kernel/linux.git/include/net/tcp.h, branch v7.1-rc5

tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction

2026-05-21T02:14:06+00:00

Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming the value would always be consumed by tcp_conn_request() for the same packet that wrote it. That assumption is violated by multiple drop paths between the producer (__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer (tcp_conn_request()): - min_ttl / min_hopcount check - xfrm policy check - tcp_inbound_hash() MD5/AO mismatch - tcp_filter() eBPF/SO_ATTACH_FILTER drop - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv() - tcp_checksum_complete() in tcp_v{4,6}_do_rcv() - tcp_v{4,6}_cookie_check() returning NULL When a packet is dropped on any of these paths, tcp_tw_isn is left set. The next SYN processed on the same CPU then consumes the non zero value in tcp_conn_request(), receiving a potentially predictable ISN. This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu variable. Note that tcp_v{4,6}_fill_cb() do not set it. Very litle impact on overall code size/complexity: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7) Function old new delta tcp_v6_rcv 3038 3042 +4 tcp_v4_rcv 3035 3039 +4 tcp_conn_request 2938 2923 -15 Total: Before=24436060, After=24436053, chg -0.00% Fixes: 41eecbd712b7 ("tcp: replace TCP_SKB_CB(skb)->tcp_tw_isn with a per-cpu field") Reported-by: Chris Mason Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260519084611.2485277-1-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: add data-races annotations around tp->reordering, tp->snd_cwnd

2026-04-18T18:10:12+00:00

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE(), WRITE_ONCE() data_race() annotations to keep KCSAN happy. Fixes: bb7c19f96012 ("tcp: add related fields into SCM_TIMESTAMPING_OPT_STATS") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260416200319.3608680-4-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: annotate data-races in tcp_get_info_chrono_stats()

2026-04-18T18:10:11+00:00

tcp_get_timestamping_opt_stats() does not own the socket lock, this is intentional. It calls tcp_get_info_chrono_stats() while other threads could change chrono fields in tcp_chrono_set(). I do not think we need coherent TCP socket state snapshot in tcp_get_timestamping_opt_stats(), I chose to only add annotations to keep KCSAN happy. Fixes: 1c885808e456 ("tcp: SOF_TIMESTAMPING_OPT_STATS option for SO_TIMESTAMPING") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260416200319.3608680-2-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: update window_clamp when SO_RCVBUF is set

2026-04-13T13:32:35+00:00

Commit under Fixes moved recomputing the window clamp to tcp_measure_rcv_mss() (when scaling_ratio changes). I suspect it missed the fact that we don't recompute the clamp when rcvbuf is set. Until scaling_ratio changes we are stuck with the old window clamp which may be based on the small initial buffer. scaling_ratio may never change. Inspired by Eric's recent commit d1361840f8c5 ("tcp: fix SO_RCVLOWAT and RCVBUF autotuning") plumb the user action thru to TCP and have it update the clamp. A smaller fix would be to just have tcp_rcvbuf_grow() adjust the clamp even if SOCK_RCVBUF_LOCK is set. But IIUC this is what we were trying to get away from in the first place. Fixes: a2cbb1603943 ("tcp: Update window clamping condition") Signed-off-by: Jakub Kicinski Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260408001438.129165-1-kuba@kernel.org Signed-off-by: Paolo Abeni

Merge branch 'net-reduce-sk_filter-and-friends-bloat'

2026-04-12T21:30:28+00:00

Eric Dumazet says: ==================== net: reduce sk_filter() (and friends) bloat Some functions return an error by value, and a drop_reason by an output parameter. This extra parameter can force stack canaries. A drop_reason is enough and more efficient. This series reduces bloat by 678 bytes on x86_64: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.final add/remove: 0/0 grow/shrink: 3/18 up/down: 79/-757 (-678) Function old new delta vsock_queue_rcv_skb 50 79 +29 ipmr_cache_report 1290 1315 +25 ip6mr_cache_report 1322 1347 +25 tcp_v6_rcv 3169 3167 -2 packet_rcv_spkt 329 327 -2 unix_dgram_sendmsg 1731 1726 -5 netlink_unicast 957 945 -12 netlink_dump 1372 1359 -13 sk_filter_trim_cap 889 858 -31 netlink_broadcast_filtered 1633 1595 -38 tcp_v4_rcv 3152 3111 -41 raw_rcv_skb 122 80 -42 ping_queue_rcv_skb 109 61 -48 ping_rcv 215 162 -53 rawv6_rcv_skb 278 224 -54 __sk_receive_skb 690 632 -58 raw_rcv 591 527 -64 udpv6_queue_rcv_one_skb 935 869 -66 udp_queue_rcv_one_skb 919 853 -66 tun_net_xmit 1146 1074 -72 sock_queue_rcv_skb_reason 166 76 -90 Total: Before=29722890, After=29722212, chg -0.00% Future conversions from sock_queue_rcv_skb() to sock_queue_rcv_skb_reason() can be done later. ==================== Link: https://patch.msgid.link/20260409145625.2306224-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net: change sk_filter_trim_cap() to return a drop_reason by value

2026-04-12T21:30:25+00:00

Current return value can be replaced with the drop_reason, reducing kernel bloat: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/2 grow/shrink: 1/11 up/down: 32/-603 (-571) Function old new delta tcp_v6_rcv 3135 3167 +32 unix_dgram_sendmsg 1731 1726 -5 netlink_unicast 957 945 -12 netlink_dump 1372 1359 -13 sk_filter_trim_cap 882 858 -24 tcp_v4_rcv 3143 3111 -32 __pfx_tcp_filter 32 - -32 netlink_broadcast_filtered 1633 1595 -38 sock_queue_rcv_skb_reason 126 76 -50 tun_net_xmit 1127 1074 -53 __sk_receive_skb 690 632 -58 udpv6_queue_rcv_one_skb 935 869 -66 udp_queue_rcv_one_skb 919 853 -66 tcp_filter 154 - -154 Total: Before=29722783, After=29722212, chg -0.00% Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260409145625.2306224-6-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: change tcp_filter() to return the reason by value

2026-04-12T21:30:25+00:00

sk_filter_trim_cap() will soon return the reason by value, do the same for tcp_filter(). Note: tcp_filter() is no longer inlined. Following patch will inline it again. $ scripts/bloat-o-meter -t vmlinux.4 vmlinux.5 add/remove: 2/0 grow/shrink: 0/2 up/down: 186/-43 (143) Function old new delta tcp_filter - 154 +154 __pfx_tcp_filter - 32 +32 tcp_v4_rcv 3152 3143 -9 tcp_v6_rcv 3169 3135 -34 Total: Before=29722640, After=29722783, chg +0.00% Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260409145625.2306224-5-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: add indirect call wrapper in tcp_conn_request()

2026-04-12T16:17:03+00:00

Small improvement in SYN processing, to directly call tcp_v6_init_seq_and_ts_off() or tcp_v4_init_seq_and_ts_off(). Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260410174950.745670-1-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: return a drop_reason from tcp_add_backlog()

2026-04-12T16:07:53+00:00

Part of a stack canary removal from tcp_v{4,6}_rcv(). Return a drop_reason instead of a boolean, so that we no longer have to pass the address of a local variable. $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-37 (-37) Function old new delta tcp_v6_rcv 3133 3129 -4 tcp_v4_rcv 3206 3202 -4 tcp_add_backlog 1281 1252 -29 Total: Before=25567186, After=25567149, chg -0.00% Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260409101147.1642967-1-edumazet@google.com Signed-off-by: Jakub Kicinski

tcp: add recv_should_stop helper

2026-04-07T02:14:27+00:00

Factor out a new helper tcp_recv_should_stop() from tcp_recvmsg_locked() and tcp_splice_read() to check whether to stop receiving. And use this helper in mptcp_recvmsg() and mptcp_splice_read() to reduce redundant code. Suggested-by: Paolo Abeni Acked-by: Mat Martineau Signed-off-by: Geliang Tang Acked-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260403-net-next-mptcp-msg_eor-misc-v1-3-b0b33bea3fed@kernel.org Signed-off-by: Jakub Kicinski