diff options
| author | Jiayuan Chen <jiayuan.chen@linux.dev> | 2026-08-26 22:11:26 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-09-14 13:20:53 +0200 |
| commit | 711bfd762bec05fb19bc3b17cbb157c39f4e66da (patch) | |
| tree | 66f56699395c5f8d62c6393d7257ef6960385cd7 | |
| parent | 561cbd6d49022c9a383e22a39c87a165a4d39f9c (diff) | |
tcp: fix corruption of urgent data on multi-segment retransmit
[ Upstream commit ce2b807f42ed5e55567b8864ab72963f90779270 ]
On the normal xmit path, while in urgent mode we refuse to build a
multi-segment TSO packet, so every segment gets its own urg_ptr:
/* tcp_write_xmit() */
limit = mss_now;
if (tso_segs > 1 && !tcp_urg_mode(tp))
limit = tcp_mss_split_point(...);
The retransmit path has no such guard. __tcp_retransmit_skb() builds a
segs > 1 skb and hands it to the GSO layer, which only advances th->seq
per segment and copies urg_ptr verbatim:
/* __tcp_retransmit_skb() */
len = cur_mss * segs; /* segs > 1, no urg_mode check */
...
/* tcp_gso_segment(): bumps seq only, urg_ptr is copied */
urg_ptr is an offset from the segment's own seq, so a copied value points
at a different place on each segment. The receiver rebuilds the absolute
urgent seq as seg.seq + urg_ptr, so it walks a moving urgent point instead
of the one OOB byte:
seg1 seq 1 urg_ptr 5001 -> urgent @ 5001 (ok)
seg2 seq 1001 urg_ptr 5001 -> urgent @ 6001 (wrong, +MSS)
seg3 seq 2001 urg_ptr 5001 -> urgent @ 7001 (wrong, +2*MSS)
The real OOB byte is never pointed at, so the receiver stops splicing it
out and delivers it as normal in-band data, corrupting the stream.
Guard the retransmit length like the xmit path: keep segs = 1 while in
urgent mode.
Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260826141145.67823-1-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | net/ipv4/tcp_output.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index a2d5e9f1fe24..d730a3709f85 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3216,7 +3216,7 @@ start: avail_wnd = cur_mss; } - len = cur_mss * segs; + len = cur_mss * (tcp_urg_mode(tp) ? 1 : segs); if (len > avail_wnd) { len = rounddown(avail_wnd, cur_mss); if (!len) |