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: 41eecbd712 ("tcp: replace TCP_SKB_CB(skb)->tcp_tw_isn with a per-cpu field")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260519084611.2485277-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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: 1c885808e4 ("tcp: SOF_TIMESTAMPING_OPT_STATS option for SO_TIMESTAMPING")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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 d1361840f8 ("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: a2cbb16039 ("tcp: Update window clamping condition")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumaze@google.com>
Link: https://patch.msgid.link/20260408001438.129165-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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 <edumazet@google.com>
Link: https://patch.msgid.link/20260409145625.2306224-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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 <edumazet@google.com>
Link: https://patch.msgid.link/20260409101147.1642967-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(tcp_congestion_ops)->cwnd_event() is called very often, with
@event oscillating between CA_EVENT_TX_START and other values.
This is not branch prediction friendly.
Provide a new cwnd_event_tx_start pointer dedicated for CA_EVENT_TX_START.
Both BBR and CUBIC benefit from this change, since they only care
about CA_EVENT_TX_START.
No change in kernel size:
$ scripts/bloat-o-meter -t vmlinux.0 vmlinux
add/remove: 4/4 grow/shrink: 3/1 up/down: 564/-568 (-4)
Function old new delta
bbr_cwnd_event_tx_start - 450 +450
cubictcp_cwnd_event_tx_start - 70 +70
__pfx_cubictcp_cwnd_event_tx_start - 16 +16
__pfx_bbr_cwnd_event_tx_start - 16 +16
tcp_unregister_congestion_control 93 99 +6
tcp_update_congestion_control 518 521 +3
tcp_register_congestion_control 422 425 +3
__tcp_transmit_skb 3308 3306 -2
__pfx_cubictcp_cwnd_event 16 - -16
__pfx_bbr_cwnd_event 16 - -16
cubictcp_cwnd_event 80 - -80
bbr_cwnd_event 454 - -454
Total: Before=25240512, After=25240508, chg -0.00%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260323234920.1097858-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
By default, the Linux TCP implementation does not shrink the
advertised window (RFC 7323 calls this "window retraction") with the
following exceptions:
- When an incoming segment cannot be added due to the receive buffer
running out of memory. Since commit 8c670bdfa5 ("tcp: correct
handling of extreme memory squeeze") a zero window will be
advertised in this case. It turns out that reaching the required
memory pressure is easy when window scaling is in use. In the
simplest case, sending a sufficient number of segments smaller than
the scale factor to a receiver that does not read data is enough.
- Commit b650d953cd ("tcp: enforce receive buffer memory limits by
allowing the tcp window to shrink") addressed the "eating memory"
problem by introducing a sysctl knob that allows shrinking the
window before running out of memory.
However, RFC 7323 does not only state that shrinking the window is
necessary in some cases, it also formulates requirements for TCP
implementations when doing so (Section 2.4).
This commit addresses the receiver-side requirements: After retracting
the window, the peer may have a snd_nxt that lies within a previously
advertised window but is now beyond the retracted window. This means
that all incoming segments (including pure ACKs) will be rejected
until the application happens to read enough data to let the peer's
snd_nxt be in window again (which may be never).
To comply with RFC 7323, the receiver MUST honor any segment that
would have been in window for any ACK sent by the receiver and, when
window scaling is in effect, SHOULD track the maximum window sequence
number it has advertised. This patch tracks that maximum window
sequence number rcv_mwnd_seq throughout the connection and uses it in
tcp_sequence() when deciding whether a segment is acceptable.
rcv_mwnd_seq is updated together with rcv_wup and rcv_wnd in
tcp_select_window(). If we count tcp_sequence() as fast path, it is
read in the fast path. Therefore, rcv_mwnd_seq is put into rcv_wnd's
cacheline group.
The logic for handling received data in tcp_data_queue() is already
sufficient and does not need to be updated.
Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-1-4c7f96b1ec69@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Majority of tcp_release_cb() calls do nothing at all.
Provide tcp_release_cb_cond() helper so that release_sock()
can avoid these calls.
Also hint the compiler that __release_sock() and wake_up()
are rarely called.
$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-77 (-77)
Function old new delta
release_sock 258 181 -77
Total: Before=25235790, After=25235713, chg -0.00%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260310124451.2280968-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
tcp_chrono_start() is small enough, and used in TCP sendmsg()
fast path (from tcp_skb_entail()).
Note clang is already inlining it from functions in tcp_output.c.
Inlining it improves performance and reduces bloat :
$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/2 grow/shrink: 1/0 up/down: 1/-84 (-83)
Function old new delta
tcp_skb_entail 280 281 +1
__pfx_tcp_chrono_start 16 - -16
tcp_chrono_start 68 - -68
Total: Before=25192434, After=25192351, chg -0.00%
Note that tcp_chrono_stop() is too big.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20260308123549.2924460-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Cross-merge networking fixes after downstream PR (net-7.0-rc3).
No conflicts.
Adjacent changes:
net/netfilter/nft_set_rbtree.c
fb7fb40163 ("netfilter: nf_tables: clone set on flush only")
3aea466a43 ("netfilter: nft_set_rbtree: don't disable bh when acquiring tree lock")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Instead of using struct timespec64 in scm_timestamping_internal,
use ktime_t, saving 24 bytes in kernel stack.
This makes tcp_update_recv_tstamps() small enough to be inlined.
The ktime_t -> timespec64 conversions happen after socket lock
has been released in tcp_recvmsg(), and only if the application
requested them.
$ scripts/bloat-o-meter -t vmlinux.0 vmlinux
add/remove: 0/2 grow/shrink: 5/4 up/down: 146/-277 (-131)
Function old new delta
tcp_zerocopy_receive 2383 2425 +42
mptcp_recvmsg 1565 1607 +42
tcp_recvmsg_locked 3797 3823 +26
put_cmsg_scm_timestamping64 131 149 +18
put_cmsg_scm_timestamping 131 149 +18
__pfx_tcp_update_recv_tstamps 16 - -16
do_tcp_getsockopt 4024 4006 -18
tcp_recv_timestamp 474 430 -44
tcp_zc_handle_leftover 417 371 -46
__sock_recv_timestamp 1087 1031 -56
tcp_update_recv_tstamps 97 - -97
Total: Before=25223788, After=25223657, chg -0.00%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20260304012747.881644-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This reverts 28ee1b746f ("secure_seq: downgrade to per-host timestamp offsets")
tcp_tw_recycle went away in 2017.
Zhouyan Deng reported off-path TCP source port leakage via
SYN cookie side-channel that can be fixed in multiple ways.
One of them is to bring back TCP ports in TS offset randomization.
As a bonus, we perform a single siphash() computation
to provide both an ISN and a TS offset.
Fixes: 28ee1b746f ("secure_seq: downgrade to per-host timestamp offsets")
Reported-by: Zhouyan Deng <dengzhouyan_nwpu@163.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Acked-by: Florian Westphal <fw@strlen.de>
Link: https://patch.msgid.link/20260302205527.1982836-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Cross-merge networking fixes after downstream PR (net-7.0-rc2).
Conflicts:
tools/testing/selftests/drivers/net/hw/rss_ctx.py
19c3a2a81d ("selftests: drv-net: rss: Generate unique ports for RSS context tests")
ce5a0f4612 ("selftests: drv-net: rss_ctx: test RSS contexts persist after ifdown/up")
include/net/inet_connection_sock.h
858d2a4f67 ("tcp: fix potential race in tcp_v6_syn_recv_sock()")
fcd3d039fa ("tcp: make tcp_v{4,6}_send_check() static")
https://lore.kernel.org/aZ8PSFLzBrEU3I89@sirena.org.uk
drivers/net/ethernet/mellanox/mlx5/core/en/xsk/setup.c
drivers/net/ethernet/mellanox/mlx5/core/en/xsk/pool.c
69050f8d6d ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types")
bf4afc53b7 ("Convert 'alloc_obj' family to use the new default GFP_KERNEL argument")
8a96b9144f ("net/mlx5e: Alloc xsk channel param out of mlx5e_open_xsk()")
Adjacent changes:
net/netfilter/ipvs/ip_vs_ctl.c
c59bd9e62e ("ipvs: use more counters to avoid service lookups")
bf4afc53b7 ("Convert 'alloc_obj' family to use the new default GFP_KERNEL argument")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
tcp_v{4,6}_send_check() are only called from tcp_output.c
and should be made static so that the compiler does not need
to put an out of line copy of them.
Remove (struct inet_connection_sock_af_ops) send_check field
and use instead @net_header_len.
Move @net_header_len close to @queue_xmit for data locality
as both are used in TCP tx fast path.
$ scripts/bloat-o-meter -t vmlinux.2 vmlinux.3
add/remove: 0/2 grow/shrink: 0/3 up/down: 0/-172 (-172)
Function old new delta
__tcp_transmit_skb 3426 3423 -3
tcp_v4_send_check 136 132 -4
mptcp_subflow_init 777 763 -14
__pfx_tcp_v6_send_check 16 - -16
tcp_v6_send_check 135 - -135
Total: Before=25143196, After=25143024, chg -0.00%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260223100729.3761597-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Inline __tcp_v4_send_check(), like __tcp_v6_send_check().
Move tcp_v4_send_check() to tcp_output.c close to
its fast path caller (__tcp_transmit_skb()).
Note __tcp_v4_send_check() is still out-of-line for tcp4_gso_segment()
because it is called in an unlikely() section.
$ scripts/bloat-o-meter -t vmlinux.0 vmlinux.1
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-9 (-9)
Function old new delta
__tcp_v4_send_check 130 121 -9
Total: Before=25143100, After=25143091, chg -0.00%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260223100729.3761597-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Eric Dumazet
Jakub Kicinski
Geliang Tang
Jiayuan Chen
Simon Baatz