Commit ce2b807f42ed for kernel

commit ce2b807f42ed5e55567b8864ab72963f90779270
Author: Jiayuan Chen <jiayuan.chen@linux.dev>
Date:   Wed Aug 26 22:11:26 2026 +0800

    tcp: fix corruption of urgent data on multi-segment retransmit

    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>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f2709d585edb..6f4dca4a4de9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3603,7 +3603,7 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 		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)