AI Trajectory

Trajectory: (Expand/Collapse All)
Seq	Timestamp	Type	Name	Duration
0/0	2026/09/10 09:06	flow	patch-triage	1m Args: null Results: { "EnableConfigs": [ "INET", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "tcp_conn_request", "tcp_make_synack", "tcp_connect" ], "KMSANReasoning": "The patch adds per-socket ECN and AccECN configuration options (TCP_ECN and TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, overriding the global sysctls.\n\nKMSAN applicability analysis:\n- The new fields `ecn_mode` and `ecn_option` in `struct tcp_sock` are explicitly initialized to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` in `tcp_init_sock()` and copied across socket clones.\n- In `do_tcp_getsockopt()`, reading these fields initializes the full `int val` before `copy_to_sockptr()` copies the data to user space. No struct padding or uninitialized stack bytes are exposed to user space.\n- No uninitialized variables, conditional branches on uninitialized memory, or buffer length manipulations that could expose uninitialized memory are introduced.\n\nTherefore, dedicated KMSAN fuzzing is not required as the changes present no uninitialized memory risks.", "NeedsKMSAN": false, "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options to allow per-socket configuration and override of the tcp_ecn and tcp_ecn_option sysctl settings. It modifies TCP socket options handling (getsockopt/setsockopt), BPF sockopt filters, TCP SYN/SYN-ACK option generation, and TCP connection request processing in the core IPv4/TCP networking stack.", "WorthFuzzing": true }
1/1	2026/09/10 09:06	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit 6304d04c637bcb4a0e424ee4f754d834a3992015\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Thu Sep 10 09:06:13 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_ecn.h b/include/net/tcp_ecn.h\nindex 865d5c5a7718d..931e0877176c7 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 +31,29 @@ 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 = 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 = 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 /* 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 +621,7 @@ 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/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/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/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	2026/09/10 09:06	agent	patch-evaluator	0m Model: core Args: null Results: { "EnableConfigs": [ "INET", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "tcp_conn_request", "tcp_make_synack", "tcp_connect" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options to allow per-socket configuration and override of the tcp_ecn and tcp_ecn_option sysctl settings. It modifies TCP socket options handling (getsockopt/setsockopt), BPF sockopt filters, TCP SYN/SYN-ACK option generation, and TCP connection request processing in the core IPv4/TCP networking stack.", "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 6304d04c637bcb4a0e424ee4f754d834a3992015 Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 10 09:06:13 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_ecn.h b/include/net/tcp_ecn.h index 865d5c5a7718d..931e0877176c7 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 +31,29 @@ 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 = 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 = tcp_sk(sk)->ecn_option; + + if (opt == TCP_ACCECN_OPTION_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + return opt; +} + /* 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 +621,7 @@ 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/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/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/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	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 8278 output: 30 thoughts: 777 Thoughts: Patch Analysis & Fuzzing Strategy Okay, let's dive into this patch. My initial assessment is that this is quite promising for fuzzing. It introduces new socket options, `TCP_ECN` and `TCP_ECN_OPTION`, essentially allowing per-socket overrides for ECN-related sysctl settings. This per-socket granularity immediately flags it as a potential target. The fact that it's interacting with the TCP stack via `setsockopt` and `getsockopt` makes it very accessible. We have user-level interaction right there, and that's exactly what we want. Specifically, I see changes impacting documentation, the core `tcp_sock` structure, header files, and the critical `filter.c` (that's a good sign for BPF interactions), along with numerous core TCP modules: `tcp.c`, `tcp_input.c`, and `tcp_output.c`. This is all core networking code, so yes, without a doubt, `WorthFuzzing = true`. Now, time to refine the approach. First, I need to pinpoint relevant configurations. I’ll need to figure out which configs are crucial for enabling these features. My initial guesses are `INET` (or `NET`) - that seems like a given, and I should check `net/ipv4/Kconfig` and `net/Kconfig` for related TCP configurations. Since we’re dealing with `filter.c`, I should also keep an eye out for `BPF_SYSCALL`, `NET`, and `INET` related configurations. I should check `net/ipv4/Makefile` or `net/ipv4/Kconfig` to see which configurations are needed to build `tcp.c`, `tcp_input.c`, and `tcp_output.c`. This will give me a better understanding of the build environment required for these changes. Then, I'll need to identify the key symbols in this area. From the patch, it looks like `tcp_ecn_mode_eff(sk)` and `tcp_accecn_option_eff(sk)` are worth highlighting, along with `do_tcp_setsockopt` and `do_tcp_getsockopt`. I'll need to analyze these in more depth to target them effectively.
4/2	2026/09/10 09:06	tool	grepper	0m Args: { "Expression": "obj-.tcp\\.o", "PathPrefix": "net/ipv4" } Results:* { "Output": "net/ipv4/Makefile=50=obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o\nnet/ipv4/Makefile:51:obj-$(CONFIG_TCP_CONG_DCTCP) += tcp_dctcp.o\nnet/ipv4/Makefile-52-obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o\n--\nnet/ipv4/Makefile=54=obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o\nnet/ipv4/Makefile:55:obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o\nnet/ipv4/Makefile-56-obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o\n" }
5/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 9772 output: 32 thoughts: 12 Thoughts: Here's a summary of my thought process, as if I were the one thinking it: Diving into the IPv4 Makefile Alright, time to get my hands dirty. I need to understand something related to the IPv4 stack, so let's start by examining the core build instructions. Specifically, I'm heading straight for `net/ipv4/Makefile`. That's where I'll likely find the rules and dependencies for compiling IPv4-related modules and the core IPv4 stack itself. This file will tell me how everything fits together – the object files, the include paths, and any specific compiler flags being used. I expect to see definitions for variables like `obj-$(CONFIG_SOMETHING)` which will guide the inclusion or exclusion of certain features based on kernel configuration. Understanding this Makefile is crucial for tracing the build process and identifying the impact of any changes I make, or for understanding the build context of some other module I'm looking at. Hopefully, this will be the starting point I need to solve the problem I'm looking at.
6/2	2026/09/10 09:06	tool	read-file	0m Args: { "File": "net/ipv4/Makefile", "FirstLine": 1, "LineCount": 50 } Results: { "Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0\n 2:\t#\n 3:\t# Makefile for the Linux TCP/IP (INET) layer.\n 4:\t#\n 5:\t\n 6:\tobj-y := route.o inetpeer.o protocol.o \\\n 7:\t\t ip_input.o ip_fragment.o ip_forward.o ip_options.o \\\n 8:\t\t ip_output.o ip_sockglue.o inet_hashtables.o \\\n 9:\t\t inet_timewait_sock.o inet_connection_sock.o \\\n 10:\t\t tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \\\n 11:\t\t tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \\\n 12:\t\t tcp_recovery.o tcp_ulp.o \\\n 13:\t\t tcp_offload.o tcp_plb.o datagram.o raw.o udp.o \\\n 14:\t\t udp_offload.o arp.o icmp.o devinet.o af_inet.o igmp.o \\\n 15:\t\t fib_frontend.o fib_semantics.o fib_trie.o fib_notifier.o \\\n 16:\t\t inet_fragment.o ping.o ip_tunnel_core.o gre_offload.o \\\n 17:\t\t metrics.o netlink.o nexthop.o udp_tunnel_stub.o\n 18:\t\n 19:\tobj-$(CONFIG_NET_IP_TUNNEL) += ip_tunnel.o\n 20:\tobj-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o\n 21:\tobj-$(CONFIG_PROC_FS) += proc.o\n 22:\tobj-$(CONFIG_IP_MULTIPLE_TABLES) += fib_rules.o\n 23:\tobj-$(CONFIG_IP_MROUTE) += ipmr.o\n 24:\tobj-$(CONFIG_IP_MROUTE_COMMON) += ipmr_base.o\n 25:\tobj-$(CONFIG_NET_IPIP) += ipip.o\n 26:\tgre-y := gre_demux.o\n 27:\tfou-y := fou_core.o fou_nl.o fou_bpf.o\n 28:\tobj-$(CONFIG_NET_FOU) += fou.o\n 29:\tobj-$(CONFIG_NET_IPGRE_DEMUX) += gre.o\n 30:\tobj-$(CONFIG_NET_IPGRE) += ip_gre.o\n 31:\tudp_tunnel-y := udp_tunnel_core.o udp_tunnel_nic.o\n 32:\tobj-$(CONFIG_NET_UDP_TUNNEL) += udp_tunnel.o\n 33:\tobj-$(CONFIG_NET_IPVTI) += ip_vti.o\n 34:\tobj-$(CONFIG_SYN_COOKIES) += syncookies.o\n 35:\tobj-$(CONFIG_INET_AH) += ah4.o\n 36:\tobj-$(CONFIG_INET_ESP) += esp4.o\n 37:\tobj-$(CONFIG_INET_ESP_OFFLOAD) += esp4_offload.o\n 38:\tobj-$(CONFIG_INET_IPCOMP) += ipcomp.o\n 39:\tobj-$(CONFIG_INET_XFRM_TUNNEL) += xfrm4_tunnel.o\n 40:\tobj-$(CONFIG_INET_TUNNEL) += tunnel4.o\n 41:\tobj-$(CONFIG_IP_PNP) += ipconfig.o\n 42:\tobj-$(CONFIG_NETFILTER)\t+= netfilter.o netfilter/\n 43:\tobj-$(CONFIG_INET_DIAG) += inet_diag.o\n 44:\tobj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o\n 45:\tobj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o\n 46:\tobj-$(CONFIG_INET_RAW_DIAG) += raw_diag.o\n 47:\tobj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o\n 48:\tobj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o\n 49:\tobj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o\n 50:\tobj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o\n" }
7/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11172 output: 25 thoughts: 21 Thoughts: Here's my summary, as if I were thinking these thoughts: Examining the Network Stack Build Process Okay, so I need to understand exactly how this `net/ipv4` component is being built within the larger kernel framework. The best place to start, as always, is the `net/Makefile`. That's where the magic happens, the orchestrator of dependencies and build rules for this part of the network stack. I need to trace through it and see how `ipv4` is specifically incorporated, to see if there are any gotchas and dependencies that need to be considered. Let's dig in and see what `net/Makefile` reveals.
8/2	2026/09/10 09:06	tool	grepper	0m Args: { "Expression": "ipv4", "PathPrefix": "net/Makefile" } Results: { "Output": "net/Makefile=16=obj-$(CONFIG_NETFILTER)\t\t+= netfilter/\nnet/Makefile:17:obj-$(CONFIG_INET)\t\t+= ipv4/\nnet/Makefile-18-obj-$(CONFIG_TLS)\t\t+= tls/\n" }
9/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11430 output: 33 thoughts: 67 Thoughts: My Initial Code Configuration Thoughts Okay, so I'm diving into this and immediately see a dependency issue. It looks like I absolutely need `CONFIG_INET` enabled if I'm going to touch anything in `net/ipv4/`. That's not surprising, but it's good to make a note of it right away. More specifically though, I'm concerned about the `sol_tcp_sockopt` function in `net/core/filter.c`. I recall that one uses a BPF sockopt helper of sorts. So, if I'm going to work with that, I'm going to need to ensure that `CONFIG_BPF_SYSCALL` is also enabled. Seems pretty straightforward, but I'll make sure to verify those dependencies before proceeding. I'm going to go straight to `net/core/filter.c` to confirm my suspicion. Let's see what's there...
10/2	2026/09/10 09:06	tool	grepper	0m Args: { "Expression": "sol_tcp_sockopt", "PathPrefix": "net/core/filter.c" } Results: { "Output": "net/core/filter.c=5549=static int bpf_sol_tcp_setsockopt(struct sock sk, int optname,\n--\nnet/core/filter.c-5599-\nnet/core/filter.c:5600:static int sol_tcp_sockopt_congestion(struct sock sk, char optval,\nnet/core/filter.c-5601-\t\t\t\t int optlen, bool getopt)\n--\nnet/core/filter.c-5652-\nnet/core/filter.c:5653:static int sol_tcp_sockopt(struct sock sk, int optname,\nnet/core/filter.c-5654-\t\t\t char optval, int optlen,\n--\nnet/core/filter.c-5678-\tcase TCP_CONGESTION:\nnet/core/filter.c:5679:\t\treturn sol_tcp_sockopt_congestion(sk, optval, optlen, getopt);\nnet/core/filter.c-5680-\tcase TCP_SAVED_SYN:\n--\nnet/core/filter.c=5779=static int __bpf_setsockopt(struct sock sk, int level, int optname,\n--\nnet/core/filter.c-5791-\telse if (IS_ENABLED(CONFIG_INET) \u0026\u0026 level == SOL_TCP)\nnet/core/filter.c:5792:\t\treturn sol_tcp_sockopt(sk, optname, optval, \u0026optlen, false);\nnet/core/filter.c-5793-\n--\nnet/core/filter.c=5810=static int __bpf_getsockopt(struct sock *sk, int level, int optname,\n--\nnet/core/filter.c-5822-\telse if (IS_ENABLED(CONFIG_INET) \u0026\u0026 level == SOL_TCP)\nnet/core/filter.c:5823:\t\terr = sol_tcp_sockopt(sk, optname, optval, \u0026optlen, true);\nnet/core/filter.c-5824-\telse if (IS_ENABLED(CONFIG_INET) \u0026\u0026 level == SOL_IP)\n" }
11/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 12276 output: 30 thoughts: 296 Thoughts: Analyzing TCP/IP and BPF Interactions Okay, let's break this down. First, I need to consider the configuration options at play here: `CONFIG_INET` and `CONFIG_BPF_SYSCALL`. Or, potentially, just `CONFIG_INET` might be enough context depending on the specific implementation. Now, the real meat of the analysis lies in the function calls. I need to understand how the code I'm looking at modifies (or is modified by) the logic. My focus is going to be on these specific functions: `do_tcp_setsockopt` and `do_tcp_getsockopt`, which are the primary functions for getting and setting socket options and are located in `net/ipv4/tcp.c`. It's possible I'll see some naming variations on them but the functionality is the key here. Then we have `tcp_ecn_create_request`, `tcp_syn_options`, `tcp_synack_options`, and `tcp_established_options`, all in `net/ipv4/tcp_input.c` or `net/ipv4/tcp_output.c`. Those touch on the TCP ECN, SYN, and established connection options. Finally, `sol_tcp_sockopt` in `net/core/filter.c` is going to be crucial since it's involved in handling socket options at the socket level. The last one to look at is `tcp_ecn_send_syn`, which is a static inline function in `include/net/tcp_ecn.h`. This means I need to quickly identify where this is actually used to see the context surrounding it. Essentially, I need to trace the call paths to understand the full picture of the changes related to the configuration options.
12/2	2026/09/10 09:06	tool	grepper	0m Args: { "Expression": "tcp_ecn_send_syn", "PathPrefix": "net/" } Results: { "Output": "net/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" }
13/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 13247 output: 30 thoughts: 34 Thoughts: Here's my take on the thought process, as if it were my own: Investigating the TCP ECN Synchronization Sequence Okay, so `tcp_connect` triggers `tcp_ecn_send_syn`. That's the expected path – the connection establishment process initiates the ECN-specific SYN flag. But I need to understand this better. It’s not just about what happens, but why. So, I want to trace the dependencies. Let's see who is responsible for calling `tcp_ecn_create_request`, which, I'm guessing, sets up the preconditions for `tcp_ecn_send_syn` to work, or possibly even the flags themselves. Understanding the callgraph here will give me a more complete picture of the ECN implementation within the TCP stack, particularly its integration within the connection setup. This will help me see if the ECN code is integrated cleanly or if there are unexpected interactions. Let's dive into the code and figure out the broader context.
14/2	2026/09/10 09:06	tool	grepper	0m Args: { "Expression": "tcp_ecn_create_request", "PathPrefix": "net/" } 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" }
15/2	2026/09/10 09:06	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 13774 output: 32 thoughts: 47 Thoughts: Okay, here's my take on those thoughts, framed as my own: Digging into TCP Connection Establishment Alright, so I'm thinking through the TCP connection process, and the first thing that jumps out is that `tcp_conn_request` triggers `tcp_ecn_create_request`. I need to remember what's going on there with ECN – definitely something worth reviewing. The connection request is the starting point, and I need to understand this interaction. Then, my mind wanders towards the SYN exchange, and I immediately want to understand how options are handled. I need to refresh my understanding of how the different TCP options are negotiated during connection establishment. Specifically, I need to know where `tcp_syn_options`, `tcp_synack_options`, and `tcp_established_options` are called. This would provide me insight into how these options are used throughout the entire connection's lifecycle. Understanding the "who" and "why" of those calls will give me a better grasp of the TCP stack's logic. Time to dive deeper and trace those calls!
16/2	2026/09/10 09:07	tool	grepper	0m Args: { "Expression": "tcp_(syn\|synack\|established)_options", "PathPrefix": "net/" } 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_ao.c-1399-\t \t\t\t- 2 * TCPOLEN_SACK_PERBLOCK) = 8 (maclen = 4),\nnet/ipv4/tcp_ao.c:1400:\t * see tcp_established_options().\nnet/ipv4/tcp_ao.c-1401-\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-1150- /\nnet/ipv4/tcp_output.c:1151:static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb,\nnet/ipv4/tcp_output.c-1152-\t\t\t\t\tstruct tcp_out_options opts,\n--\nnet/ipv4/tcp_output.c-1191-\nnet/ipv4/tcp_output.c:1192:\t\topt_size = mptcp_established_options(sk, skb, remaining, has_ts,\nnet/ipv4/tcp_output.c-1193-\t\t\t\t\t\t \u0026opts-\u003emptcp);\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 {\nnet/ipv4/tcp_output.c:1582:\t\ttcp_options_size = tcp_established_options(sk, skb, \u0026opts, \u0026key);\nnet/ipv4/tcp_output.c-1583-\t\t/ Force a PSH flag on all (GSO) packets to expedite GRO flush\n--\nnet/ipv4/tcp_output.c=2103=unsigned int tcp_current_mss(struct sock sk)\n--\nnet/ipv4/tcp_output.c-2119-\ttcp_get_current_key(sk, \u0026key);\nnet/ipv4/tcp_output.c:2120:\theader_len = tcp_established_options(sk, NULL, \u0026opts, \u0026key) +\nnet/ipv4/tcp_output.c-2121-\t\t sizeof(struct tcphdr);\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--\nnet/mptcp/options.c=422=void mptcp_get_options(const struct sk_buff skb,\n--\nnet/mptcp/options.c-463-\nnet/mptcp/options.c:464:bool mptcp_syn_options(struct sock sk, const struct sk_buff skb,\nnet/mptcp/options.c-465-\t\t unsigned int size, struct mptcp_out_options opts)\n--\nnet/mptcp/options.c-469-\t/ we will use snd_isn to detect first pkt [re]transmission\nnet/mptcp/options.c:470:\t * in mptcp_established_options_mp()\nnet/mptcp/options.c-471-\t /\n--\nnet/mptcp/options.c=503=static void clear_3rdack_retransmission(struct sock sk)\n--\nnet/mptcp/options.c-511-\nnet/mptcp/options.c:512:static bool mptcp_established_options_mp(struct sock sk, struct sk_buff skb,\nnet/mptcp/options.c-513-\t\t\t\t\t bool snd_data_fin_enable, int size,\n--\nnet/mptcp/options.c-525-\t tell the caller to defer the estimate to\nnet/mptcp/options.c:526:\t * mptcp_established_options_dss(), which will reserve enough space.\nnet/mptcp/options.c-527-\t /\n--\nnet/mptcp/options.c=596=static void mptcp_write_data_fin(struct mptcp_subflow_context subflow,\n--\nnet/mptcp/options.c-623-\nnet/mptcp/options.c:624:static bool mptcp_established_options_dss(struct sock sk, struct sk_buff skb,\nnet/mptcp/options.c-625-\t\t\t\t\t bool snd_data_fin_enable, int size,\n--\nnet/mptcp/options.c=692=static u64 add_addr_generate_hmac(u64 key1, u64 key2,\n--\nnet/mptcp/options.c-718-\nnet/mptcp/options.c:719:static bool mptcp_established_options_add_addr(struct sock sk,\nnet/mptcp/options.c-720-\t\t\t\t\t struct sk_buff skb, int size,\n--\nnet/mptcp/options.c-759-\nnet/mptcp/options.c:760:static bool mptcp_established_options_rm_addr(struct sock sk, int size,\nnet/mptcp/options.c-761-\t\t\t\t\t unsigned int remaining,\n--\nnet/mptcp/options.c-781-\nnet/mptcp/options.c:782:static bool mptcp_established_options_mp_prio(struct sock sk, int size,\nnet/mptcp/options.c-783-\t\t\t\t\t unsigned int remaining,\n--\nnet/mptcp/options.c-806-\nnet/mptcp/options.c:807:static noinline bool mptcp_established_options_rst(struct sock sk,\nnet/mptcp/options.c-808-\t\t\t\t\t\t int size,\n--\nnet/mptcp/options.c-825-\nnet/mptcp/options.c:826:static bool mptcp_established_options_fastclose(struct sock sk, int size,\nnet/mptcp/options.c-827-\t\t\t\t\t\tunsigned int remaining,\n--\nnet/mptcp/options.c-847-\nnet/mptcp/options.c:848:static bool mptcp_established_options_mp_fail(struct sock sk, int size,\nnet/mptcp/options.c-849-\t\t\t\t\t unsigned int remaining,\n--\nnet/mptcp/options.c-869-\nnet/mptcp/options.c:870:int mptcp_established_options(struct sock sk, struct sk_buff skb,\nnet/mptcp/options.c-871-\t\t\t unsigned int remaining, bool has_ts,\n--\nnet/mptcp/options.c-889-\tif (unlikely(skb \u0026\u0026 TCP_SKB_CB(skb)-\u003etcp_flags \u0026 TCPHDR_RST)) {\nnet/mptcp/options.c:890:\t\tif (mptcp_established_options_fastclose(sk, \u0026opt_size, remaining, opts) \|\|\nnet/mptcp/options.c:891:\t\t mptcp_established_options_mp_fail(sk, \u0026opt_size, remaining, opts)) {\nnet/mptcp/options.c-892-\t\t\ttotal_size += opt_size;\n--\nnet/mptcp/options.c-895-\t\t/* MP_RST can be used with MP_FASTCLOSE and MP_FAIL if there is room /\nnet/mptcp/options.c:896:\t\tif (mptcp_established_options_rst(sk, \u0026opt_size, remaining, opts)) {\nnet/mptcp/options.c-897-\t\t\ttotal_size += opt_size;\n--\nnet/mptcp/options.c-903-\tsnd_data_fin = mptcp_data_fin_enabled(msk);\nnet/mptcp/options.c:904:\tif (mptcp_established_options_mp(sk, skb, snd_data_fin, \u0026opt_size, opts))\nnet/mptcp/options.c-905-\t\tret = true;\nnet/mptcp/options.c:906:\telse if (mptcp_established_options_dss(sk, skb, snd_data_fin, \u0026opt_size, opts)) {\nnet/mptcp/options.c-907-\t\tint mp_fail_size;\n--\nnet/mptcp/options.c-909-\t\tret = true;\nnet/mptcp/options.c:910:\t\tif (mptcp_established_options_mp_fail(sk, \u0026mp_fail_size,\nnet/mptcp/options.c-911-\t\t\t\t\t\t remaining - opt_size, opts)) {\n--\nnet/mptcp/options.c-925-\tremaining -= opt_size;\nnet/mptcp/options.c:926:\tif (mptcp_established_options_add_addr(sk, skb, \u0026opt_size, remaining,\nnet/mptcp/options.c-927-\t\t\t\t\t has_ts, opts)) {\n--\nnet/mptcp/options.c-930-\t\tret = true;\nnet/mptcp/options.c:931:\t} else if (mptcp_established_options_rm_addr(sk, \u0026opt_size, remaining, opts)) {\nnet/mptcp/options.c-932-\t\ttotal_size += opt_size;\n--\nnet/mptcp/options.c-936-\nnet/mptcp/options.c:937:\tif (mptcp_established_options_mp_prio(sk, \u0026opt_size, remaining, opts)) {\nnet/mptcp/options.c-938-\t\ttotal_size += opt_size;\n--\nnet/mptcp/options.c-945-\nnet/mptcp/options.c:946:bool mptcp_synack_options(const struct request_sock req, unsigned int size,\nnet/mptcp/options.c-947-\t\t\t struct mptcp_out_options opts)\n--\nnet/mptcp/options.c=1470=void mptcp_write_options(struct tcphdr th, __be32 ptr, struct tcp_sock tp,\n--\nnet/mptcp/options.c-1495-\t \nnet/mptcp/options.c:1496:\t * The same applies in mptcp_established_options() function.\nnet/mptcp/options.c-1497-\t /\n--\nnet/mptcp/options.c-1532-\nnet/mptcp/options.c:1533:\t\t\t/ DSS option is set only by mptcp_established_options,\nnet/mptcp/options.c-1534-\t\t\t * the caller is __tcp_transmit_skb() and ssk is always\n" }
17/2	2026/09/10 09:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 17754 output: 57 thoughts: 85 Thoughts: Examining TCP Socket Options Okay, let's dive into this. I need to understand how TCP socket options are being set and retrieved. My initial focus is on `do_tcp_setsockopt` and `do_tcp_getsockopt`. I remember these functions being key in the `net/ipv4/tcp.c` file, so that's where I'll start. First, a quick check on `do_tcp_setsockopt`… Ah, it's static. That means it's only accessible within this specific file. Now, to trace its usage, I'll need to figure out how `tcp_setsockopt` calls this. Next, I need to understand if `tcp_setsockopt` is static or exported. That will tell me how externally accessible this functionality is. I need to know the scope of this.
18/2	2026/09/10 09:07	tool	grepper	0m Args: { "Expression": "(tcp_setsockopt\|do_tcp_setsockopt\|tcp_getsockopt\|do_tcp_getsockopt)", "PathPrefix": "net/ipv4/tcp.c" } Results: { "Output": "net/ipv4/tcp.c=3823=int tcp_sock_set_maxseg(struct sock sk, int val)\n--\nnet/ipv4/tcp.c-3838- /\nnet/ipv4/tcp.c:3839:int do_tcp_setsockopt(struct sock sk, int level, int optname,\nnet/ipv4/tcp.c-3840-\t\t sockptr_t optval, unsigned int optlen)\n--\nnet/ipv4/tcp.c-4185-\nnet/ipv4/tcp.c:4186:int tcp_setsockopt(struct sock sk, int level, int optname, sockptr_t optval,\nnet/ipv4/tcp.c-4187-\t\t unsigned int optlen)\n--\nnet/ipv4/tcp.c-4194-\t\t\t\t\t\t\t\toptval, optlen);\nnet/ipv4/tcp.c:4195:\treturn do_tcp_setsockopt(sk, level, optname, optval, optlen);\nnet/ipv4/tcp.c-4196-}\n--\nnet/ipv4/tcp.c=4423=struct sk_buff tcp_get_timestamping_opt_stats(const struct sock sk,\n--\nnet/ipv4/tcp.c-4494-\nnet/ipv4/tcp.c:4495:int do_tcp_getsockopt(struct sock sk, int level,\nnet/ipv4/tcp.c-4496-\t\t int optname, sockptr_t optval, sockptr_t optlen)\n--\nnet/ipv4/tcp.c=4876=bool tcp_bpf_bypass_getsockopt(int level, int optname)\nnet/ipv4/tcp.c-4877-{\nnet/ipv4/tcp.c:4878:\t/ TCP do_tcp_getsockopt has optimized getsockopt implementation\nnet/ipv4/tcp.c-4879-\t * to avoid extra socket lock for TCP_ZEROCOPY_RECEIVE.\n--\nnet/ipv4/tcp.c-4886-\nnet/ipv4/tcp.c:4887:int tcp_getsockopt(struct sock sk, int level, int optname, char __user optval,\nnet/ipv4/tcp.c-4888-\t\t int __user *optlen)\n--\nnet/ipv4/tcp.c-4895-\t\t\t\t\t\t\t\toptval, optlen);\nnet/ipv4/tcp.c:4896:\treturn do_tcp_getsockopt(sk, level, optname, USER_SOCKPTR(optval),\nnet/ipv4/tcp.c-4897-\t\t\t\t USER_SOCKPTR(optlen));\n" }
19/2	2026/09/10 09:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 18772 output: 50 thoughts: 163 Thoughts: Analyzing TCP Socket Options in the Linux Kernel Okay, so I'm diving into some TCP implementation details within the kernel. My initial focus is on the socket option handling, specifically the functions `do_tcp_setsockopt` and `do_tcp_getsockopt`. They're both defined in `net/ipv4/tcp.c`, and importantly, they're non-static functions. That's a good starting point, meaning they're potentially accessible from other parts of the kernel. Next, I wanted to understand how a TCP socket is initialized, so I checked `tcp_init_sock` in the same file. It's also non-static, which makes sense; this initialization function would likely be called from a range of places. Now, I switched gears slightly and examined a function related to Explicit Congestion Notification (ECN): `tcp_ecn_create_request` within `net/ipv4/tcp_input.c`. Ah, this one's static. Okay, so it's only visible within the `tcp_input.c` file. Its non-static caller is `tcp_conn_request`, so I see how it interacts with the rest of the code. Finally, I'm shifting my perspective to the output side of TCP, in `net/ipv4/tcp_output.c`, to investigate how SYN, SYN-ACK, and established TCP options are handled. I'll need to check the attributes of `tcp_syn_options`, `tcp_synack_options`, and `tcp_established_options`. Are these static or non-static? That'll give me a clearer picture of their scope and how they are used within the TCP stack.
20/2	2026/09/10 09:07	tool	grepper	0m Args: { "Expression": "(tcp_syn_options\|tcp_synack_options\|tcp_established_options)", "PathPrefix": "net/ipv4/tcp_output.c" } Results: { "Output": "net/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-1150- /\nnet/ipv4/tcp_output.c:1151:static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb,\nnet/ipv4/tcp_output.c-1152-\t\t\t\t\tstruct tcp_out_options opts,\n--\nnet/ipv4/tcp_output.c-1191-\nnet/ipv4/tcp_output.c:1192:\t\topt_size = mptcp_established_options(sk, skb, remaining, has_ts,\nnet/ipv4/tcp_output.c-1193-\t\t\t\t\t\t \u0026opts-\u003emptcp);\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 {\nnet/ipv4/tcp_output.c:1582:\t\ttcp_options_size = tcp_established_options(sk, skb, \u0026opts, \u0026key);\nnet/ipv4/tcp_output.c-1583-\t\t/ Force a PSH flag on all (GSO) packets to expedite GRO flush\n--\nnet/ipv4/tcp_output.c=2103=unsigned int tcp_current_mss(struct sock sk)\n--\nnet/ipv4/tcp_output.c-2119-\ttcp_get_current_key(sk, \u0026key);\nnet/ipv4/tcp_output.c:2120:\theader_len = tcp_established_options(sk, NULL, \u0026opts, \u0026key) +\nnet/ipv4/tcp_output.c-2121-\t\t sizeof(struct tcphdr);\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" }
21/2	2026/09/10 09:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 20632 output: 171 thoughts: 472 Thoughts: Analyzing the TCP ECN Implementation Okay, let's break this down. First, I see a clear trace of the new ECN logic weaving its way through the TCP stack. `tcp_make_synack` calls `tcp_synack_options`, and `tcp_current_mss` calls `tcp_established_options`. We've got `__tcp_transmit_skb` pulling in both `tcp_syn_options` and `tcp_established_options`. Furthermore, `tcp_conn_request` now utilizes `tcp_ecn_create_request`, which makes sense. Then we have the `do_tcp_setsockopt` and `do_tcp_getsockopt` functions directly handling socket option interactions. And, of course, the ever-present `tcp_init_sock`. Now, the important part: I need to identify the key functions that have been modified or introduced related to ECN. I'll flag `tcp_setsockopt`, `tcp_getsockopt`, `do_tcp_setsockopt`, `do_tcp_getsockopt`, `tcp_make_synack`, and `tcp_conn_request` as FocusSymbols. Are any of these functions ubiquitous within the code? Specifically, `do_tcp_setsockopt`, `do_tcp_getsockopt`, `tcp_make_synack`, and `tcp_conn_request` are definitely more specific to the ECN implementation logic than some of the other generic functions. Next, I need to confirm the configuration requirements. `INET` is the foundational requirement. We are also going to need `BPF_SYSCALL` for BPF sockopt helper support. Alright, let's do a sanity check on everything: This is a worthwhile patch to fuzz. It adds `TCP_ECN` and `TCP_ECN_OPTION` socket options. That's good. We are effectively introducing per-socket overrides of `tcp_ecn` and `tcp_ecn_option`, which should allow for granular control over ECN and AccECN behavior. The patch touches socket initialization, setsockopt/getsockopt handlers, BPF sockopt filters, SYN/SYN-ACK option building, and connection request handling. All key parts. The FocusSymbols are: `do_tcp_setsockopt`, `do_tcp_getsockopt`, `tcp_conn_request`, `tcp_make_synack`, and `tcp_connect`. The EnabledConfigs are `INET` and `BPF_SYSCALL`. Now, let's call `set-results`.
22/2	2026/09/10 09:07	tool	set-results	0m Args: { "EnableConfigs": [ "INET", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "tcp_conn_request", "tcp_make_synack", "tcp_connect" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options to allow per-socket configuration and override of the tcp_ecn and tcp_ecn_option sysctl settings. It modifies TCP socket options handling (getsockopt/setsockopt), BPF sockopt filters, TCP SYN/SYN-ACK option generation, and TCP connection request processing in the core IPv4/TCP networking stack.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "INET", "BPF_SYSCALL" ], "FocusSymbols": [ "do_tcp_setsockopt", "do_tcp_getsockopt", "tcp_conn_request", "tcp_make_synack", "tcp_connect" ], "Reasoning": "The patch introduces TCP_ECN and TCP_ECN_OPTION socket options to allow per-socket configuration and override of the tcp_ecn and tcp_ecn_option sysctl settings. It modifies TCP socket options handling (getsockopt/setsockopt), BPF sockopt filters, TCP SYN/SYN-ACK option generation, and TCP connection request processing in the core IPv4/TCP networking stack.", "WorthFuzzing": true }
23/1	2026/09/10 09:07	action	If	0m Args: { "WorthFuzzing": true } Results: null
24/2	2026/09/10 09:07	agent	kmsan-evaluator	0m Model: core Args: null Results: { "KMSANReasoning": "The patch adds per-socket ECN and AccECN configuration options (TCP_ECN and TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, overriding the global sysctls.\n\nKMSAN applicability analysis:\n- The new fields `ecn_mode` and `ecn_option` in `struct tcp_sock` are explicitly initialized to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` in `tcp_init_sock()` and copied across socket clones.\n- In `do_tcp_getsockopt()`, reading these fields initializes the full `int val` before `copy_to_sockptr()` copies the data to user space. No struct padding or uninitialized stack bytes are exposed to user space.\n- No uninitialized variables, conditional branches on uninitialized memory, or buffer length manipulations that could expose uninitialized memory are introduced.\n\nTherefore, dedicated KMSAN fuzzing is not required as the changes present no uninitialized memory risks.", "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 6304d04c637bcb4a0e424ee4f754d834a3992015 Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 10 09:06:13 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_ecn.h b/include/net/tcp_ecn.h index 865d5c5a7718d..931e0877176c7 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 +31,29 @@ 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 = 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 = tcp_sk(sk)->ecn_option; + + if (opt == TCP_ACCECN_OPTION_UNSPEC) + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option); + return opt; +} + /* 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 +621,7 @@ 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/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/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/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, }, };
25/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 7490 output: 29 thoughts: 821 Thoughts: Analyzing the Patch for KMSAN Implications Okay, let's break this down. My initial thought is to figure out if this patch introduces any uninitialized memory read vulnerabilities that KMSAN might catch. First, I need to understand what this patch actually does. It looks like the core of the patch revolves around adding two new fields, `ecn_mode` and `ecn_option`, both of type `u8`, to the `tcp_sock` structure. These fields are initialized to `TCP_ECN_MODE_UNSPEC` (255) and `TCP_ACCECN_OPTION_UNSPEC` (255) respectively within `tcp_init_sock`. The patch also introduces helper functions, `tcp_ecn_mode_eff(sk)` and `tcp_accecn_option_eff(sk)`. These functions cleverly read the corresponding fields (`tp->ecn_mode` and `tp->ecn_option`). If those fields haven't been explicitly set (i.e., they're still at the UNSPEC value), the helper functions return the sysctl values for ECN mode and ECN option respectively. I see what they're doing here, making the configuration more dynamic at runtime, but I'll make sure it's done safely. Crucially, the patch then replaces direct reads of those sysctl values with calls to these new helper functions within several TCP functions – `tcp_ecn_send_syn`, `tcp_ecn_create_request`, etc. This looks like a refactoring to centralize the ECN logic, but potentially a source of subtle bugs. Then, there are the socket options `TCP_ECN` and `TCP_ECN_OPTION` added to allow userspace control over these settings via `setsockopt` and `getsockopt`. The setsockopt validation checks if the `val` is within a reasonable range, which is good. The implementation uses `WRITE_ONCE` and `READ_ONCE`, which is the right thing to do for ensuring atomicity and visibility between threads. Finally, there is BPF sockopt support added for these new options in `net/core/filter.c`. This part seems straightforward, just checking the size. Now for the real question: are there any uninitialized memory risks? The key is to see where these `ecn_mode` and `ecn_option` fields are initialized and how they are handled throughout the `tcp_sock` lifecycle. I note that `tcp_init_sock` does the initialization. Now, is the `tcp_sock` structure zero-initialized initially, or are there other ways it's created where these fields might not be explicitly set? I need to verify that `tcp_init_sock` is called in every path of creating the TCP socket. The Linux kernel uses `sock_alloc_inode` / `sk_alloc`, which should zero out the memory, and then `tcp_init_sock` sets the fields explicitly. Still, I should confirm. I'm thinking about clone operations, or cases with `accept` or passive opens, or `request_sock`. Are these fields properly initialized when a new socket is created from an existing one? I'm going to look for cloning or copying or re-initialization of the `tcp_sock` structure, especially around functions like `tcp_create_openreq_child`. Time to fire up `grepper` and search for calls to `tcp_init_sock` or mentions of cloning within the relevant files, specifically `net/ipv4/tcp_minisocks.c` and `tcp_ipv4.c`. I need to ensure that every socket creation path properly initializes these new fields to prevent uninitialized reads.
26/3	2026/09/10 09:07	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" }
27/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 9468 output: 32 thoughts: 29 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `tcp_create_openreq_child` Okay, time to dig into the heart of connection establishment. Let's start with `tcp_create_openreq_child`, specifically in `net/ipv4/tcp_minisocks.c`. That's where I'd expect to find the logic for handling a newly arrived connection request, a SYN, that's being spawned from an existing listening socket. I need to refresh my memory on the interactions here, especially around the creation of the child socket. I'll be looking to see how the new socket is initialized with the information from the original request and the parent socket and the memory allocation strategy being used to manage this state. Is it a copy-on-write situation, or are we going for full state duplication at this point? I also want to follow up with any potential locking issues and race conditions that could come into play during the child creation and its addition to the established connection lists. Essentially, I'm checking the handoff of the connection's lifecycle from the listen socket to the newly created child socket. Let's see how well it's done.
28/3	2026/09/10 09:07	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" }
29/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 10597 output: 40 thoughts: 29 Thoughts: Okay, let's dive into this. I'm going to pull up `tcp_create_openreq_child` and take a look at the code within `net/ipv4/tcp_minisocks.c`. I need to refresh my memory on the intricacies of this function, especially within the context of the TCP connection establishment process. I'm particularly interested in how new child sockets are created, and how they relate to the listening socket. I suspect there will be some interesting interplay with the `inet_sock` structure and perhaps some locking primitives too, so I'll be looking out for those. It's time to get into the nitty gritty.
30/3	2026/09/10 09:07	tool	read-file	0m Args: { "File": "net/ipv4/tcp_minisocks.c", "FirstLine": 545, "LineCount": 60 } Results: { "Contents": " 545:\t /\n 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 596:\t\tif (sock_flag(newsk, SOCK_KEEPOPEN))\n 597:\t\t\ttcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));\n 598:\t\n 599:\t\tnewtp-\u003erx_opt.tstamp_ok = ireq-\u003etstamp_ok;\n 600:\t\tnewtp-\u003erx_opt.sack_ok = ireq-\u003esack_ok;\n 601:\t\tnewtp-\u003ewindow_clamp = req-\u003ersk_window_clamp;\n 602:\t\tnewtp-\u003ercv_ssthresh = req-\u003ersk_rcv_wnd;\n 603:\t\tnewtp-\u003ercv_wnd = req-\u003ersk_rcv_wnd;\n 604:\t\tnewtp-\u003ercv_mwnd_seq = newtp-\u003ercv_wup + req-\u003ersk_rcv_wnd;\n" }
31/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11910 output: 32 thoughts: 212 Thoughts: Analyzing TCP ECN Inheritance in Socket Cloning Okay, so I'm looking at how ECN (Explicit Congestion Notification) settings are handled when a new socket is created from a listener socket in the kernel. `inet_csk_clone_lock(sk, req, GFP_ATOMIC)` is the function that does the heavy lifting here. From what I see, it clones `sk` using `sk_clone_lock`, which essentially means a `memcpy` of the entire `struct sock`, including the embedded `struct tcp_sock`, from the listening socket `sk` to the new socket `newsk`. This is important because it tells me that ECN-related fields, specifically `newtp->ecn_mode` and `newtp->ecn_option`, are inherited directly from the listener. That inheritance seems quite direct. Now, my next question is, how are these ECN settings exposed to user space? I need to check how `do_tcp_getsockopt` handles retrieving these values. Let's look at the code: ```c case TCP_ECN: val = READ_ONCE(tp->ecn_mode); break; case TCP_ECN_OPTION: val = READ_ONCE(tp->ecn_option); break; ``` Right, it uses `READ_ONCE` to fetch the values of `tp->ecn_mode` and `tp->ecn_option` from the TCP control block. Seems pretty straightforward, just a direct read of the value. I need to dig deeper into the code around `do_tcp_getsockopt` in `tcp.c` to see how that `val` is then returned to the user. I need to check for any potential issues with synchronization or memory ordering here. I'm especially interested in how that value is transferred to user space, especially in the context of multithreaded access to the socket.
32/3	2026/09/10 09:07	tool	grepper	0m Args: { "Expression": "int do_tcp_getsockopt", "PathPrefix": "net/ipv4" } Results: { "Output": "net/ipv4/tcp.c=4423=struct sk_buff tcp_get_timestamping_opt_stats(const struct sock sk,\n--\nnet/ipv4/tcp.c-4494-\nnet/ipv4/tcp.c:4495:int do_tcp_getsockopt(struct sock *sk, int level,\nnet/ipv4/tcp.c-4496-\t\t int optname, sockptr_t optval, sockptr_t optlen)\n" }
33/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 12707 output: 37 thoughts: 39 Thoughts: Here's my take on the specified sections of `net/ipv4/tcp.c`, considering my expertise: Diving Deep into TCP Congestion Control Alright, let's refresh our understanding of some core TCP functionality. I need to zero in on specific regions within `net/ipv4/tcp.c`, namely lines 4495 to 4520 and then 4840 to 4870. My focus here is likely around congestion control mechanisms. From experience, those line numbers usually touch on key adjustments to the TCP window or retransmission behavior. I'm expecting to find details related to how the kernel responds to packet loss or congestion events. It’s probably related to adjustments to the congestion window, slow start thresholds, or retransmission timeouts. I am especially interested in understanding the interplay of different congestion control algorithms, as the kernel can use several different ones. I'm also ready to analyze the intricate calculations involved in maintaining a good throughput. I may find code related to specific congestion control algorithms, like Cubic or BBR, or possibly the core logic for TCP's congestion avoidance. I'll need to watch for conditional statements, any use of timers and associated context switches, and any use of statistics/counters to fully understand what is going on.
34/3	2026/09/10 09:07	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4495, "LineCount": 40 } Results: { "Contents": "4495:\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)\n4520:\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:\n" }
35/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 13687 output: 37 thoughts: 16 Thoughts: Okay, here's my attempt at summarizing the thought process, as if it were my own, assuming I'm an expert in this field: Diving into `do_tcp_getsockopt` - Let's See What's at the End! Alright, time to get to the heart of the matter. My first instinct is always to jump right to the end of `do_tcp_getsockopt`. I know this function inside and out, but I always find it useful to refresh my memory by quickly reviewing the tail end of things first. It's often where the core logic of the operation and the return path are cleanly laid out. This will give me a quick high-level view of how this function wraps up its work. I want to see how the kernel processes the data and sends it back up to the user-space program that made the call. It gives a good sense of how they actually implement getsockopt.
36/3	2026/09/10 09:07	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 4855, "LineCount": 35 } Results: { "Contents": "4855:\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.\n4880:\t\t /\n4881:\t\tif (level == SOL_TCP \u0026\u0026 optname == TCP_ZEROCOPY_RECEIVE)\n4882:\t\t\treturn true;\n4883:\t\n4884:\t\treturn false;\n4885:\t}\n4886:\t\n4887:\tint tcp_getsockopt(struct sock sk, int level, int optname, char __user optval,\n4888:\t\t\t int __user optlen)\n4889:\t{\n" }
37/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 14462 output: 36 thoughts: 25 Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue: Investigating Potential Filtering Issues Right, let's circle back and take another look at the `sol_tcp_sockopt` handling, specifically within the `net/core/filter.c` context. We've been focusing on the networking stack, and it's always a good practice to revisit these areas, especially when dealing with socket options. Socket options can interact in really subtle ways with filtering mechanisms and it would be a shame to miss something by not looking at this aspect, even if it seems unlikely. Given the nature of this current investigation, it would be prudent to ensure there aren't any potential interactions between those options and any filtering logic that might be at play. We know these areas can get complex quickly, so it's best to be thorough.
38/3	2026/09/10 09:07	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" }
39/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 15337 output: 36 thoughts: 25 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `sol_tcp_sockopt` Alright, let's get down to brass tacks. I need to understand the full context of `sol_tcp_sockopt` and its role within the network filter stack. Specifically, I'm going to navigate to `net/core/filter.c` to examine the rest of the implementation. I'm looking for the meat and potatoes - how this socket option interacts with the filtering logic and any potential gotchas or edge cases that might be relevant to my work. I'm expecting this will illuminate the interaction of the socket option mechanism with the filter subsystem. This is the correct file to understand what is happening under the hood. Time to dig in and see what treasures this section of the kernel holds.
40/3	2026/09/10 09:07	tool	read-file	0m Args: { "File": "net/core/filter.c", "FirstLine": 5700, "LineCount": 25 } 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}\n" }
41/3	2026/09/10 09:07	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 15931 output: 37 thoughts: 157 Thoughts: Analyzing TCP Socket Option Handling Okay, let's break down these socket option functions, specifically focusing on potential uninitialized memory issues. Starting with `do_tcp_getsockopt`, the core concern is how the value (`val`) is handled. It seems pretty straightforward: `val`, an `int`, gets assigned from `tp->ecn_mode`, which is a `u8`. Importantly, this assignment fully initializes all the bits within `val` because of the implicit type promotion. The length check, `len = min_t(unsigned int, len, sizeof(int))`, looks good, ensuring we don't try to copy more data than expected. Finally, the critical `copy_to_sockptr(optval, &val, len)` uses `len` which is bound by `sizeof(int)`, so we're only copying initialized bits of the `int` to userspace. So, `do_tcp_getsockopt` appears safe; no uninitialized data leaks out. Now, let's shift focus to `do_tcp_setsockopt`. We need to examine how `val` is acquired in this context. The prior analysis of `do_tcp_getsockopt` sets the stage for a similar rigorous check in this function.
42/3	2026/09/10 09:08	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 3870, "LineCount": 45 } Results: { "Contents": "3870:\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;\n3880:\t\t\tname[val] = 0;\n3881:\t\n3882:\t\t\tsockopt_lock_sock(sk);\n3883:\t\t\terr = tcp_set_ulp(sk, name);\n3884:\t\t\tsockopt_release_sock(sk);\n3885:\t\t\treturn err;\n3886:\t\t}\n3887:\t\tcase TCP_FASTOPEN_KEY: {\n3888:\t\t\t__u8 key[TCP_FASTOPEN_KEY_BUF_LENGTH];\n3889:\t\t\t__u8 backup_key = NULL;\n3890:\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)))\n" }
43/3	2026/09/10 09:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 17044 output: 249 thoughts: 1150 Thoughts: KMSAN Assessment: TCP ECN Socket Options Alright, let's break this down. My task is to assess whether this patch requires KMSAN (Kernel Memory Sanitizer) or not. First, the patch introduces two new socket options, `TCP_ECN` and `TCP_ECN_OPTION`. These allow for per-socket overrides of the system-wide ECN settings controlled by `sysctl_tcp_ecn` and `sysctl_tcp_ecn_option`, respectively. I see that in `do_tcp_setsockopt`, there's proper type validation, range checks and explicit initialization of the new fields `ecn_mode` and `ecn_option`. I checked that `copy_from_sockptr` is correctly used, ensuring data is copied from user space safely. Next, I need to understand how these new options are used. I identified all uses of `ecn_mode`, `ecn_option`, `tcp_ecn_mode_eff`, and `tcp_accecn_option_eff` within the kernel source. The code seems clean and logically sound, with no obvious issues. I went through all the locations, including `include/net/tcp_ecn.h`, `tcp_ecn_send_syn`, and various parts of `tcp_output.c`. Everything seems to be well-defined and handled in a controlled manner. The crucial part is ensuring no uninitialized memory issues exist. I confirmed that `ecn_mode` and `ecn_option` are properly initialized in `tcp_init_sock()` to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` respectively. `do_tcp_getsockopt` assigns the value to a local `int val` before copying it to userspace, thus eliminating potential issues with uninitialized memory. BPF sockopts are also carefully handled. There's no introduction of any uninitialized memory on the heap, stack, or within any conditional branches. There is no padding concern either. Therefore, given the explicit initialization and controlled data flow, I'm confident that KMSAN isn't needed here. Any concerns with boundary conditions, range limits or other logic errors are issues addressed by KASAN (Kernel Address Sanitizer), LOCKDEP or general code review; these aren't related to uninitialized memory. It's a clean patch that doesn't introduce any new KMSAN concerns. I'll make a note of my reasoning for contrasting KMSAN and KASAN. Let's call `set-results`.
44/3	2026/09/10 09:08	tool	set-results	0m Args: { "KMSANReasoning": "The patch adds per-socket ECN and AccECN configuration options (TCP_ECN and TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, overriding the global sysctls.\n\nKMSAN applicability analysis:\n- The new fields `ecn_mode` and `ecn_option` in `struct tcp_sock` are explicitly initialized to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` in `tcp_init_sock()` and copied across socket clones.\n- In `do_tcp_getsockopt()`, reading these fields initializes the full `int val` before `copy_to_sockptr()` copies the data to user space. No struct padding or uninitialized stack bytes are exposed to user space.\n- No uninitialized variables, conditional branches on uninitialized memory, or buffer length manipulations that could expose uninitialized memory are introduced.\n\nTherefore, dedicated KMSAN fuzzing is not required as the changes present no uninitialized memory risks.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch adds per-socket ECN and AccECN configuration options (TCP_ECN and TCP_ECN_OPTION) via setsockopt/getsockopt and BPF sockops, overriding the global sysctls.\n\nKMSAN applicability analysis:\n- The new fields `ecn_mode` and `ecn_option` in `struct tcp_sock` are explicitly initialized to `TCP_ECN_MODE_UNSPEC` and `TCP_ACCECN_OPTION_UNSPEC` in `tcp_init_sock()` and copied across socket clones.\n- In `do_tcp_getsockopt()`, reading these fields initializes the full `int val` before `copy_to_sockptr()` copies the data to user space. No struct padding or uninitialized stack bytes are exposed to user space.\n- No uninitialized variables, conditional branches on uninitialized memory, or buffer length manipulations that could expose uninitialized memory are introduced.\n\nTherefore, dedicated KMSAN fuzzing is not required as the changes present no uninitialized memory risks.", "NeedsKMSAN": false }

LLM Calls Summary:
Total Calls	Total Tokens	Avg Tokens	Total Duration (Seconds)	Avg Duration (Seconds)

Tool Calls Summary:
Total Calls	Total Duration (Seconds)	Avg Duration (Seconds)