet/core/filter.c-8804-\tcase BPF_FUNC_tcp_raw_gen_syncookie_ipv4:\n--\nnet/core/filter.c=12507=__bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff s, struct sock sk,\n--\nnet/core/filter.c-12509-{\nnet/core/filter.c:12510:#if IS_ENABLED(CONFIG_SYN_COOKIES)\nnet/core/filter.c-12511-\tstruct sk_buff skb = (struct sk_buff )s;\n--\nnet/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--\nnet/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-$(CONFIG_INET_AH) += ah4.o\n--\nnet/ipv4/netfilter/Kconfig=207=config IP_NF_TARGET_SYNPROXY\n--\nnet/ipv4/netfilter/Kconfig-210-\tselect NETFILTER_SYNPROXY\nnet/ipv4/netfilter/Kconfig:211:\tselect SYN_COOKIES\nnet/ipv4/netfilter/Kconfig-212-\thelp\n--\nnet/ipv4/sysctl_net_ipv4.c=627=static const struct ctl_table ipv4_net_table[] = {\n--\nnet/ipv4/sysctl_net_ipv4.c-1037-\t},\nnet/ipv4/sysctl_net_ipv4.c:1038:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/sysctl_net_ipv4.c-1039-\t{\n--\nnet/ipv4/tcp_input.c=7525=static bool tcp_syn_flood_action(struct sock sk, const char proto)\n--\nnet/ipv4/tcp_input.c-7534-\nnet/ipv4/tcp_input.c:7535:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/tcp_input.c-7536-\tif (syncookies) {\n--\nnet/ipv4/tcp_ipv4.c=1636=const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {\n--\nnet/ipv4/tcp_ipv4.c-1646-#endif\nnet/ipv4/tcp_ipv4.c:1647:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/tcp_ipv4.c-1648-\t.cookie_init_seq =\tcookie_v4_init_sequence,\n--\nnet/ipv4/tcp_ipv4.c=1794=static struct sock tcp_v4_cookie_check(struct sock sk, struct sk_buff skb)\nnet/ipv4/tcp_ipv4.c-1795-{\nnet/ipv4/tcp_ipv4.c:1796:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/tcp_ipv4.c-1797-\tconst struct tcphdr th = tcp_hdr(skb);\n--\nnet/ipv4/tcp_ipv4.c=1805=u16 tcp_v4_get_syncookie(struct sock sk, struct iphdr iph,\n--\nnet/ipv4/tcp_ipv4.c-1808-\tu16 mss = 0;\nnet/ipv4/tcp_ipv4.c:1809:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/tcp_ipv4.c-1810-\tmss = tcp_get_syncookie_mss(\u0026tcp_request_sock_ops,\n--\nnet/ipv4/tcp_output.c=3939=struct sk_buff tcp_make_synack(const struct sock sk, struct dst_entry dst,\n--\nnet/ipv4/tcp_output.c-3986-\tnow = tcp_clock_ns();\nnet/ipv4/tcp_output.c:3987:#ifdef CONFIG_SYN_COOKIES\nnet/ipv4/tcp_output.c-3988-\tif (unlikely(synack_type == TCP_SYNACK_COOKIE \u0026\u0026 ireq-\u003etstamp_ok))\n--\nnet/ipv6/Makefile=22=ipv6-$(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--\nnet/ipv6/netfilter/Kconfig=221=config IP6_NF_TARGET_SYNPROXY\n--\nnet/ipv6/netfilter/Kconfig-224-\tselect NETFILTER_SYNPROXY\nnet/ipv6/netfilter/Kconfig:225:\tselect SYN_COOKIES\nnet/ipv6/netfilter/Kconfig-226-\thelp\n--\nnet/ipv6/tcp_ipv6.c=827=const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {\n--\nnet/ipv6/tcp_ipv6.c-838-#endif\nnet/ipv6/tcp_ipv6.c:839:#ifdef CONFIG_SYN_COOKIES\nnet/ipv6/tcp_ipv6.c-840-\t.cookie_init_seq =\tcookie_v6_init_sequence,\n--\nnet/ipv6/tcp_ipv6.c=1290=static struct sock tcp_v6_cookie_check(struct sock sk, struct sk_buff skb)\nnet/ipv6/tcp_ipv6.c-1291-{\nnet/ipv6/tcp_ipv6.c:1292:#ifdef CONFIG_SYN_COOKIES\nnet/ipv6/tcp_ipv6.c-1293-\tconst struct tcphdr th = tcp_hdr(skb);\n--\nnet/ipv6/tcp_ipv6.c=1301=u16 tcp_v6_get_syncookie(struct sock sk, struct ipv6hdr iph,\n--\nnet/ipv6/tcp_ipv6.c-1304-\tu16 mss = 0;\nnet/ipv6/tcp_ipv6.c:1305:#ifdef CONFIG_SYN_COOKIES\nnet/ipv6/tcp_ipv6.c-1306-\tmss = tcp_get_syncookie_mss(\u0026tcp6_request_sock_ops,\n--\nnet/mptcp/Makefile=4=mptcp-y := protocol.o subflow.o options.o token.o crypto.o ctrl.o pm.o diag.o \\\n--\nnet/mptcp/Makefile-7-\nnet/mptcp/Makefile:8:obj-$(CONFIG_SYN_COOKIES) += syncookies.o\nnet/mptcp/Makefile-9-obj-$(CONFIG_INET_MPTCP_DIAG) += mptcp_diag.o\n--\nnet/mptcp/protocol.h=1355=static inline bool subflow_simultaneous_connect(struct sock sk)\n--\nnet/mptcp/protocol.h-1362-\nnet/mptcp/protocol.h:1363:#ifdef CONFIG_SYN_COOKIES\nnet/mptcp/protocol.h-1364-void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock subflow_req,\n--\nnet/netfilter/Kconfig=649=config NFT_SYNPROXY\n--\nnet/netfilter/Kconfig-652-\tselect NETFILTER_SYNPROXY\nnet/netfilter/Kconfig:653:\tselect SYN_COOKIES\nnet/netfilter/Kconfig-654-\thelp\n" }
13/2	2026/09/17 15:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19853 output: 35 thoughts: 56 Thoughts: Examining the Kernel Configuration for SYN Cookies Okay, so I need to verify the status of `CONFIG_SYN_COOKIES`. Let's dive right into the kernel configuration files. The immediate target is `net/ipv4/Kconfig`. Ah, there it is: `SYN_COOKIES` is declared as a boolean option, and the description explicitly calls it "IP: TCP syncookie support," which is exactly what I was expecting. It's defaulting to "y" – so, enabled by default, which is pretty standard. Time to move onto the next configuration item.
14/2	2026/09/17 15:13	tool	read-file	0m Args: { "File": "net/ipv4/Kconfig", "FirstLine": 265, "LineCount": 15 } 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" }
15/2	2026/09/17 15:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 20331 output: 208 thoughts: 2072 Thoughts: Analysis of TCP ECN and AccECN Implementation for Fuzzing Focus Okay, let's break this down systematically. I need to identify the key functions and configurations related to this TCP ECN and AccECN implementation for targeted fuzzing. First, I confirmed that `CONFIG_INET` is foundational for TCP and `CONFIG_SYN_COOKIES` is necessary for SYN cookie functionality (`cookie_v4_check`, `cookie_v6_check`). The presence of `CONFIG_BPF_SYSCALL` is also essential for BPF sockopt support (`sol_tcp_sockopt`). Listing `INET`, `SYN_COOKIES` is good practice, I'll keep them in the notes. Next, I meticulously examined the code, pinpointing the functions directly modified or affected by these changes: * In `net/ipv4/tcp.c`, `do_tcp_setsockopt`, `do_tcp_getsockopt`, and `tcp_init_sock` were checked. `tcp_init_sock` is too generic and called on every TCP socket creation, a fuzzing dilution risk. However, `do_tcp_setsockopt` and `do_tcp_getsockopt` directly handle the new `TCP_ECN` and `TCP_ECN_OPTION` cases within their `switch` statements, making them specific enough. * `net/core/filter.c` includes `sol_tcp_sockopt`, modified for BPF sockopt interactions with `TCP_ECN`. * `net/ipv4/tcp_input.c`: `tcp_ecn_create_request` is called from `tcp_conn_request`. I confirmed it's a `static void` function, ensuring it's not inlined, making it a viable target. * `net/ipv4/tcp_output.c`: `tcp_syn_options`, `tcp_synack_options`, `tcp_established_options`, `tcp_connect`, and `tcp_make_synack`. * `net/ipv4/syncookies.c`: `cookie_v4_check`. * `net/ipv6/syncookies.c`: `cookie_v6_check`. I then referred to fuzzing guidelines: focusing on specific feature logic and entrypoints while avoiding ubiquitous functions or inlined static functions. Based on these guidelines, I narrowed down the focus to functions that directly implement or are entrypoints for the ECN and AccECN configurations: 1. `do_tcp_setsockopt` - Handles setting ECN options directly. 2. `do_tcp_getsockopt` - Handles getting ECN options directly. 3. `sol_tcp_sockopt` - Handles BPF sockopt for ECN. 4. `tcp_ecn_create_request` - Handles ECN request creation for incoming SYN packets. 5. `tcp_syn_options` - Generates SYN options with ECN considerations. 6. `tcp_synack_options` - Generates SYNACK options with ECN considerations. 7. `tcp_established_options` - Generates established TCP options with ECN considerations. 8. `cookie_v4_check` - Handles SYN cookie ECN checks. 9. `cookie_v6_check` - Handles SYN cookie ECN checks. These functions clearly meet the criteria: they are not ubiquitous, and are directly responsible for the new ECN/AccECN mode and option configurations during TCP handshake and option generation, syncookie validation, and socket option configuration via set/getsockopt. The essential configurations are: `INET`, `IPV6`, `SYN_COOKIES`, and `BPF_SYSCALL`. With this thorough analysis complete, I am confident in providing a targeted set of parameters for fuzzing.
16/2	2026/09/17 15:13	tool	set-results	0m Args: { "EnableConfigs": [ "INET", "IPV6", "SYN_COOKIES", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "sol_tcp_sockopt", "tcp_ecn_create_request", "tcp_syn_options", "tcp_synack_options", "tcp_established_options", "cookie_v4_check", "cookie_v6_check" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options (and BPF sockopt support) allowing per-socket overrides for ECN and AccECN behavior. It alters TCP socket option handling, option formatting in SYN/SYN-ACK/established packets, SYN cookie processing, and connection request creation in reachable core networking code.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "INET", "IPV6", "SYN_COOKIES", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "sol_tcp_sockopt", "tcp_ecn_create_request", "tcp_syn_options", "tcp_synack_options", "tcp_established_options", "cookie_v4_check", "cookie_v6_check" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options (and BPF sockopt support) allowing per-socket overrides for ECN and AccECN behavior. It alters TCP socket option handling, option formatting in SYN/SYN-ACK/established packets, SYN cookie processing, and connection request creation in reachable core networking code.", "WorthFuzzing": true }
17/1	2026/09/17 15:13	action	If	3m Args: { "WorthFuzzing": true } Results: null
18/2	2026/09/17 15:13	agent	kmsan-evaluator	3m Model: core Args: null Results: { "KMSANReasoning": "The patch introduces per-socket configuration for TCP ECN mode (TCP_ECN) and Accurate ECN option sending behavior (TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, adding two u8 fields (ecn_mode and ecn_option) to struct tcp_sock.\n\nAnalysis of uninitialized memory risk:\n1. Field initialization: The new fields `tp-\u003eecn_mode` and `tp-\u003eecn_option` are explicitly initialized in `tcp_init_sock()` to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. Child sockets cloned during incoming connections via `tcp_create_openreq_child()` inherit these fields from the listening socket via `inet_csk_clone_lock()`.\n2. Getsockopt / copy to userspace: In `do_tcp_getsockopt()`, reading `TCP_ECN` or `TCP_ECN_OPTION` reads the u8 value into a local scalar `int val`, which is fully initialized (zero-extended) before `copy_to_sockptr()`. No uninitialized memory or structure padding is exposed or leaked to userspace or BPF.\n3. Setsockopt / input handling: `do_tcp_setsockopt()` validates integer input bounds and writes valid values to the struct fields.\n4. Surrounding logic: The helper functions `tcp_ecn_mode_eff()` and `tcp_accecn_option_eff()` fallback cleanly to the netns sysctl values if the per-socket option is unspecified. No conditional branches operate on uninitialized variables or memory buffers.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not justified. Standard KASAN fuzzing and compiler warnings/UBSAN are sufficient.", "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 5284afe60b184262a326325db48301b3fe54f95a Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 17 14:59:59 2026 +0000 syz-cluster: applied patch under review diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 208f46967ee59..2e55d9e2eb09a 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -528,6 +528,43 @@ tcp_ecn_fallback - BOOLEAN Default: 1 (enabled) +tcp_ecn (socket option) - TCP_ECN + Per-socket control of ECN mode, allowing per-connection override of the + tcp_ecn sysctl setting. This enables L4S (Low Latency, Low Loss, Scalable + Throughput) configuration on a per-socket basis. + + Setting this socket option to any value except 255 will override the + system-wide tcp_ecn sysctl for that particular socket. A value of 255 + (TCP_ECN_MODE_UNSPEC) means use the system default sysctl value. + + Possible values: 0-5 (see tcp_ecn sysctl description above), or 255 to + use the system default (sysctl_tcp_ecn). + + Example:: + + int val = 3; /* AccECN mode / + setsockopt(fd, SOL_TCP, TCP_ECN, &val, sizeof(val)); + + Default: 255 (unspecified - uses tcp_ecn sysctl value) + +tcp_ecn_option (socket option) - TCP_ECN_OPTION + Per-socket control of Accurate ECN (AccECN) option sending behavior, + allowing per-connection override of the tcp_ecn_option sysctl setting. + + Setting this socket option to any value except 255 will override the + system-wide tcp_ecn_option sysctl for that particular socket. A value of + 255 (TCP_ACCECN_OPTION_UNSPEC) means use the system default sysctl value. + + Possible values: 0-3 (see tcp_ecn_option sysctl description above), or 255 + to use the system default (sysctl_tcp_ecn_option). + + Example:: + + int val = 2; / Send AccECN option on every packet / + setsockopt(fd, SOL_TCP, TCP_ECN_OPTION, &val, sizeof(val)); + + Default: 255 (unspecified - uses tcp_ecn_option sysctl value) + tcp_fack - BOOLEAN This is a legacy option, it has no effect anymore. diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 6a8c77719322f..7cb1e765f4618 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -289,6 +289,13 @@ struct tcp_sock { sacked_out > 0) / u8 ecn_flags; / ECN status bits. / + u8 ecn_mode; / Per-socket ECN mode override + * (TCP_ECN_MODE_UNSPEC = use sysctl) + / + u8 ecn_option; / Per-socket AccECN option override + * (TCP_ACCECN_OPTION_UNSPEC = use sysctl) + / + __cacheline_group_end(tcp_sock_write_tx); / TXRX read-write hotpath cache lines / diff --git a/include/net/tcp.h b/include/net/tcp.h index 5e5f5f9b89a38..b7c0b519ac078 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -707,12 +707,6 @@ u64 cookie_init_timestamp(struct request_sock req, u64 now); bool cookie_timestamp_decode(const struct net net, struct tcp_options_received opt); -static inline bool cookie_ecn_ok(const struct net net, const struct dst_entry dst) -{ - return READ_ONCE(net->ipv4.sysctl_tcp_ecn) \|\| - dst_feature(dst, RTAX_FEATURE_ECN); -} - #if IS_ENABLED(CONFIG_BPF) static inline bool cookie_bpf_ok(struct sk_buff skb) { diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index 865d5c5a7718d..48e364c458b29 100644 --- a/include/net/tcp_ecn.h +++ b/include/net/tcp_ecn.h @@ -22,6 +22,7 @@ enum tcp_ecn_mode { TCP_ECN_IN_ACCECN_OUT_ACCECN = 3, TCP_ECN_IN_ACCECN_OUT_ECN = 4, TCP_ECN_IN_ACCECN_OUT_NOECN = 5, + TCP_ECN_MODE_UNSPEC = 255, / Use sysctl default (per-socket) / }; / AccECN option sending when AccECN has been successfully negotiated / @@ -30,8 +31,36 @@ enum tcp_accecn_option { TCP_ACCECN_OPTION_MINIMUM = 1, TCP_ACCECN_OPTION_FULL = 2, TCP_ACCECN_OPTION_PERSIST = 3, + TCP_ACCECN_OPTION_UNSPEC = 255, / Use sysctl default (per-socket) / }; +/ Resolve the effective ECN mode: per-socket override or sysctl fallback / +static inline u8 tcp_ecn_mode_eff(const struct sock sk) +{ + u8 mode = READ_ONCE(tcp_sk(sk)->ecn_mode); + + if (mode == TCP_ECN_MODE_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn); + return mode; +} + +/* Resolve the effective AccECN option: per-socket override or sysctl fallback / +static inline u8 tcp_accecn_option_eff(const struct sock sk) +{ + u8 opt = READ_ONCE(tcp_sk(sk)->ecn_option); + + if (opt == TCP_ACCECN_OPTION_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + return opt; +} + +/* ECN support for SYN cookies: per-socket override or route feature / +static inline bool cookie_ecn_ok(const struct sock sk, const struct dst_entry dst) +{ + return tcp_ecn_mode_eff(sk) \|\| + dst_feature(dst, RTAX_FEATURE_ECN); +} + / Apply either ECT(0) or ECT(1) based on TCP_CONG_ECT_1_NEGOTIATION flag / static inline void INET_ECN_xmit_ect_1_negotiation(struct sock sk) { @@ -599,7 +628,7 @@ static inline void tcp_ecn_send_syn(struct sock sk, struct sk_buff skb) struct tcp_sock tp = tcp_sk(sk); bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk); bool use_ecn, use_accecn; - u8 tcp_ecn = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn); + u8 tcp_ecn = tcp_ecn_mode_eff(sk); use_accecn = tcp_ecn == TCP_ECN_IN_ACCECN_OUT_ACCECN \|\| tcp_ca_needs_accecn(sk); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 732b35cc08d1c..c58b1633bb46e 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2985,7 +2985,8 @@ union bpf_attr { TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT, * TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP, * TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX, - * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS. + * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS, + * TCP_ECN, TCP_ECN_OPTION. * * IPPROTO_IP, which supports optname IP_TOS. * * IPPROTO_IPV6, which supports the following optname\ s: * IPV6_TCLASS, IPV6_AUTOFLOWLABEL. diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index 03772dd4d3992..01ebb348ba274 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -142,6 +142,8 @@ enum { #define TCP_RTO_MAX_MS 44 /* max rto time in ms / #define TCP_RTO_MIN_US 45 / min rto time in us / #define TCP_DELACK_MAX_US 46 / max delayed ack time in us / +#define TCP_ECN 47 / Per-socket ECN mode (0-5, 255=use sysctl) / +#define TCP_ECN_OPTION 48 / Per-socket AccECN option (0-3, 255=use sysctl) / #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/net/core/filter.c b/net/core/filter.c index 61940e7535523..993b31e10b944 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5670,6 +5670,8 @@ static int sol_tcp_sockopt(struct sock sk, int optname, case TCP_NOTSENT_LOWAT: case TCP_SAVE_SYN: case TCP_RTO_MAX_MS: + case TCP_ECN: + case TCP_ECN_OPTION: if (optlen != sizeof(int)) return -EINVAL; break; diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 73e1297681847..ebc438bc6a461 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -490,7 +490,7 @@ struct sock cookie_v4_check(struct sock sk, struct sk_buff skb) / if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; - ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst); + ireq->ecn_ok &= cookie_ecn_ok(sk, &rt->dst); treq->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst); diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 1c867a3024446..fb376a97f0e6d 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -463,6 +463,8 @@ void tcp_init_sock(struct sock sk) tp->tsoffset = 0; tp->rack.reo_wnd_steps = 1; + tp->ecn_mode = TCP_ECN_MODE_UNSPEC; + tp->ecn_option = TCP_ACCECN_OPTION_UNSPEC; sk->sk_write_space = sk_stream_write_space; sock_set_flag(sk, SOCK_USE_WRITE_QUEUE); @@ -4160,6 +4162,18 @@ int do_tcp_setsockopt(struct sock sk, int level, int optname, tcp_enable_tx_delay(sk, val); WRITE_ONCE(tp->tcp_tx_delay, val); break; + case TCP_ECN: + if (val != TCP_ECN_MODE_UNSPEC && (val < 0 \|\| val > TCP_ECN_IN_ACCECN_OUT_NOECN)) + err = -EINVAL; + else + WRITE_ONCE(tp->ecn_mode, val); + break; + case TCP_ECN_OPTION: + if (val != TCP_ACCECN_OPTION_UNSPEC && (val < 0 \|\| val > TCP_ACCECN_OPTION_PERSIST)) + err = -EINVAL; + else + WRITE_ONCE(tp->ecn_option, val); + break; default: err = -ENOPROTOOPT; break; @@ -4842,6 +4856,12 @@ int do_tcp_getsockopt(struct sock sk, int level, case TCP_DELACK_MAX_US: val = jiffies_to_usecs(READ_ONCE(inet_csk(sk)->icsk_delack_max)); break; + case TCP_ECN: + val = READ_ONCE(tp->ecn_mode); + break; + case TCP_ECN_OPTION: + val = READ_ONCE(tp->ecn_option); + break; default: return -ENOPROTOOPT; } @@ -5256,6 +5276,8 @@ static void __init tcp_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, tsorted_sent_queue); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, highest_sack); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_flags); + CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_mode); + CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_tx, ecn_option); /* TXRX read-write hotpath cache lines / CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, pred_flags); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 0f60a1dbf9274..0043b4b2bc922 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -7457,13 +7457,12 @@ static void tcp_ecn_create_request(struct request_sock req, const struct dst_entry dst) { const struct tcphdr th = tcp_hdr(skb); - const struct net net = sock_net(listen_sk); bool th_ecn = th->ece && th->cwr; bool ect, ecn_ok; u32 ecn_ok_dst; if (tcp_accecn_syn_requested(th) && - (READ_ONCE(net->ipv4.sysctl_tcp_ecn) >= 3 \|\| + (tcp_ecn_mode_eff(listen_sk) >= 3 \|\| tcp_ca_needs_accecn(listen_sk))) { inet_rsk(req)->ecn_ok = 1; tcp_rsk(req)->accecn_ok = 1; @@ -7477,7 +7476,7 @@ static void tcp_ecn_create_request(struct request_sock req, ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield); ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK); - ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) \|\| ecn_ok_dst; + ecn_ok = tcp_ecn_mode_eff(listen_sk) \|\| ecn_ok_dst; if (((!ect \|\| th->res1 \|\| th->ae) && ecn_ok) \|\| tcp_ca_needs_ecn(listen_sk) \|\| diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 00417a4292225..82b96c4015fd0 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1045,7 +1045,7 @@ static unsigned int tcp_syn_options(struct sock sk, struct sk_buff skb, if (unlikely((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK) && tcp_ecn_mode_accecn(tp) && inet_csk(sk)->icsk_retransmits < 2 && - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) && + tcp_accecn_option_eff(sk) && remaining >= TCPOLEN_ACCECN_BASE)) { opts->use_synack_ecn_bytes = 1; remaining -= tcp_options_fit_accecn(opts, 0, remaining); @@ -1133,7 +1133,7 @@ static unsigned int tcp_synack_options(const struct sock sk, smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining); if (treq->accecn_ok && - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) && + tcp_accecn_option_eff(sk) && synack_type != TCP_SYNACK_RETRANS && remaining >= TCPOLEN_ACCECN_BASE) { opts->use_synack_ecn_bytes = 1; remaining -= tcp_options_fit_accecn(opts, 0, remaining); @@ -1221,7 +1221,7 @@ static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb } if (tcp_ecn_mode_accecn(tp)) { - int ecn_opt = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + int ecn_opt = tcp_accecn_option_eff(sk); if (ecn_opt && tp->saw_accecn_opt && (ecn_opt >= TCP_ACCECN_OPTION_PERSIST \|\| diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c index b581cb1ee2e8a..06efcbf463467 100644 --- a/net/ipv6/syncookies.c +++ b/net/ipv6/syncookies.c @@ -271,7 +271,7 @@ struct sock cookie_v6_check(struct sock sk, struct sk_buff skb) / if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; - ireq->ecn_ok &= cookie_ecn_ok(net, dst); + ireq->ecn_ok &= cookie_ecn_ok(sk, dst); tcp_rsk(req)->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, dst); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 732b35cc08d1c..c58b1633bb46e 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -2985,7 +2985,8 @@ union bpf_attr { TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT, * TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP, * TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX, - * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS. + * TCP_BPF_RTO_MIN, TCP_BPF_SOCK_OPS_CB_FLAGS, + * TCP_ECN, TCP_ECN_OPTION. * * IPPROTO_IP, which supports optname IP_TOS. * * IPPROTO_IPV6, which supports the following optname\ s: * IPV6_TCLASS, IPV6_AUTOFLOWLABEL. diff --git a/tools/include/uapi/linux/tcp.h b/tools/include/uapi/linux/tcp.h index 13ceeb395eb8f..4f52b9df42661 100644 --- a/tools/include/uapi/linux/tcp.h +++ b/tools/include/uapi/linux/tcp.h @@ -128,7 +128,8 @@ enum { #define TCP_CM_INQ TCP_INQ #define TCP_TX_DELAY 37 /* delay outgoing packets by XX usec / - +#define TCP_ECN 47 / Per-socket ECN mode (0-5, 255=use sysctl) / +#define TCP_ECN_OPTION 48 / Per-socket AccECN option (0-3, 255=use sysctl) */ #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h index 593b38f904174..8d6ee2411db86 100644 --- a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h +++ b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h @@ -59,6 +59,8 @@ #define TCP_CA_NAME_MAX 16 #define TCP_NAGLE_OFF 1 #define TCP_RTO_MAX_MS 44 +#define TCP_ECN 47 +#define TCP_ECN_OPTION 48 #define TCP_ECN_OK 1 #define TCP_ECN_QUEUE_CWR 2 diff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c b/tools/testing/selftests/bpf/progs/setget_sockopt.c index d96e99b67aebf..fb97fa0bc7b47 100644 --- a/tools/testing/selftests/bpf/progs/setget_sockopt.c +++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c @@ -64,6 +64,8 @@ static const struct sockopt_test sol_tcp_tests[] = { { .opt = TCP_BPF_DELACK_MAX, .new = 30000, .expected = 30000, }, { .opt = TCP_BPF_RTO_MIN, .new = 30000, .expected = 30000, }, { .opt = TCP_RTO_MAX_MS, .new = 2000, .expected = 2000, }, + { .opt = TCP_ECN, .new = 3, .expected = 3, .restore = 255, }, + { .opt = TCP_ECN_OPTION, .new = 2, .expected = 2, .restore = 255, }, { .opt = 0, }, };
19/3	2026/09/17 15:13	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 8597 output: 30 thoughts: 261 Thoughts: KMSAN Fuzzing Justification: TCP ECN Patch Alright, let's see if this patch warrants a dedicated KMSAN fuzzing run. We're adding `TCP_ECN` and `TCP_ECN_OPTION` socket options for TCP, and we have new fields `tp->ecn_mode` and `tp->ecn_option` in the `struct tcp_sock`. The initialization in `tcp_init_sock()` looks straightforward enough: setting them to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. But wait a minute... what about socket creation and cloning? My immediate concern is, are these new fields being properly handled when a child socket is created or cloned from a parent? Is `tcp_create_openreq_child` copying the `tp` struct, or is `tcp_init_sock` re-initializing them? I need to verify how these socket structures are being allocated and initialized, specifically within functions like `tcp_create_openreq_child` and `sk_clone_lock`. Time to break out `grepper` and see how this data is copied or initialized! This is a classic area where KMSAN can sniff out potential uninitialized memory reads or writes if things aren't handled correctly during socket creation and cloning.
20/3	2026/09/17 15:13	tool	grepper	0m Args: { "Expression": "tcp_init_sock", "PathPrefix": "net/ipv4/" } Results: { "Output": "net/ipv4/af_inet.c=1753=static __net_exit void ipv4_mib_exit_net(struct net net)\n--\nnet/ipv4/af_inet.c-1761-#ifdef CONFIG_MPTCP\nnet/ipv4/af_inet.c:1762:\t/ allocated on demand, see mptcp_init_sock() /\nnet/ipv4/af_inet.c-1763-\tfree_percpu(net-\u003emib.mptcp_statistics);\n--\nnet/ipv4/tcp.c=402=void tcp_md5_destruct_sock(struct sock sk)\n--\nnet/ipv4/tcp.c-419- /\nnet/ipv4/tcp.c:420:void tcp_init_sock(struct sock sk)\nnet/ipv4/tcp.c-421-{\n--\nnet/ipv4/tcp_ipv4.c=2396=static int tcp_v4_init_sock(struct sock *sk)\n--\nnet/ipv4/tcp_ipv4.c-2399-\nnet/ipv4/tcp_ipv4.c:2400:\ttcp_init_sock(sk);\nnet/ipv4/tcp_ipv4.c-2401-\n" }
21/3	2026/09/17 15:13	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9503 output: 33 thoughts: 25 Thoughts: Here's my attempt at summarizing that thought process, tailored for an expert audience: Diving into the Socket Cloning and Connection Establishment Alright, let's get down to brass tacks. I need to refresh my understanding of the kernel's socket handling, specifically how it manages connection cloning and child requests. My brain is turning towards `sk_clone_lock` and `tcp_create_openreq_child`. I'm going to quickly review their interactions. I need to grok how these two work together within the connection lifecycle. Essentially, how are they responsible for the instantiation and management of a new socket that inherits from a listening one. I have a feeling I'll be re-examining the associated locking and synchronization that's involved, especially considering potential race conditions when a child socket is spawned on demand. Time to dive in.
22/3	2026/09/17 15:13	tool	grepper	0m Args: { "Expression": "tcp_create_openreq_child", "PathPrefix": "net/ipv4/" } Results: { "Output": "net/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/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=491=int tcp_v4_err(struct sk_buff skb, u32 info)\n--\nnet/ipv4/tcp_ipv4.c-552-\ttp = tcp_sk(sk);\nnet/ipv4/tcp_ipv4.c:553:\t/ XXX (TFO) - tp-\u003esnd_una should be ISN (tcp_create_openreq_child() /\nnet/ipv4/tcp_ipv4.c-554-\tfastopen = rcu_dereference(tp-\u003efastopen_rsk);\n--\nnet/ipv4/tcp_ipv4.c=1674=struct sock tcp_v4_syn_recv_sock(const struct sock sk, struct sk_buff skb,\n--\nnet/ipv4/tcp_ipv4.c-1696-\nnet/ipv4/tcp_ipv4.c:1697:\tnewsk = tcp_create_openreq_child(sk, req, skb);\nnet/ipv4/tcp_ipv4.c-1698-\tif (!newsk)\n--\nnet/ipv4/tcp_minisocks.c=525=static void smc_check_reset_syn_req(const struct tcp_sock oldtp,\n--\nnet/ipv4/tcp_minisocks.c-545- /\nnet/ipv4/tcp_minisocks.c:546:struct sock tcp_create_openreq_child(const struct sock sk,\nnet/ipv4/tcp_minisocks.c-547-\t\t\t\t struct request_sock *req,\n" }
23/3	2026/09/17 15:13	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 10548 output: 40 thoughts: 29 Thoughts: Okay, let's dive into this. Here's my take on examining that function, presented as a direct thought process: Diving into `tcp_create_openreq_child` Alright, time to get my hands dirty. I want to understand a specific function, `tcp_create_openreq_child`. Specifically, I'm going to find it in the `net/ipv4/tcp_minisocks.c` file. I'm going to look at how the kernel handles the creation of a "child" connection from an established listening socket. I expect this to be core to understanding how TCP connections are established on the receiving end, the handshake process, and potentially how connection tracking is handled within the Linux kernel's TCP implementation. I'm interested in how it handles new incoming connections, resource allocation, and any potential security considerations that might arise during this crucial stage of the connection process. Hopefully, this will shed some light on the deeper workings of the TCP stack. Let's see what we find!
24/3	2026/09/17 15:13	tool	read-file	0m Args: { "File": "net/ipv4/tcp_minisocks.c", "FirstLine": 546, "LineCount": 50 } Results: { "Contents": " 546:\tstruct sock tcp_create_openreq_child(const struct sock sk,\n 547:\t\t\t\t\t struct request_sock req,\n 548:\t\t\t\t\t struct sk_buff skb)\n 549:\t{\n 550:\t\tstruct sock newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);\n 551:\t\tconst struct inet_request_sock ireq = inet_rsk(req);\n 552:\t\tstruct tcp_request_sock treq = tcp_rsk(req);\n 553:\t\tstruct inet_connection_sock newicsk;\n 554:\t\tconst struct tcp_sock oldtp;\n 555:\t\tstruct tcp_sock newtp;\n 556:\t\tu32 seq;\n 557:\t\n 558:\t\tif (!newsk)\n 559:\t\t\treturn NULL;\n 560:\t\n 561:\t\tnewicsk = inet_csk(newsk);\n 562:\t\tnewtp = tcp_sk(newsk);\n 563:\t\toldtp = tcp_sk(sk);\n 564:\t\n 565:\t\tsmc_check_reset_syn_req(oldtp, req, newtp);\n 566:\t\n 567:\t\t/* Now setup tcp_sock */\n 568:\t\tnewtp-\u003epred_flags = 0;\n 569:\t\n 570:\t\tseq = treq-\u003ercv_isn + 1;\n 571:\t\tnewtp-\u003ercv_wup = seq;\n 572:\t\tWRITE_ONCE(newtp-\u003ecopied_seq, seq);\n 573:\t\tWRITE_ONCE(newtp-\u003ercv_nxt, seq);\n 574:\t\tnewtp-\u003esegs_in = 1;\n 575:\t\n 576:\t\tseq = treq-\u003esnt_isn + 1;\n 577:\t\tnewtp-\u003esnd_sml = newtp-\u003esnd_una = seq;\n 578:\t\tWRITE_ONCE(newtp-\u003esnd_nxt, seq);\n 579:\t\tnewtp-\u003esnd_up = seq;\n 580:\t\n 581:\t\tINIT_LIST_HEAD(\u0026newtp-\u003etsq_node);\n 582:\t\tINIT_LIST_HEAD(\u0026newtp-\u003etsorted_sent_queue);\n 583:\t\n 584:\t\ttcp_init_wl(newtp, treq-\u003ercv_isn);\n 585:\t\n 586:\t\tminmax_reset(\u0026newtp-\u003ertt_min, tcp_jiffies32, ~0U);\n 587:\t\tnewicsk-\u003eicsk_ack.lrcvtime = tcp_jiffies32;\n 588:\t\n 589:\t\tnewtp-\u003elsndtime = tcp_jiffies32;\n 590:\t\tnewsk-\u003esk_txhash = READ_ONCE(treq-\u003etxhash);\n 591:\t\tnewtp-\u003etotal_retrans = req-\u003enum_retrans;\n 592:\t\n 593:\t\ttcp_init_xmit_timers(newsk);\n 594:\t\tWRITE_ONCE(newtp-\u003ewrite_seq, newtp-\u003epushed_seq = treq-\u003esnt_isn + 1);\n 595:\t\n" }
25/3	2026/09/17 15:13	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11703 output: 32 thoughts: 101 Thoughts: Inheriting ECN Settings in Socket Cloning Okay, so I'm looking at `inet_csk_clone_lock(sk, req, GFP_ATOMIC)`. It seems like this function eventually calls `sk_clone_lock(sk, priority)`, and that's where the magic happens. A full copy of the `struct sock`, including the embedded `tcp_sock` (and therefore all the TCP-specific data like `ecn_mode` and `ecn_option`), is performed during this cloning process via `sk_prot->obj_size`. That's good news; it implies the ECN settings are automatically inherited from the original socket (`sk`) to the new one! I'm pretty sure that's how it works, but I always believe in double-checking, especially when dealing with core networking components. Just to be completely certain, I'm going to quickly review the implementation of `sk_clone_lock` to confirm that the copy includes the fields I'm interested in. Better safe than sorry.
26/3	2026/09/17 15:13	tool	grepper	0m Args: { "Expression": "sk_clone_lock", "PathPrefix": "net/core/sock.c" } Results: { "Output": "net/core/sock.c=2209=static void sock_copy(struct sock nsk, const struct sock osk)\n--\nnet/core/sock.c-2217-\t * we must check if sk_tx_queue_clear() is called after\nnet/core/sock.c:2218:\t * sock_copy() in sk_clone_lock().\nnet/core/sock.c-2219-\t */\n" }
27/3	2026/09/17 15:13	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 12176 output: 37 thoughts: 153 Thoughts: My Analysis of `sk_clone_lock` and `do_tcp_getsockopt` in Relation to TCP ECN Okay, so if I understand this correctly, `sk_clone_lock` essentially duplicates the entire object using `sock_copy`, meaning it copies a chunk of data equal to `sk_prot->obj_size`. That's the setup. Now, I'm interested in how TCP ECN settings are handled, particularly how information flows back to userspace via `getsockopt`. Let's dig into `do_tcp_getsockopt`. From the code snippet you provided, I can see that retrieving the `TCP_ECN` and `TCP_ECN_OPTION` options simply involves reading the values of `tp->ecn_mode` and `tp->ecn_option`, respectively. These are then assigned to `val`. The question is, how does `val` then get communicated back to the application? I need to track `val` after this point. I'll focus my investigation of `tcp.c` around line 4850 and examine the function call stack to figure out how `val` is actually returned to the application.
28/3	2026/09/17 15:14	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4830, "LineCount": 50 } Results: { "Contents": "4830:\t\tcase TCP_AO_REPAIR:\n4831:\t\t\tif (!tcp_can_repair_sock(sk))\n4832:\t\t\t\treturn -EPERM;\n4833:\t\t\treturn tcp_ao_get_repair(sk, optval, optlen);\n4834:\t\tcase TCP_AO_GET_KEYS:\n4835:\t\tcase TCP_AO_INFO: {\n4836:\t\t\tint err;\n4837:\t\n4838:\t\t\tsockopt_lock_sock(sk);\n4839:\t\t\tif (optname == TCP_AO_GET_KEYS)\n4840:\t\t\t\terr = tcp_ao_get_mkts(sk, optval, optlen);\n4841:\t\t\telse\n4842:\t\t\t\terr = tcp_ao_get_sock_info(sk, optval, optlen);\n4843:\t\t\tsockopt_release_sock(sk);\n4844:\t\n4845:\t\t\treturn err;\n4846:\t\t}\n4847:\t\tcase TCP_IS_MPTCP:\n4848:\t\t\tval = 0;\n4849:\t\t\tbreak;\n4850:\t\tcase TCP_RTO_MAX_MS:\n4851:\t\t\tval = jiffies_to_msecs(tcp_rto_max(sk));\n4852:\t\t\tbreak;\n4853:\t\tcase TCP_RTO_MIN_US:\n4854:\t\t\tval = jiffies_to_usecs(READ_ONCE(inet_csk(sk)-\u003eicsk_rto_min));\n4855:\t\t\tbreak;\n4856:\t\tcase TCP_DELACK_MAX_US:\n4857:\t\t\tval = jiffies_to_usecs(READ_ONCE(inet_csk(sk)-\u003eicsk_delack_max));\n4858:\t\t\tbreak;\n4859:\t\tcase TCP_ECN:\n4860:\t\t\tval = READ_ONCE(tp-\u003eecn_mode);\n4861:\t\t\tbreak;\n4862:\t\tcase TCP_ECN_OPTION:\n4863:\t\t\tval = READ_ONCE(tp-\u003eecn_option);\n4864:\t\t\tbreak;\n4865:\t\tdefault:\n4866:\t\t\treturn -ENOPROTOOPT;\n4867:\t\t}\n4868:\t\n4869:\t\tif (copy_to_sockptr(optlen, \u0026len, sizeof(int)))\n4870:\t\t\treturn -EFAULT;\n4871:\t\tif (copy_to_sockptr(optval, \u0026val, len))\n4872:\t\t\treturn -EFAULT;\n4873:\t\treturn 0;\n4874:\t}\n4875:\t\n4876:\tbool tcp_bpf_bypass_getsockopt(int level, int optname)\n4877:\t{\n4878:\t\t/* TCP do_tcp_getsockopt has optimized getsockopt implementation\n4879:\t\t * to avoid extra socket lock for TCP_ZEROCOPY_RECEIVE.\n" }
29/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13412 output: 37 thoughts: 72 Thoughts: Here's my analysis of what's happening, keeping in mind my expertise: Dissecting the `ecn_mode` Assignment Okay, so I'm looking at this bit of code and immediately focusing on `int val;` followed by `val = READ_ONCE(tp->ecn_mode);`. I understand this means we're dealing with a local integer variable, `val`. The important thing here is the use of `READ_ONCE`. This tells me we're reading `tp->ecn_mode`, which likely is a field within a TCP control block or some related data structure, without any concurrency protection. `READ_ONCE` suggests we're expecting this value to be relatively static, or that any temporary inconsistency is acceptable given other considerations (e.g., this value is only used in a limited scope, or it's updated with appropriate synchronization elsewhere). It's crucial to understand the implications of reading without a lock; potential race conditions are the obvious concern. I need to keep in mind the possible side effects. The next step is to examine how `len` (which I see is handled above) and `val` are initialized and used within `do_tcp_getsockopt`. This is the critical next step. I need to understand the context of the `getsockopt` call and determine what's being done with those values, as that will drive any potential concerns about concurrency, data integrity, and potential vulnerabilities. I need to understand what this `ecn_mode` variable controls and how it impacts the TCP stack behavior.
30/3	2026/09/17 15:14	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4600, "LineCount": 40 } Results: { "Contents": "4600:\t\t\tlen = min_t(unsigned int, len, TCP_CA_NAME_MAX);\n4601:\t\t\tif (copy_to_sockptr(optlen, \u0026len, sizeof(int)))\n4602:\t\t\t\treturn -EFAULT;\n4603:\t\n4604:\t\t\trcu_read_lock();\n4605:\t\t\tmemcpy(ca_name, READ_ONCE(icsk-\u003eicsk_ca_ops)-\u003ename,\n4606:\t\t\t sizeof(ca_name));\n4607:\t\t\trcu_read_unlock();\n4608:\t\n4609:\t\t\tif (copy_to_sockptr(optval, ca_name, len))\n4610:\t\t\t\treturn -EFAULT;\n4611:\t\t\treturn 0;\n4612:\t\t}\n4613:\t\tcase TCP_ULP:\n4614:\t\t\tif (copy_from_sockptr(\u0026len, optlen, sizeof(int)))\n4615:\t\t\t\treturn -EFAULT;\n4616:\t\t\tlen = min_t(unsigned int, len, TCP_ULP_NAME_MAX);\n4617:\t\t\tif (!icsk-\u003eicsk_ulp_ops) {\n4618:\t\t\t\tlen = 0;\n4619:\t\t\t\tif (copy_to_sockptr(optlen, \u0026len, sizeof(int)))\n4620:\t\t\t\t\treturn -EFAULT;\n4621:\t\t\t\treturn 0;\n4622:\t\t\t}\n4623:\t\t\tif (copy_to_sockptr(optlen, \u0026len, sizeof(int)))\n4624:\t\t\t\treturn -EFAULT;\n4625:\t\t\tif (copy_to_sockptr(optval, icsk-\u003eicsk_ulp_ops-\u003ename, len))\n4626:\t\t\t\treturn -EFAULT;\n4627:\t\t\treturn 0;\n4628:\t\n4629:\t\tcase TCP_FASTOPEN_KEY: {\n4630:\t\t\tu64 key[TCP_FASTOPEN_KEY_BUF_LENGTH / sizeof(u64)];\n4631:\t\t\tunsigned int key_len;\n4632:\t\n4633:\t\t\tif (copy_from_sockptr(\u0026len, optlen, sizeof(int)))\n4634:\t\t\t\treturn -EFAULT;\n4635:\t\n4636:\t\t\tkey_len = tcp_fastopen_get_cipher(net, icsk, key) *\n4637:\t\t\t\t\tTCP_FASTOPEN_KEY_LENGTH;\n4638:\t\t\tlen = min_t(unsigned int, len, key_len);\n4639:\t\t\tif (copy_to_sockptr(optlen, \u0026len, sizeof(int)))\n" }
31/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 14544 output: 37 thoughts: 16 Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person: Initial Dive into `do_tcp_getsockopt` Alright, so we're starting to look at the beginning of the `do_tcp_getsockopt` function. Immediately, my mind starts sifting through the layers. This is the entry point for retrieving socket options at the TCP level, so we're dealing with the core logic. I'm already anticipating the typical control flow: validation of arguments, dispatch to the appropriate option-specific handler, and then the final retrieval and formatting of the requested information. The kernel-level socket options architecture immediately comes to mind. What are we trying to extract here, and what security checks are already assumed within the system? I'm wondering if there is an explicit lock held. Is it called with the read_lock held? What are the potential pitfalls, race conditions, or performance bottlenecks lurking within this critical path? I need to focus on the structure of the call: what arguments does it expect, and what does it return? I need to start forming a mental model of how it interacts with the underlying TCP state, especially if the current socket is in the midst of a connection or transfer. Okay, let's get into the code and see what we're looking at.
32/3	2026/09/17 15:14	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4520, "LineCount": 40 } Results: { "Contents": "4520:\t\t\t\tval = tp-\u003erx_opt.mss_clamp;\n4521:\t\t\tbreak;\n4522:\t\tcase TCP_NODELAY:\n4523:\t\t\tval = !!(tp-\u003enonagle\u0026TCP_NAGLE_OFF);\n4524:\t\t\tbreak;\n4525:\t\tcase TCP_CORK:\n4526:\t\t\tval = !!(tp-\u003enonagle\u0026TCP_NAGLE_CORK);\n4527:\t\t\tbreak;\n4528:\t\tcase TCP_KEEPIDLE:\n4529:\t\t\tval = keepalive_time_when(tp) / HZ;\n4530:\t\t\tbreak;\n4531:\t\tcase TCP_KEEPINTVL:\n4532:\t\t\tval = keepalive_intvl_when(tp) / HZ;\n4533:\t\t\tbreak;\n4534:\t\tcase TCP_KEEPCNT:\n4535:\t\t\tval = keepalive_probes(tp);\n4536:\t\t\tbreak;\n4537:\t\tcase TCP_SYNCNT:\n4538:\t\t\tval = READ_ONCE(icsk-\u003eicsk_syn_retries) ? :\n4539:\t\t\t\tREAD_ONCE(net-\u003eipv4.sysctl_tcp_syn_retries);\n4540:\t\t\tbreak;\n4541:\t\tcase TCP_LINGER2:\n4542:\t\t\tval = READ_ONCE(tp-\u003elinger2);\n4543:\t\t\tif (val \u003e= 0)\n4544:\t\t\t\tval = (val ? : READ_ONCE(net-\u003eipv4.sysctl_tcp_fin_timeout)) / HZ;\n4545:\t\t\tbreak;\n4546:\t\tcase TCP_DEFER_ACCEPT:\n4547:\t\t\tval = READ_ONCE(icsk-\u003eicsk_accept_queue.rskq_defer_accept);\n4548:\t\t\tval = retrans_to_secs(val, TCP_TIMEOUT_INIT / HZ,\n4549:\t\t\t\t\t TCP_RTO_MAX / HZ);\n4550:\t\t\tbreak;\n4551:\t\tcase TCP_WINDOW_CLAMP:\n4552:\t\t\tval = READ_ONCE(tp-\u003ewindow_clamp);\n4553:\t\t\tbreak;\n4554:\t\tcase TCP_INFO: {\n4555:\t\t\tstruct tcp_info info;\n4556:\t\n4557:\t\t\tif (copy_from_sockptr(\u0026len, optlen, sizeof(int)))\n4558:\t\t\t\treturn -EFAULT;\n4559:\t\n" }
33/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 15537 output: 37 thoughts: 16 Thoughts: Okay, here's my interpretation of that starting thought, rendered as if it's my own thought process: Diving into `do_tcp_getsockopt` Alright, time to get started. Let's dig into this function, `do_tcp_getsockopt`. I need to understand its behavior thoroughly. This is where the core logic of the socket options lies, it's where the rubber meets the road. Hopefully, this starts us on the right path.
34/3	2026/09/17 15:14	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4480, "LineCount": 40 } Results: { "Contents": "4480:\t\t\t READ_ONCE(tp-\u003etimeout_rehash));\n4481:\t\tnla_put_u32(stats, TCP_NLA_BYTES_NOTSENT,\n4482:\t\t\t max_t(int, 0,\n4483:\t\t\t\t READ_ONCE(tp-\u003ewrite_seq) - READ_ONCE(tp-\u003esnd_nxt)));\n4484:\t\tnla_put_u64_64bit(stats, TCP_NLA_EDT, orig_skb-\u003eskb_mstamp_ns,\n4485:\t\t\t\t TCP_NLA_PAD);\n4486:\t\tif (ack_skb)\n4487:\t\t\tnla_put_u8(stats, TCP_NLA_TTL,\n4488:\t\t\t\t tcp_skb_ttl_or_hop_limit(ack_skb));\n4489:\t\n4490:\t\tnla_put_u32(stats, TCP_NLA_REHASH,\n4491:\t\t\t READ_ONCE(tp-\u003eplb_rehash) + READ_ONCE(tp-\u003etimeout_rehash));\n4492:\t\treturn stats;\n4493:\t}\n4494:\t\n4495:\tint do_tcp_getsockopt(struct sock sk, int level,\n4496:\t\t\t int optname, sockptr_t optval, sockptr_t optlen)\n4497:\t{\n4498:\t\tstruct inet_connection_sock icsk = inet_csk(sk);\n4499:\t\tstruct tcp_sock tp = tcp_sk(sk);\n4500:\t\tstruct net net = sock_net(sk);\n4501:\t\tint user_mss;\n4502:\t\tint val, len;\n4503:\t\n4504:\t\tif (copy_from_sockptr(\u0026len, optlen, sizeof(int)))\n4505:\t\t\treturn -EFAULT;\n4506:\t\n4507:\t\tif (len \u003c 0)\n4508:\t\t\treturn -EINVAL;\n4509:\t\n4510:\t\tlen = min_t(unsigned int, len, sizeof(int));\n4511:\t\n4512:\t\tswitch (optname) {\n4513:\t\tcase TCP_MAXSEG:\n4514:\t\t\tval = tp-\u003emss_cache;\n4515:\t\t\tuser_mss = READ_ONCE(tp-\u003erx_opt.user_mss);\n4516:\t\t\tif (user_mss \u0026\u0026\n4517:\t\t\t ((1 \u003c\u003c sk-\u003esk_state) \u0026 (TCPF_CLOSE \| TCPF_LISTEN)))\n4518:\t\t\t\tval = user_mss;\n4519:\t\t\tif (tp-\u003erepair)\n" }
35/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 16409 output: 30 thoughts: 210 Thoughts: Examining TCP ECN Option Handling Okay, so I'm digging into the `do_tcp_getsockopt` function and how it handles the `TCP_ECN` option. The code says `val` is an `int`. When `optname` is `TCP_ECN`, the value of `val` is set to `READ_ONCE(tp->ecn_mode)`. Aha, `tp->ecn_mode` is promoted from a `u8` to an `int` here. Then, `copy_to_sockptr` copies all 4 bytes of `val` to the user space buffer. The critical thing is that all those bytes of `val` are properly initialized. Now, I need to confirm that `tp->ecn_mode` is set correctly. The code shows that `tcp_init_sock` initializes `tp->ecn_mode` to `TCP_ECN_MODE_UNSPEC`. It also initializes `tp->ecn_option` to `TCP_ACCECN_OPTION_UNSPEC`. But, wait a second... does `tcp_init_sock` get called for every TCP socket? I need to verify that and make sure it's consistent. To be thorough, I'm going to track down all the callers of `tcp_init_sock`, as well as places where a `tcp_sock` structure is created, just to make absolutely sure. And, I really need to check how IPv6 is handled, too, via `tcp_v6_init_sock`, to confirm there's no subtle difference in initialization or behavior.
36/3	2026/09/17 15:14	tool	grepper	0m Args: { "Expression": "tcp_v6_init_sock", "PathPrefix": "net/" } Results: { "Output": "net/ipv6/tcp_ipv6.c=2065=static void tcp6_destruct_sock(struct sock sk)\n--\nnet/ipv6/tcp_ipv6.c-2075- /\nnet/ipv6/tcp_ipv6.c:2076:static int tcp_v6_init_sock(struct sock *sk)\nnet/ipv6/tcp_ipv6.c-2077-{\n--\nnet/ipv6/tcp_ipv6.c=2276=struct proto tcpv6_prot = {\n--\nnet/ipv6/tcp_ipv6.c-2284-\t.ioctl\t\t\t= tcp_ioctl,\nnet/ipv6/tcp_ipv6.c:2285:\t.init\t\t\t= tcp_v6_init_sock,\nnet/ipv6/tcp_ipv6.c-2286-\t.destroy\t\t= tcp_v4_destroy_sock,\n" }
37/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17239 output: 40 thoughts: 17 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `tcp_v6_init_sock` Okay, let's take a look at what the `tcp_v6_init_sock` function is doing. I need to understand how IPv6 TCP sockets are initialized within the kernel. I'm assuming this is a crucial entry point for setting up the basic data structures and states for a new TCPv6 connection. Probably responsible for handling the IPv6-specific socket options and maybe even setting up the initial congestion control parameters depending on the kernel version. I suspect it might call into common TCP socket initialization routines, but I'm curious to see how it handles the IPv6 extensions, especially the address family and scope. I'm also anticipating it’ll manage the flow label if that's relevant to the design of this kernel's IPv6 implementation. Gotta check how it interacts with the underlying networking stack regarding address assignment, route selection, and any potential security checks related to IPv6. I'm looking for the nitty-gritty details, especially about memory allocation and initial state assignment.
38/3	2026/09/17 15:14	tool	read-file	0m Args: { "File": "net/ipv6/tcp_ipv6.c", "FirstLine": 2075, "LineCount": 15 } Results: { "Contents": "2075:\t /\n2076:\tstatic int tcp_v6_init_sock(struct sock sk)\n2077:\t{\n2078:\t\tstruct inet_connection_sock *icsk = inet_csk(sk);\n2079:\t\n2080:\t\ttcp_init_sock(sk);\n2081:\t\n2082:\t\ticsk-\u003eicsk_af_ops = \u0026ipv6_specific;\n2083:\t\n2084:\t#if defined(CONFIG_TCP_MD5SIG) \|\| defined(CONFIG_TCP_AO)\n2085:\t\ttcp_sk(sk)-\u003eaf_specific = \u0026tcp_sock_ipv6_specific;\n2086:\t\tsk-\u003esk_destruct = tcp6_destruct_sock;\n2087:\t#endif\n2088:\t\n2089:\t\treturn 0;\n" }
39/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17776 output: 31 thoughts: 46 Thoughts: Okay, here's my interpretation of this thought process, framed in the first person, as if these were my internal considerations: Initial TCPv6 Socket Initialization - Where's MPTCP? Alright, I'm looking at `tcp_v6_init_sock`, and it's calling `tcp_init_sock(sk)`. Standard TCP setup, got it. But hold on, I immediately start to think about MPTCP, and subflows in particular. I need to be sure the MPTCP layer is properly initialized, and I can't just assume everything is handled. So my immediate next step here is to verify whether `mptcp_init_sock` is being called, or whether it somehow integrated as part of TCP initialisation. Are there any hooks or checks for MPTCP specific initialization within `tcp_init_sock`? I have to consider how MPTCP subflows are managed in relation to this initial socket setup. The documentation should clarify how MPTCP interacts with standard TCP initialization. I'll need to go back and check if it's integrated, or if there's a separate call.
40/3	2026/09/17 15:14	tool	grepper	0m Args: { "Expression": "tcp_init_sock", "PathPrefix": "net/mptcp/" } Results: { "Output": "net/mptcp/protocol.c=3118=static void mptcp_worker(struct work_struct work)\n--\nnet/mptcp/protocol.c-3166-\nnet/mptcp/protocol.c:3167:static void __mptcp_init_sock(struct sock sk)\nnet/mptcp/protocol.c-3168-{\n--\nnet/mptcp/protocol.c-3180-\nnet/mptcp/protocol.c:3181:\t/* msk does not go through tcp_init_sock(); seed RTO bounds. /\nnet/mptcp/protocol.c-3182-\ticsk-\u003eicsk_rto_min =\n--\nnet/mptcp/protocol.c=3210=static void mptcp_ca_reset(struct sock sk)\n--\nnet/mptcp/protocol.c-3222-\nnet/mptcp/protocol.c:3223:static int mptcp_init_sock(struct sock sk)\nnet/mptcp/protocol.c-3224-{\n--\nnet/mptcp/protocol.c-3227-\nnet/mptcp/protocol.c:3228:\t__mptcp_init_sock(sk);\nnet/mptcp/protocol.c-3229-\n--\nnet/mptcp/protocol.c-3244-\nnet/mptcp/protocol.c:3245:\t/ fetch the ca name; do it outside __mptcp_init_sock(), so that clone will\nnet/mptcp/protocol.c-3246-\t * propagate the correct value\n--\nnet/mptcp/protocol.c=3695=struct sock mptcp_sk_clone_init(const struct sock sk,\n--\nnet/mptcp/protocol.c-3712-\nnet/mptcp/protocol.c:3713:\t__mptcp_init_sock(nsk);\nnet/mptcp/protocol.c-3714-\n--\nnet/mptcp/protocol.c=4210=static struct proto mptcp_prot = {\n--\nnet/mptcp/protocol.c-4212-\t.owner\t\t= THIS_MODULE,\nnet/mptcp/protocol.c:4213:\t.init\t\t= mptcp_init_sock,\nnet/mptcp/protocol.c-4214-\t.connect\t= mptcp_connect,\n" }
41/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18740 output: 30 thoughts: 40 Thoughts: MPTCP and ECN: A Quick Check Okay, so I'm just quickly trying to recall something about MPTCP and Explicit Congestion Notification. Did MPTCP handle the standard `TCP_ECN` socket option, or was it a more specific MPTCP-related option, maybe something like `TCP_ECN_OPTION`? Need to clarify that before I move on. I should know this, but better to be safe than sorry and to not waste time. Time to jump into the code. Let me just glance at `net/mptcp/sockopt.c`... that should have the answer.
42/3	2026/09/17 15:14	tool	grepper	0m Error: no matches Args: { "Expression": "TCP_ECN", "PathPrefix": "net/mptcp/" } Results: { "error": "no matches" }
43/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18960 output: 33 thoughts: 58 Thoughts: Okay, here's my interpretation of those thoughts, presented as my own mental process, given my expertise: Checking MPTCP's TCP_ECN Support Alright, so the MPTCP implementation isn't directly handling `TCP_ECN` or the `TCP_ECN_OPTION` socket options, or perhaps it's doing something clever by falling back to the standard TCP functionality. Let me confirm that by delving into the `net/mptcp/sockopt.c` file within the kernel source. I need to understand exactly how the `getsockopt` and `setsockopt` functions are implemented for `SOL_TCP`. That's where the relevant code would be for handling these TCP-level options within the MPTCP context. It's likely that a check for supported options happens, or a passthrough mechanism, or something more complex. My goal is to understand how MPTCP interacts with standard TCP's ECN features, if at all.
44/3	2026/09/17 15:14	tool	grepper	0m Args: { "Expression": "mptcp_getsockopt", "PathPrefix": "net/mptcp/" } Results: { "Output": "net/mptcp/protocol.c=4210=static struct proto mptcp_prot = {\n--\nnet/mptcp/protocol.c-4217-\t.setsockopt\t= mptcp_setsockopt,\nnet/mptcp/protocol.c:4218:\t.getsockopt\t= mptcp_getsockopt,\nnet/mptcp/protocol.c-4219-\t.shutdown\t= mptcp_shutdown,\n--\nnet/mptcp/protocol.h=969=int mptcp_setsockopt(struct sock sk, int level, int optname,\nnet/mptcp/protocol.h-970-\t\t sockptr_t optval, unsigned int optlen);\nnet/mptcp/protocol.h:971:int mptcp_getsockopt(struct sock sk, int level, int optname,\nnet/mptcp/protocol.h-972-\t\t char __user optval, int __user option);\n--\nnet/mptcp/sockopt.c=907=int mptcp_setsockopt(struct sock sk, int level, int optname,\n--\nnet/mptcp/sockopt.c-944-\nnet/mptcp/sockopt.c:945:static int mptcp_getsockopt_first_sf_only(struct mptcp_sock msk, int level, int optname,\nnet/mptcp/sockopt.c-946-\t\t\t\t\t char __user optval, int __user optlen)\n--\nnet/mptcp/sockopt.c=1032=EXPORT_SYMBOL_GPL(mptcp_diag_fill_info);\nnet/mptcp/sockopt.c-1033-\nnet/mptcp/sockopt.c:1034:static int mptcp_getsockopt_info(struct mptcp_sock msk, char __user optval, int __user optlen)\nnet/mptcp/sockopt.c-1035-{\n--\nnet/mptcp/sockopt.c=1080=static int mptcp_get_subflow_data(struct mptcp_subflow_data sfd,\n--\nnet/mptcp/sockopt.c-1117-\nnet/mptcp/sockopt.c:1118:static int mptcp_getsockopt_tcpinfo(struct mptcp_sock msk, char __user optval,\nnet/mptcp/sockopt.c-1119-\t\t\t\t int __user optlen)\n--\nnet/mptcp/sockopt.c=1171=static void mptcp_get_sub_addrs(const struct sock sk, struct mptcp_subflow_addrs a)\n--\nnet/mptcp/sockopt.c-1209-\nnet/mptcp/sockopt.c:1210:static int mptcp_getsockopt_subflow_addrs(struct mptcp_sock msk, char __user optval,\nnet/mptcp/sockopt.c-1211-\t\t\t\t\t int __user optlen)\n--\nnet/mptcp/sockopt.c=1294=static int mptcp_put_full_info(struct mptcp_full_info mfi,\n--\nnet/mptcp/sockopt.c-1307-\nnet/mptcp/sockopt.c:1308:static int mptcp_getsockopt_full_info(struct mptcp_sock msk, char __user optval,\nnet/mptcp/sockopt.c-1309-\t\t\t\t int __user optlen)\n--\nnet/mptcp/sockopt.c=1382=static int mptcp_put_int_option(struct mptcp_sock msk, char __user optval,\n--\nnet/mptcp/sockopt.c-1410-\nnet/mptcp/sockopt.c:1411:static int mptcp_getsockopt_sol_tcp(struct mptcp_sock msk, int optname,\nnet/mptcp/sockopt.c-1412-\t\t\t\t char __user optval, int __user optlen)\n--\nnet/mptcp/sockopt.c-1425-\tcase TCP_FASTOPEN_NO_COOKIE:\nnet/mptcp/sockopt.c:1426:\t\treturn mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,\nnet/mptcp/sockopt.c-1427-\t\t\t\t\t\t optval, optlen);\n--\nnet/mptcp/sockopt.c-1450-\tcase TCP_MAXSEG:\nnet/mptcp/sockopt.c:1451:\t\treturn mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,\nnet/mptcp/sockopt.c-1452-\t\t\t\t\t\t optval, optlen);\n--\nnet/mptcp/sockopt.c-1456-\nnet/mptcp/sockopt.c:1457:static int mptcp_getsockopt_v4(struct mptcp_sock msk, int optname,\nnet/mptcp/sockopt.c-1458-\t\t\t char __user optval, int __user optlen)\n--\nnet/mptcp/sockopt.c-1481-\nnet/mptcp/sockopt.c:1482:static int mptcp_getsockopt_v6(struct mptcp_sock msk, int optname,\nnet/mptcp/sockopt.c-1483-\t\t\t char __user optval, int __user optlen)\n--\nnet/mptcp/sockopt.c-1501-\nnet/mptcp/sockopt.c:1502:static int mptcp_getsockopt_sol_mptcp(struct mptcp_sock msk, int optname,\nnet/mptcp/sockopt.c-1503-\t\t\t\t char __user optval, int __user optlen)\n--\nnet/mptcp/sockopt.c-1506-\tcase MPTCP_INFO:\nnet/mptcp/sockopt.c:1507:\t\treturn mptcp_getsockopt_info(msk, optval, optlen);\nnet/mptcp/sockopt.c-1508-\tcase MPTCP_FULL_INFO:\nnet/mptcp/sockopt.c:1509:\t\treturn mptcp_getsockopt_full_info(msk, optval, optlen);\nnet/mptcp/sockopt.c-1510-\tcase MPTCP_TCPINFO:\nnet/mptcp/sockopt.c:1511:\t\treturn mptcp_getsockopt_tcpinfo(msk, optval, optlen);\nnet/mptcp/sockopt.c-1512-\tcase MPTCP_SUBFLOW_ADDRS:\nnet/mptcp/sockopt.c:1513:\t\treturn mptcp_getsockopt_subflow_addrs(msk, optval, optlen);\nnet/mptcp/sockopt.c-1514-\t}\n--\nnet/mptcp/sockopt.c-1518-\nnet/mptcp/sockopt.c:1519:int mptcp_getsockopt(struct sock sk, int level, int optname,\nnet/mptcp/sockopt.c-1520-\t\t char __user optval, int __user *option)\n--\nnet/mptcp/sockopt.c-1539-\tif (level == SOL_IP)\nnet/mptcp/sockopt.c:1540:\t\treturn mptcp_getsockopt_v4(msk, optname, optval, option);\nnet/mptcp/sockopt.c-1541-\tif (level == SOL_IPV6)\nnet/mptcp/sockopt.c:1542:\t\treturn mptcp_getsockopt_v6(msk, optname, optval, option);\nnet/mptcp/sockopt.c-1543-\tif (level == SOL_TCP)\nnet/mptcp/sockopt.c:1544:\t\treturn mptcp_getsockopt_sol_tcp(msk, optname, optval, option);\nnet/mptcp/sockopt.c-1545-\tif (level == SOL_MPTCP)\nnet/mptcp/sockopt.c:1546:\t\treturn mptcp_getsockopt_sol_mptcp(msk, optname, optval, option);\nnet/mptcp/sockopt.c-1547-\treturn -EOPNOTSUPP;\n" }
45/3	2026/09/17 15:14	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 21488 output: 36 thoughts: 218 Thoughts: Investigating TCP_ECN Support in MPTCP and BPF Sockops Okay, so I'm digging into why `mptcp_getsockopt_sol_tcp` is returning `-EOPNOTSUPP` for `TCP_ECN`. It's clear that it isn't handled directly there. My next thought is, "What about BPF sockops? Maybe they're intercepting it." So I'm now checking `net/core/filter.c` to see how sockopts, and specifically `TCP_ECN`, are handled there. Aha! Looking at `net/core/filter.c`, right around line 5670, I can see that `TCP_ECN` is explicitly included in a `case` statement within `sol_tcp_sockopt`. Specifically it's in a block that seems to handle some basic validation of the option length. Now, I need to understand the wider context. I need to see how `TCP_ECN` is processed in relation to the other options here, and how this relates to BPF sockops. This seems like it could be the key to understanding the issue.
46/3	2026/09/17 15:15	tool	read-file	0m Args: { "File": "net/core/filter.c", "FirstLine": 5660, "LineCount": 40 } Results: { "Contents": "5660:\t\tswitch (optname) {\n5661:\t\tcase TCP_NODELAY:\n5662:\t\tcase TCP_MAXSEG:\n5663:\t\tcase TCP_KEEPIDLE:\n5664:\t\tcase TCP_KEEPINTVL:\n5665:\t\tcase TCP_KEEPCNT:\n5666:\t\tcase TCP_SYNCNT:\n5667:\t\tcase TCP_WINDOW_CLAMP:\n5668:\t\tcase TCP_THIN_LINEAR_TIMEOUTS:\n5669:\t\tcase TCP_USER_TIMEOUT:\n5670:\t\tcase TCP_NOTSENT_LOWAT:\n5671:\t\tcase TCP_SAVE_SYN:\n5672:\t\tcase TCP_RTO_MAX_MS:\n5673:\t\tcase TCP_ECN:\n5674:\t\tcase TCP_ECN_OPTION:\n5675:\t\t\tif (optlen != sizeof(int))\n5676:\t\t\t\treturn -EINVAL;\n5677:\t\t\tbreak;\n5678:\t\tcase TCP_CONGESTION:\n5679:\t\t\treturn sol_tcp_sockopt_congestion(sk, optval, optlen, getopt);\n5680:\t\tcase TCP_SAVED_SYN:\n5681:\t\t\tif (optlen \u003c 1)\n5682:\t\t\t\treturn -EINVAL;\n5683:\t\t\tbreak;\n5684:\t\tdefault:\n5685:\t\t\tif (getopt)\n5686:\t\t\t\treturn bpf_sol_tcp_getsockopt(sk, optname, optval, optlen);\n5687:\t\t\treturn bpf_sol_tcp_setsockopt(sk, optname, optval, optlen);\n5688:\t\t}\n5689:\t\n5690:\t\tif (getopt) {\n5691:\t\t\tif (optname == TCP_SAVED_SYN) {\n5692:\t\t\t\tstruct tcp_sock tp = tcp_sk(sk);\n5693:\t\n5694:\t\t\t\tif (!tp-\u003esaved_syn \|\|\n5695:\t\t\t\t optlen \u003e tcp_saved_syn_len(tp-\u003esaved_syn))\n5696:\t\t\t\t\treturn -EINVAL;\n5697:\t\t\t\tmemcpy(optval, tp-\u003esaved_syn-\u003edata, optlen);\n5698:\t\t\t\t/ It cannot free tp-\u003esaved_syn here because it\n5699:\t\t\t\t * does not know if the user space still needs it.\n" }
47/3	2026/09/17 15:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22628 output: 36 thoughts: 25 Thoughts: Here's a summary of my thought process, as if I were analyzing that code: Diving Back into `sol_tcp_sockopt` in `net/core/filter.c` Alright, I'm heading back into `net/core/filter.c`, specifically focusing on `sol_tcp_sockopt`. I need to get a better handle on the complete implementation. I'm already quite familiar with the overall networking architecture, but a specific function like this can reveal some subtle but critical details about how TCP socket options are handled within the filter mechanism. I want to see how these options are interpreted, validated, and applied (or rejected). Are there any edge cases I should be aware of, perhaps any security implications? Are there potential performance bottlenecks related to this code that I might need to address or document for further study? Understanding this function fully will allow me to have a complete and detailed picture of this area of the networking code.
48/3	2026/09/17 15:15	tool	read-file	0m Args: { "File": "net/core/filter.c", "FirstLine": 5700, "LineCount": 40 } Results: { "Contents": "5700:\t\t\t\t /\n5701:\t\t\t\treturn 0;\n5702:\t\t\t}\n5703:\t\n5704:\t\t\treturn do_tcp_getsockopt(sk, SOL_TCP, optname,\n5705:\t\t\t\t\t\t KERNEL_SOCKPTR(optval),\n5706:\t\t\t\t\t\t KERNEL_SOCKPTR(optlen));\n5707:\t\t}\n5708:\t\n5709:\t\treturn do_tcp_setsockopt(sk, SOL_TCP, optname,\n5710:\t\t\t\t\t KERNEL_SOCKPTR(optval), optlen);\n5711:\t}\n5712:\t\n5713:\tstatic bool sk_allows_sol_ip_sockopt(struct sock sk)\n5714:\t{\n5715:\t\tswitch (sk-\u003esk_family) {\n5716:\t\tcase AF_INET:\n5717:\t\t\treturn true;\n5718:\t\tcase AF_INET6:\n5719:\t\t\t/ Allow getting/setting sockopt for possible ipv4-mapped ipv6 socket. /\n5720:\t\t\treturn sk-\u003esk_type != SOCK_RAW \u0026\u0026 !ipv6_only_sock(sk);\n5721:\t\tdefault:\n5722:\t\t\treturn false;\n5723:\t\t}\n5724:\t}\n5725:\t\n5726:\tstatic int sol_ip_sockopt(struct sock sk, int optname,\n5727:\t\t\t\t char optval, int optlen,\n5728:\t\t\t\t bool getopt)\n5729:\t{\n5730:\t\tif (!sk_allows_sol_ip_sockopt(sk))\n5731:\t\t\treturn -EINVAL;\n5732:\t\n5733:\t\tswitch (optname) {\n5734:\t\tcase IP_TOS:\n5735:\t\tcase IP_TRANSPARENT:\n5736:\t\t\tif (*optlen != sizeof(int))\n5737:\t\t\t\treturn -EINVAL;\n5738:\t\t\tbreak;\n5739:\t\tdefault:\n" }
49/3	2026/09/17 15:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 23439 output: 37 thoughts: 277 Thoughts: Analyzing TCP ECN Sockopts in BPF Okay, so I'm looking at this `sol_tcp_sockopt` BPF code. The crucial thing here is that, as expected, `optlen` has* to be `sizeof(int)`. This makes sense, given what I know about socket options. We then jump into `do_tcp_getsockopt`, which writes a 4-byte integer and returns 0 – standard procedure. Now, let's switch gears and examine `do_tcp_setsockopt`. I'm focusing specifically on the `TCP_ECN` and `TCP_ECN_OPTION` cases. The code snippets for both are straightforward. They're basically sanity checks on the value being set. If `val` is out of the defined range, it returns `-EINVAL`; otherwise, it writes the value. But the key question, as always, is where does this `val` come from? I need to trace back through the code to figure out how `do_tcp_setsockopt` receives its input. I'll need to check `net/ipv4/tcp.c`, specifically around lines 3800 to 3850, to understand how that `val` is being populated. This is where the magic happens, so to speak. Understanding the value's origin is critical to grasp potential security implications and control flows.
50/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 3800, "LineCount": 40 } Results: { "Contents": "3800:\t\t\treturn 0;\n3801:\t\t}\n3802:\t\n3803:\t\told_window_clamp = tp-\u003ewindow_clamp;\n3804:\t\tnew_window_clamp = max_t(int, SOCK_MIN_RCVBUF / 2, val);\n3805:\t\n3806:\t\tif (new_window_clamp == old_window_clamp)\n3807:\t\t\treturn 0;\n3808:\t\n3809:\t\tWRITE_ONCE(tp-\u003ewindow_clamp, new_window_clamp);\n3810:\t\n3811:\t\t/* Need to apply the reserved mem provisioning only\n3812:\t\t * when shrinking the window clamp.\n3813:\t\t /\n3814:\t\tif (new_window_clamp \u003c old_window_clamp) {\n3815:\t\t\t__tcp_adjust_rcv_ssthresh(sk, new_window_clamp);\n3816:\t\t} else {\n3817:\t\t\tnew_rcv_ssthresh = min(tp-\u003ercv_wnd, new_window_clamp);\n3818:\t\t\ttp-\u003ercv_ssthresh = max(new_rcv_ssthresh, tp-\u003ercv_ssthresh);\n3819:\t\t}\n3820:\t\treturn 0;\n3821:\t}\n3822:\t\n3823:\tint tcp_sock_set_maxseg(struct sock sk, int val)\n3824:\t{\n3825:\t\t/* Values greater than interface MTU won't take effect. However\n3826:\t\t * at the point when this call is done we typically don't yet\n3827:\t\t * know which interface is going to be used\n3828:\t\t /\n3829:\t\tif (val \u0026\u0026 (val \u003c TCP_MIN_MSS \|\| val \u003e MAX_TCP_WINDOW))\n3830:\t\t\treturn -EINVAL;\n3831:\t\n3832:\t\tWRITE_ONCE(tcp_sk(sk)-\u003erx_opt.user_mss, val);\n3833:\t\treturn 0;\n3834:\t}\n3835:\t\n3836:\t/\n3837:\t \tSocket option code for TCP.\n3838:\t /\n3839:\tint do_tcp_setsockopt(struct sock *sk, int level, int optname,\n" }
51/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24683 output: 37 thoughts: 16 Thoughts: Okay, here's my interpretation of that starting point, rendered as a first-person summary, keeping in mind my expertise: Diving into `do_tcp_setsockopt` Alright, let's get into the nitty-gritty. "Let's see the start of `do_tcp_setsockopt`". Right, I want to see how this function is architected and what the initial design choices are. It's the entry point, the first place to understand how the system-level socket options are handled for TCP connections. I’m thinking about the layers involved, the interplay with the generic socket layer, and the specific TCP-level configurations this function likely touches. I'll be looking for things like argument validation, error handling, and the basic dispatch mechanism – how it determines which specific socket option is being configured. This function is likely where the rubber meets the road between user-space requests (like those from `setsockopt`) and the kernel's TCP internals. I want to see what assumptions it makes, if any, about the underlying network stack. I'm especially keen to see how it might interact with other TCP state machines, like SYN state management.
52/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 3840, "LineCount": 40 } Results: { "Contents": "3840:\t\t\t sockptr_t optval, unsigned int optlen)\n3841:\t{\n3842:\t\tstruct tcp_sock tp = tcp_sk(sk);\n3843:\t\tstruct inet_connection_sock icsk = inet_csk(sk);\n3844:\t\tstruct net net = sock_net(sk);\n3845:\t\tint val;\n3846:\t\tint err = 0;\n3847:\t\n3848:\t\t/ These are data/string values, all the others are ints */\n3849:\t\tswitch (optname) {\n3850:\t\tcase TCP_CONGESTION: {\n3851:\t\t\tchar name[TCP_CA_NAME_MAX];\n3852:\t\n3853:\t\t\tif (optlen \u003c 1)\n3854:\t\t\t\treturn -EINVAL;\n3855:\t\n3856:\t\t\tval = strncpy_from_sockptr(name, optval,\n3857:\t\t\t\t\t\tmin_t(long, TCP_CA_NAME_MAX-1, optlen));\n3858:\t\t\tif (val \u003c 0)\n3859:\t\t\t\treturn -EFAULT;\n3860:\t\t\tname[val] = 0;\n3861:\t\n3862:\t\t\tsockopt_lock_sock(sk);\n3863:\t\t\terr = tcp_set_congestion_control(sk, name, !has_current_bpf_ctx(),\n3864:\t\t\t\t\t\t\t sockopt_ns_capable(sock_net(sk)-\u003euser_ns,\n3865:\t\t\t\t\t\t\t\t\t CAP_NET_ADMIN));\n3866:\t\t\tsockopt_release_sock(sk);\n3867:\t\t\treturn err;\n3868:\t\t}\n3869:\t\tcase TCP_ULP: {\n3870:\t\t\tchar name[TCP_ULP_NAME_MAX];\n3871:\t\n3872:\t\t\tif (optlen \u003c 1)\n3873:\t\t\t\treturn -EINVAL;\n3874:\t\n3875:\t\t\tval = strncpy_from_sockptr(name, optval,\n3876:\t\t\t\t\t\tmin_t(long, TCP_ULP_NAME_MAX - 1,\n3877:\t\t\t\t\t\t optlen));\n3878:\t\t\tif (val \u003c 0)\n3879:\t\t\t\treturn -EFAULT;\n" }
53/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25604 output: 37 thoughts: 23 Thoughts: Here's my take on those thoughts: Tracing the Integer Values in `do_tcp_setsockopt` Okay, so I need to understand how integer options are handled within the `do_tcp_setsockopt` function. This suggests that I want to see how this function is parsing and using data from the `setsockopt` system call, particularly when the option value is an integer. Let's start with tracking where the integer values are actually being read into the `val` variable. This will give me a point to begin tracing through how the options get interpreted. I need to understand where the code is vulnerable to something being passed in, or where the code uses it.
54/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 3920, "LineCount": 40 } Results: { "Contents": "3920:\t\t\treturn tcp_sock_set_syncnt(sk, val);\n3921:\t\tcase TCP_USER_TIMEOUT:\n3922:\t\t\treturn tcp_sock_set_user_timeout(sk, val);\n3923:\t\tcase TCP_KEEPINTVL:\n3924:\t\t\treturn tcp_sock_set_keepintvl(sk, val);\n3925:\t\tcase TCP_KEEPCNT:\n3926:\t\t\treturn tcp_sock_set_keepcnt(sk, val);\n3927:\t\tcase TCP_LINGER2:\n3928:\t\t\tif (val \u003c 0)\n3929:\t\t\t\tWRITE_ONCE(tp-\u003elinger2, -1);\n3930:\t\t\telse if (val \u003e TCP_FIN_TIMEOUT_MAX / HZ)\n3931:\t\t\t\tWRITE_ONCE(tp-\u003elinger2, TCP_FIN_TIMEOUT_MAX);\n3932:\t\t\telse\n3933:\t\t\t\tWRITE_ONCE(tp-\u003elinger2, val * HZ);\n3934:\t\t\treturn 0;\n3935:\t\tcase TCP_DEFER_ACCEPT:\n3936:\t\t\t/* Translate value in seconds to number of retransmits /\n3937:\t\t\tWRITE_ONCE(icsk-\u003eicsk_accept_queue.rskq_defer_accept,\n3938:\t\t\t\t secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,\n3939:\t\t\t\t\t\t TCP_RTO_MAX / HZ));\n3940:\t\t\treturn 0;\n3941:\t\tcase TCP_RTO_MAX_MS:\n3942:\t\t\tif (val \u003c MSEC_PER_SEC \|\| val \u003e TCP_RTO_MAX_SEC MSEC_PER_SEC)\n3943:\t\t\t\treturn -EINVAL;\n3944:\t\t\tWRITE_ONCE(inet_csk(sk)-\u003eicsk_rto_max, msecs_to_jiffies(val));\n3945:\t\t\treturn 0;\n3946:\t\tcase TCP_RTO_MIN_US: {\n3947:\t\t\tint rto_min = usecs_to_jiffies(val);\n3948:\t\n3949:\t\t\tif (rto_min \u003e TCP_RTO_MIN \|\| rto_min \u003c TCP_TIMEOUT_MIN)\n3950:\t\t\t\treturn -EINVAL;\n3951:\t\t\tWRITE_ONCE(inet_csk(sk)-\u003eicsk_rto_min, rto_min);\n3952:\t\t\treturn 0;\n3953:\t\t}\n3954:\t\tcase TCP_DELACK_MAX_US: {\n3955:\t\t\tint delack_max = usecs_to_jiffies(val);\n3956:\t\n3957:\t\t\tif (delack_max \u003e TCP_DELACK_MAX \|\| delack_max \u003c TCP_TIMEOUT_MIN)\n3958:\t\t\t\treturn -EINVAL;\n3959:\t\t\tWRITE_ONCE(inet_csk(sk)-\u003eicsk_delack_max, delack_max);\n" }
55/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 26591 output: 37 thoughts: 37 Thoughts: Okay, let's see... I'm looking at this code, and I need to understand how this option value is being handled. The crucial part seems to be how the integer value is retrieved, specifically, the `copy_from_sockptr(&val, optval, sizeof(int))` function call. I need to trace where this is happening. Let me just zero in on that line, 3900 - 3920. That seems like the right section to investigate. This should reveal exactly how that integer, `val`, is being populated from the socket option data. Understanding this is key to understanding the control flow and potential vulnerabilities around this option.
56/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 3890, "LineCount": 35 } Results: { "Contents": "3890:\t\n3891:\t\t\t/* Allow a backup key as well to facilitate key rotation\n3892:\t\t\t * First key is the active one.\n3893:\t\t\t /\n3894:\t\t\tif (optlen != TCP_FASTOPEN_KEY_LENGTH \u0026\u0026\n3895:\t\t\t optlen != TCP_FASTOPEN_KEY_BUF_LENGTH)\n3896:\t\t\t\treturn -EINVAL;\n3897:\t\n3898:\t\t\tif (copy_from_sockptr(key, optval, optlen))\n3899:\t\t\t\treturn -EFAULT;\n3900:\t\n3901:\t\t\tif (optlen == TCP_FASTOPEN_KEY_BUF_LENGTH)\n3902:\t\t\t\tbackup_key = key + TCP_FASTOPEN_KEY_LENGTH;\n3903:\t\n3904:\t\t\treturn tcp_fastopen_reset_cipher(net, sk, key, backup_key);\n3905:\t\t}\n3906:\t\tdefault:\n3907:\t\t\t/ fallthru /\n3908:\t\t\tbreak;\n3909:\t\t}\n3910:\t\n3911:\t\tif (optlen \u003c sizeof(int))\n3912:\t\t\treturn -EINVAL;\n3913:\t\n3914:\t\tif (copy_from_sockptr(\u0026val, optval, sizeof(val)))\n3915:\t\t\treturn -EFAULT;\n3916:\t\n3917:\t\t/ Handle options that can be set without locking the socket. */\n3918:\t\tswitch (optname) {\n3919:\t\tcase TCP_SYNCNT:\n3920:\t\t\treturn tcp_sock_set_syncnt(sk, val);\n3921:\t\tcase TCP_USER_TIMEOUT:\n3922:\t\t\treturn tcp_sock_set_user_timeout(sk, val);\n3923:\t\tcase TCP_KEEPINTVL:\n3924:\t\t\treturn tcp_sock_set_keepintvl(sk, val);\n" }
57/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27320 output: 20 thoughts: 636 Thoughts: ECN Mode and Option Implementation Deep Dive Okay, so I'm looking at how the TCP ECN (Explicit Congestion Notification) mode and options are handled. I see that the value, `val`, which is set via a socket option (using `copy_from_sockptr`), is fully copied, which is good. The check ensures that we're dealing with integers, and that the values for TCP ECN mode and the ECN option fall within their defined ranges. That's standard input validation. The `WRITE_ONCE` construct is also standard, making sure there are no read-write issues. Now, the interesting part is how the "effective" ECN mode and option are determined, using `tcp_ecn_mode_eff` and `tcp_accecn_option_eff`. It's a two-tiered approach. I see that if the per-socket override (`ecn_mode` or `ecn_option`) is unspecified (the value is `TCP_ECN_MODE_UNSPEC` or `TCP_ACCECN_OPTION_UNSPEC`), the system-wide default (from `sysctl_tcp_ecn` and `sysctl_tcp_ecn_option`, respectively) is used. That's a good way to give the user both fine-grained control and a sane default. My immediate question is: could these functions, particularly `tcp_ecn_mode_eff` and `tcp_accecn_option_eff`, or even `cookie_ecn_ok`, ever be called with a `sock` pointer that isn't a fully fledged `tcp_sock`? That would be a serious bug. We're casting `sk` to `tcp_sk(sk)` within these functions, so the potential for a type confusion is high. I need to make sure that assumption holds true everywhere these functions are called. The first place I see this is `cookie_ecn_ok`, which is defined in `net/net/tcp_ecn.h`. This function returns a boolean to determine if ECN is okay or not. Now, let's trace where that's used... I need to grep for `cookie_ecn_ok` in the codebase and check the context of each call to ensure the `sock` pointer always points to an appropriate `tcp_sock` structure. That's where I will start, right now.
58/3	2026/09/17 15:16	tool	grepper	0m Args: { "Expression": "cookie_ecn_ok" } Results: { "Output": "include/net/tcp_ecn.h=48=static inline u8 tcp_accecn_option_eff(const struct sock sk)\n--\ninclude/net/tcp_ecn.h-57-/ ECN support for SYN cookies: per-socket override or route feature /\ninclude/net/tcp_ecn.h:58:static inline bool cookie_ecn_ok(const struct sock sk, const struct dst_entry dst)\ninclude/net/tcp_ecn.h-59-{\n--\nnet/ipv4/syncookies.c=405=struct sock cookie_v4_check(struct sock sk, struct sk_buff skb)\n--\nnet/ipv4/syncookies.c-492-\t\tireq-\u003ercv_wscale = rcv_wscale;\nnet/ipv4/syncookies.c:493:\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, \u0026rt-\u003edst);\nnet/ipv4/syncookies.c-494-\ttreq-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n--\nnet/ipv6/syncookies.c=174=struct sock cookie_v6_check(struct sock sk, struct sk_buff *skb)\n--\nnet/ipv6/syncookies.c-273-\t\tireq-\u003ercv_wscale = rcv_wscale;\nnet/ipv6/syncookies.c:274:\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, dst);\nnet/ipv6/syncookies.c-275-\ttcp_rsk(req)-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n" }
59/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 28942 output: 39 thoughts: 493 Thoughts: Analyzing TCP Socket Usage in ECN Context Okay, so I'm diving into how ECN (Explicit Congestion Notification) is handled within the TCP stack, specifically concerning the use of the listening socket (`sk`). I'm seeing a consistent pattern. In `cookie_v4_check` and `cookie_v6_check`, the variable `sk` represents the listening socket. Critically, these listening sockets are full TCP sockets (instances of `struct tcp_sock`). I've also traced how the socket is used elsewhere. Looking at `tcp_ecn_send_syn` (in `include/net/tcp_ecn.h`), this function explicitly deals with a TCP socket during SYN packet transmission; `sk` is clearly a full TCP socket in that context. Now, let's look at `tcp_ecn_create_request` in `net/ipv4/tcp_input.c`. Here, `listen_sk` is specifically identified as the listening socket, also a full TCP socket. The ECN mode check is performed using `tcp_ecn_mode_eff(listen_sk)`. That's a strong consistency signal. I need to confirm this understanding further. In `net/ipv4/tcp_output.c`, I've observed that functions like `tcp_syn_options`, `tcp_synack_options`, and `tcp_established_options` all call `tcp_accecn_option_eff(sk)`. I can see that in all these cases, `sk` is again a full TCP socket, either a listening socket for the SYNACK or an established TCP socket. This supports my hypothesis. Let me zero in on `tcp_synack_options` in that file, checking the code around line 1133 to ensure I haven't missed something.
60/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "net/ipv4/tcp_output.c", "FirstLine": 1120, "LineCount": 40 } Results: { "Contents": "1120:\t\n1121:\t\t\tneed += foc-\u003eexp ? TCPOLEN_EXP_FASTOPEN_BASE :\n1122:\t\t\t\t\t TCPOLEN_FASTOPEN_BASE;\n1123:\t\t\tneed = (need + 3) \u0026 ~3U; /* Align to 32 bits /\n1124:\t\t\tif (remaining \u003e= need) {\n1125:\t\t\t\topts-\u003eoptions \|= OPTION_FAST_OPEN_COOKIE;\n1126:\t\t\t\topts-\u003efastopen_cookie = foc;\n1127:\t\t\t\tremaining -= need;\n1128:\t\t\t}\n1129:\t\t}\n1130:\t\n1131:\t\tmptcp_set_option_cond(req, opts, \u0026remaining);\n1132:\t\n1133:\t\tsmc_set_option_cond(tcp_sk(sk), ireq, opts, \u0026remaining);\n1134:\t\n1135:\t\tif (treq-\u003eaccecn_ok \u0026\u0026\n1136:\t\t tcp_accecn_option_eff(sk) \u0026\u0026\n1137:\t\t synack_type != TCP_SYNACK_RETRANS \u0026\u0026 remaining \u003e= TCPOLEN_ACCECN_BASE) {\n1138:\t\t\topts-\u003euse_synack_ecn_bytes = 1;\n1139:\t\t\tremaining -= tcp_options_fit_accecn(opts, 0, remaining);\n1140:\t\t}\n1141:\t\n1142:\t\tremaining = bpf_skops_hdr_opt_len((struct sock )sk, skb, req, syn_skb,\n1143:\t\t\t\t\t\t synack_type, opts, remaining);\n1144:\t\n1145:\t\treturn MAX_TCP_OPTION_SPACE - remaining;\n1146:\t}\n1147:\t\n1148:\t/* Compute TCP options for ESTABLISHED sockets. This is not the\n1149:\t * final wire format yet.\n1150:\t /\n1151:\tstatic unsigned int tcp_established_options(struct sock sk, struct sk_buff skb,\n1152:\t\t\t\t\t\tstruct tcp_out_options opts,\n1153:\t\t\t\t\t\tstruct tcp_key key)\n1154:\t{\n1155:\t\tstruct tcp_sock tp = tcp_sk(sk);\n1156:\t\tunsigned int size = 0;\n1157:\t\tunsigned int eff_sacks;\n1158:\t\n1159:\t\topts-\u003eoptions = 0;\n" }
61/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 30515 output: 35 thoughts: 243 Thoughts: Analyzing TCP Socket Option Handling Okay, so I'm looking at this code, specifically line 1133: `smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining);`. The key here is that `sk` in `tcp_synack_options` has already been cast to `tcp_sk(sk)`. This immediately brings up the question of the underlying data structure – specifically, the `struct tcp_sock` layout. I need to refresh my memory on any potential padding issues that might affect how we're accessing data. Let's check `include/linux/tcp.h` to see how the struct is defined. Okay, here it is… I see these new ECN fields, `ecn_flags`, `ecn_mode`, and `ecn_option`. These are pretty recent additions, which is something to bear in mind if there's any legacy code. I need to make sure I understand their positions in the structure to avoid any alignment issues, given that we are working with `tcp_sk`. Specifically, let's examine around line 285 to confirm that these members are positioned as expected and check for any potential unintended side-effects of this addition. I'm focusing on the relationship between the members and potential alignment considerations.
62/3	2026/09/17 15:16	tool	read-file	0m Args: { "File": "include/linux/tcp.h", "FirstLine": 275, "LineCount": 35 } Results: { "Contents": " 275:\t\tu32\tpushed_seq;\t/* Last pushed seq, required to talk to windows /\n 276:\t\tu32\tlsndtime;\t/ timestamp of last sent data packet (for restart window) /\n 277:\t\tu32\tmdev_us;\t/ mean deviation of RTT, scaled by 4 (\u003c\u003c 2) in usecs /\n 278:\t\tu32\trtt_seq;\t/ sequence number to update rttvar\t/\n 279:\t\tu32\tmax_packets_out; / max packets_out in last window /\n 280:\t\tu32\tcwnd_usage_seq; / right edge of cwnd usage tracking flight /\n 281:\t\tu32\trate_delivered; / saved rate sample: packets delivered /\n 282:\t\tu32\trate_interval_us; / saved rate sample: time elapsed /\n 283:\t\tu64\ttcp_wstamp_ns;\t/ departure time for next sent data packet /\n 284:\t\tu64\taccecn_opt_tstamp;\t/ Last AccECN option sent timestamp /\n 285:\t\tstruct list_head tsorted_sent_queue; / time-sorted sent but un-SACKed skbs /\n 286:\t\tstruct sk_buff highest_sack; /* skb just after the highest\n 287:\t\t\t\t\t\t * skb with SACKed bit set\n 288:\t\t\t\t\t\t * (validity guaranteed only if\n 289:\t\t\t\t\t\t * sacked_out \u003e 0)\n 290:\t\t\t\t\t\t /\n 291:\t\tu8\tecn_flags;\t/ ECN status bits.\t\t\t/\n 292:\t\tu8\tecn_mode;\t/ Per-socket ECN mode override\n 293:\t\t\t\t\t * (TCP_ECN_MODE_UNSPEC = use sysctl)\n 294:\t\t\t\t\t /\n 295:\t\tu8\tecn_option;\t/ Per-socket AccECN option override\n 296:\t\t\t\t\t * (TCP_ACCECN_OPTION_UNSPEC = use sysctl)\n 297:\t\t\t\t\t /\n 298:\t\n 299:\t\t__cacheline_group_end(tcp_sock_write_tx);\n 300:\t\n 301:\t\t/ TXRX read-write hotpath cache lines /\n 302:\t\t__cacheline_group_begin(tcp_sock_write_txrx);\n 303:\t/\n 304:\t \tHeader prediction flags\n 305:\t \t0x5?10 \u003c\u003c 16 + snd_wnd in net byte order\n 306:\t /\n 307:\t\tu8\tnonagle : 4,/ Disable Nagle algorithm? /\n 308:\t\t\trate_app_limited:1; / rate_{delivered,interval_us} limited? /\n 309:\t\tu8\treceived_ce_pending:4, / Not yet transmit cnt of received_ce */\n" }
63/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 31830 output: 31 thoughts: 694 Thoughts: ECN Field Analysis in TCP Sockets Okay, let's break this down. I'm looking at the `struct tcp_sock` definition, specifically the ECN-related fields: `ecn_flags`, `ecn_mode`, and `ecn_option`, all represented as `u8` types. My primary concern is data leakage to user space. First, I need to make sure none of these structures are directly copied to user space. I know TCP information is usually retrieved via `tcp_get_info` which populates a `struct tcp_info`. I've checked and neither `ecn_mode` or `ecn_option` are added to the structure. So the data is not copied directly. Now, the important question is how `TCP_ECN` or `TCP_ECN_OPTION` getsockopt calls are handled. I've found the relevant code in `do_tcp_getsockopt`. It shows that `tp->ecn_mode` and `tp->ecn_option` values are read using `READ_ONCE`, and the result, `val`, which is an `int` on the stack is copied to user space via `copy_to_sockptr`. Since the length is less than or equal to the size of an `int`, I know that any uninitialized bytes in `val` are safe, because `val` is fully initialized with the promoted `u8` value. However, I need to confirm that `tp->ecn_mode` is always initialized. I know it's set in `tcp_init_sock` to `TCP_ECN_MODE_UNSPEC`. Just to be sure, I need to verify that `tcp_init_sock` is always called and that the memory allocated for the socket is zeroed or initialized. Checking `tcp_init_sock`, I see `tp->ecn_mode` is indeed explicitly initialized to `TCP_ECN_MODE_UNSPEC`. Further, examining `sock_init_data`, it uses memory zeroing using `GFP_ZERO` or `kzalloc` or `kmem_cache_alloc`, with appropriate constructors/zeroing. I'm confident that the ECN-related fields in `struct tcp_sock` are correctly handled and do not present a data leakage issue.
64/3	2026/09/17 15:16	tool	grepper	0m Args: { "Expression": "sk_alloc\\(", "PathPrefix": "net/core/sock.c" } Results: { "Output": "net/core/sock.c=2237=static struct sock sk_prot_alloc(struct proto prot, gfp_t priority,\n--\nnet/core/sock.c-2253-\tif (sk != NULL) {\nnet/core/sock.c:2254:\t\tif (security_sk_alloc(sk, family, priority))\nnet/core/sock.c-2255-\t\t\tgoto out_free;\n--\nnet/core/sock.c=2273=static void sk_prot_free(struct proto prot, struct sock sk)\n--\nnet/core/sock.c-2301- /\nnet/core/sock.c:2302:struct sock sk_alloc(struct net net, int family, gfp_t priority,\nnet/core/sock.c-2303-\t\t struct proto prot, int kern)\n--\nnet/core/sock.c-2334-\nnet/core/sock.c:2335:\t\tmem_cgroup_sk_alloc(sk);\nnet/core/sock.c:2336:\t\tcgroup_sk_alloc(\u0026sk-\u003esk_cgrp_data);\nnet/core/sock.c-2337-\t\tsock_update_classid(\u0026sk-\u003esk_cgrp_data);\n" }
65/3	2026/09/17 15:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 33387 output: 36 thoughts: 11 Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own: Analyzing `sk_prot_alloc` Right, let's take a look at `sk_prot_alloc`. I need to understand its function, its purpose within the broader networking context, and, crucially, how it contributes to performance and resource management. It's a foundational element, I need to know how it’s implemented and the implications of those methods. I'm thinking about the data structures it manipulates. Are they optimized for cache efficiency? What locking mechanisms are involved, and what's their impact on concurrency? I need to consider the worst-case scenarios and potential bottlenecks. I'm also wondering about the interaction of this function with other parts of the network stack, such as memory management and protocol handlers. Is it tightly coupled? How easy would it be to modify or extend it without introducing subtle bugs? I should see if this is thread-safe and how it interacts with the garbage collector. I'll be looking for any potential areas for optimization, such as lock contention, memory allocation patterns, or inefficient data copying. Perhaps, if I dig deep enough, I might find a subtle optimization opportunity that would give a slight performance boost. Let's see...
66/3	2026/09/17 15:17	tool	read-file	0m Args: { "File": "net/core/sock.c", "FirstLine": 2237, "LineCount": 20 } Results: { "Contents": "2237:\tstatic struct sock sk_prot_alloc(struct proto prot, gfp_t priority,\n2238:\t\t\tint family)\n2239:\t{\n2240:\t\tstruct sock sk;\n2241:\t\tstruct kmem_cache slab;\n2242:\t\n2243:\t\tslab = prot-\u003eslab;\n2244:\t\tif (slab != NULL) {\n2245:\t\t\tsk = kmem_cache_alloc(slab, priority \u0026 ~__GFP_ZERO);\n2246:\t\t\tif (!sk)\n2247:\t\t\t\treturn sk;\n2248:\t\t\tif (want_init_on_alloc(priority))\n2249:\t\t\t\tsk_prot_clear_nulls(sk, prot-\u003eobj_size);\n2250:\t\t} else\n2251:\t\t\tsk = kmalloc(prot-\u003eobj_size, priority);\n2252:\t\n2253:\t\tif (sk != NULL) {\n2254:\t\t\tif (security_sk_alloc(sk, family, priority))\n2255:\t\t\t\tgoto out_free;\n2256:\t\n" }
67/3	2026/09/17 15:17	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 34011 output: 38 thoughts: 1007 Thoughts: ECN Initialization and Propagation: A Deep Dive Okay, so I'm thinking through how ECN (Explicit Congestion Notification) is handled in the TCP stack, particularly concerning its initialization and propagation. Let's trace this from allocation to BPF and sysctl interactions. First, I see `kmem_cache_alloc(slab, priority & ~__GFP_ZERO);` for allocating a `tcp_sock`. This uses the `tcp_sock` slab, and crucially, `tcp_init_sock(sk)` gets called in `inet_create` which leads to `sk->sk_prot->init(sk)`. Specifically, that `sk->sk_prot->init` is `tcp_v4_init_sock`, which then definitely calls `tcp_init_sock(sk)`. Inside `tcp_init_sock`, I see `tp->ecn_mode = TCP_ECN_MODE_UNSPEC;` and `tp->ecn_option = TCP_ACCECN_OPTION_UNSPEC;` which tells me these values are initialized here. Now, the interesting bit: what happens with cloned sockets? `tcp_create_openreq_child` clones by calling `inet_csk_clone_lock(sk, req, GFP_ATOMIC)`, which leads to `sk_clone_lock(sk, priority)`. `sock_copy(newsk, sk)` effectively does a `memcpy` of the socket data including `nsk->sk_prot->obj_size`, so `newtp->ecn_mode` and `newtp->ecn_option` are copied from the parent. That means the initialized values are getting copied. But, are there other places where `tcp_sock` might be initialized or used, and more importantly, how are these ECN values treated? BPF sockops are a prime suspect. Okay, let's look at `net/core/filter.c`. I see `TCP_ECN` and `TCP_ECN_OPTION` explicitly mentioned in `bpf_setsockopt` and `bpf_getsockopt`. This is significant! BPF can use `bpf_setsockopt` and `bpf_getsockopt`. `bpf_getsockopt` for `TCP_ECN` calls `sol_tcp_sockopt` which calls `do_tcp_getsockopt`. The important part here is that when BPF does a `bpf_getsockopt` with `TCP_ECN`, `optlen` is initialized to `sizeof(int)`, the value is read with `READ_ONCE(tp->ecn_mode)` and then copied to `optval` via `copy_to_sockptr`, which is a kernel pointer. Then BPF can get an integer value representing `ecn_mode`. Alright, what about the system-wide sysctl values? I know they exist: `sock_net(sk)->ipv4.sysctl_tcp_ecn` and `sysctl_tcp_ecn_option`. Are these always initialized? Yes, per-netns initialization sets them to the defaults. Finally, let's check the changes in `cookie_ecn_ok`. I'm seeing changes in the inline function. The inline function `cookie_ecn_ok` now takes a `sock` rather than a `net`. And in `net/ipv4/syncookies.c` and `net/ipv6/syncookies.c`, `ireq->ecn_ok` is modified to use this new function. The function is calling `tcp_ecn_mode_eff(sk)`. So, in summary: ECN values are initialized upon socket creation, inherited during cloning, accessible and modifiable via BPF, and influenced by sysctl settings. The changes to `cookie_ecn_ok` are important in the syn-cookie calculation and depend on the current socket settings.
68/3	2026/09/17 15:17	tool	read-file	0m Args: { "File": "net/ipv4/syncookies.c", "FirstLine": 480, "LineCount": 25 } Results: { "Contents": " 480:\t\t (req-\u003ersk_window_clamp \u003e full_space \|\| req-\u003ersk_window_clamp == 0))\n 481:\t\t\treq-\u003ersk_window_clamp = full_space;\n 482:\t\n 483:\t\ttcp_select_initial_window(sk, full_space, req-\u003emss,\n 484:\t\t\t\t\t \u0026req-\u003ersk_rcv_wnd, \u0026req-\u003ersk_window_clamp,\n 485:\t\t\t\t\t ireq-\u003ewscale_ok, \u0026rcv_wscale,\n 486:\t\t\t\t\t dst_metric(\u0026rt-\u003edst, RTAX_INITRWND));\n 487:\t\n 488:\t\t/* req-\u003esyncookie is set true only if ACK is validated\n 489:\t\t * by BPF kfunc, then, rcv_wscale is already configured.\n 490:\t\t /\n 491:\t\tif (!req-\u003esyncookie)\n 492:\t\t\tireq-\u003ercv_wscale = rcv_wscale;\n 493:\t\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, \u0026rt-\u003edst);\n 494:\t\ttreq-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n 495:\t\n 496:\t\tret = tcp_get_cookie_sock(sk, skb, req, \u0026rt-\u003edst);\n 497:\t\t/ ip_queue_xmit() depends on our flow being setup\n 498:\t\t * Normal sockets get it right from inet_csk_route_child_sock()\n 499:\t\t */\n 500:\t\tif (!ret) {\n 501:\t\t\tSKB_DR_SET(reason, NO_SOCKET);\n 502:\t\t\tgoto out_drop;\n 503:\t\t}\n 504:\t\tinet_sk(ret)-\u003ecork.fl.u.ip4 = fl4;\n" }
69/3	2026/09/17 15:17	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 36408 output: 38 thoughts: 62 Thoughts: Analyzing the Cookie Verification Logic Okay, hold on a second. In this `cookie_v4_check` function, I see that this `cookie_ecn_ok` function is taking the listening socket, `sk`, as its first argument. That seems… potentially unusual. It's making me question if I understand the data flow correctly. I need to make sure I'm following the correct execution path through the codebase. Let's quickly cross-reference that with the IPv6 implementation. I should check `cookie_v6_check` function. Where is that defined? Ah, right, in `net/ipv6/syncookies.c`. I'm going to take a closer look there and confirm my assumptions. The IPv4 path might be correct, or I might be missing something fundamental. Gotta get a solid handle on how these syncookies are being validated.
70/3	2026/09/17 15:17	tool	read-file	0m Args: { "File": "net/ipv6/syncookies.c", "FirstLine": 260, "LineCount": 25 } Results: { "Contents": " 260:\t\tif (sk-\u003esk_userlocks \u0026 SOCK_RCVBUF_LOCK \u0026\u0026\n 261:\t\t (req-\u003ersk_window_clamp \u003e full_space \|\| req-\u003ersk_window_clamp == 0))\n 262:\t\t\treq-\u003ersk_window_clamp = full_space;\n 263:\t\n 264:\t\ttcp_select_initial_window(sk, full_space, req-\u003emss,\n 265:\t\t\t\t\t \u0026req-\u003ersk_rcv_wnd, \u0026req-\u003ersk_window_clamp,\n 266:\t\t\t\t\t ireq-\u003ewscale_ok, \u0026rcv_wscale,\n 267:\t\t\t\t\t dst_metric(dst, RTAX_INITRWND));\n 268:\t\n 269:\t\t/* req-\u003esyncookie is set true only if ACK is validated\n 270:\t\t * by BPF kfunc, then, rcv_wscale is already configured.\n 271:\t\t */\n 272:\t\tif (!req-\u003esyncookie)\n 273:\t\t\tireq-\u003ercv_wscale = rcv_wscale;\n 274:\t\tireq-\u003eecn_ok \u0026= cookie_ecn_ok(sk, dst);\n 275:\t\ttcp_rsk(req)-\u003eaccecn_ok = ireq-\u003eecn_ok \u0026\u0026 cookie_accecn_ok(th);\n 276:\t\n 277:\t\tret = tcp_get_cookie_sock(sk, skb, req, dst);\n 278:\t\tif (!ret) {\n 279:\t\t\tSKB_DR_SET(reason, NO_SOCKET);\n 280:\t\t\tgoto out_drop;\n 281:\t\t}\n 282:\tout:\n 283:\t\treturn ret;\n 284:\tout_free:\n" }
71/3	2026/09/17 15:17	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 37166 output: 426 thoughts: 3470 Thoughts: Analysis of ECN Mode and Option Overrides in TCP Sockets Okay, I've thoroughly reviewed the code changes related to introducing per-socket overrides for ECN mode and the AccECN option. My focus was on potential memory safety issues, particularly those that could necessitate a KMSAN run. I traced the usage of `ecn_mode` and `ecn_option`, which are added to the `tcp_sock` structure, across the relevant TCP functions. I examined the `tcp_syn_options`, `tcp_synack_options`, `tcp_established_options`, `tcp_ecn_create_request`, and `tcp_ecn_send_syn` functions, confirming that the code consistently uses the new `tcp_ecn_mode_eff` and `tcp_accecn_option_eff` functions. These functions, in turn, read the `ecn_mode` and `ecn_option` fields. The key here is ensuring that these fields are always initialized before they are read. I dug into the socket option handling using `getsockopt` and `setsockopt` for `TCP_ECN` and `TCP_ECN_OPTION`. I confirmed that the values are initialized by `tcp_init_sock` and can only be modified via `setsockopt`. I also double-checked that `copy_to_sockptr` writes a maximum of 4 bytes with a fully initialized value. I meticulously traced all socket creation paths, confirming that `tcp_init_sock` is always called, initializing the ECN fields during socket creation, and also that sockets are cloned, with the new fields correctly initialized via a copy of the listening socket. I also considered the KMSAN requirements, and the four conditions which could require KMSAN: I checked that there were no kernel structures sent to userspace, conditional logic or branching depending on potentially uninitialized variables, complex data structures with uninitialized fields or bounds checks leading to uninitialized reads. I thoroughly checked `do_tcp_getsockopt` and `do_tcp_setsockopt` and concluded there are no uninitialized memory risks. The new code simply overrides sysctl values in the ECN mode and negotiation code. Finally, I checked all `struct tcp_sock` allocation or creation paths in the kernel. I'm confident that the introduction of `ecn_mode` and `ecn_option` does not introduce any uninitialized memory risks or info-leaks. The code is structured to ensure that these fields are always initialized before use, and that there are no padding-related issues. Standard bug detectors and KASAN should be sufficient to catch any other issues. Based on this, `NeedsKMSAN` should be set to `false`, and I am ready to submit that result.
72/3	2026/09/17 15:17	tool	set-results	0m Args: { "KMSANReasoning": "The patch introduces per-socket configuration for TCP ECN mode (TCP_ECN) and Accurate ECN option sending behavior (TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, adding two u8 fields (ecn_mode and ecn_option) to struct tcp_sock.\n\nAnalysis of uninitialized memory risk:\n1. Field initialization: The new fields `tp-\u003eecn_mode` and `tp-\u003eecn_option` are explicitly initialized in `tcp_init_sock()` to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. Child sockets cloned during incoming connections via `tcp_create_openreq_child()` inherit these fields from the listening socket via `inet_csk_clone_lock()`.\n2. Getsockopt / copy to userspace: In `do_tcp_getsockopt()`, reading `TCP_ECN` or `TCP_ECN_OPTION` reads the u8 value into a local scalar `int val`, which is fully initialized (zero-extended) before `copy_to_sockptr()`. No uninitialized memory or structure padding is exposed or leaked to userspace or BPF.\n3. Setsockopt / input handling: `do_tcp_setsockopt()` validates integer input bounds and writes valid values to the struct fields.\n4. Surrounding logic: The helper functions `tcp_ecn_mode_eff()` and `tcp_accecn_option_eff()` fallback cleanly to the netns sysctl values if the per-socket option is unspecified. No conditional branches operate on uninitialized variables or memory buffers.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not justified. Standard KASAN fuzzing and compiler warnings/UBSAN are sufficient.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch introduces per-socket configuration for TCP ECN mode (TCP_ECN) and Accurate ECN option sending behavior (TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, adding two u8 fields (ecn_mode and ecn_option) to struct tcp_sock.\n\nAnalysis of uninitialized memory risk:\n1. Field initialization: The new fields `tp-\u003eecn_mode` and `tp-\u003eecn_option` are explicitly initialized in `tcp_init_sock()` to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. Child sockets cloned during incoming connections via `tcp_create_openreq_child()` inherit these fields from the listening socket via `inet_csk_clone_lock()`.\n2. Getsockopt / copy to userspace: In `do_tcp_getsockopt()`, reading `TCP_ECN` or `TCP_ECN_OPTION` reads the u8 value into a local scalar `int val`, which is fully initialized (zero-extended) before `copy_to_sockptr()`. No uninitialized memory or structure padding is exposed or leaked to userspace or BPF.\n3. Setsockopt / input handling: `do_tcp_setsockopt()` validates integer input bounds and writes valid values to the struct fields.\n4. Surrounding logic: The helper functions `tcp_ecn_mode_eff()` and `tcp_accecn_option_eff()` fallback cleanly to the netns sysctl values if the per-socket option is unspecified. No conditional branches operate on uninitialized variables or memory buffers.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN fuzzing session is not justified. Standard KASAN fuzzing and compiler warnings/UBSAN are sufficient.", "NeedsKMSAN": false }

LLM Calls Summary:
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Tool Calls Summary:
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