diff options
| author | Yilin Zhang <yilinzhang@moonshot.ai> | 2026-09-24 12:49:00 +0800 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-09-24 09:17:10 -0700 |
| commit | fe99bbeee5c5dbd3abc30721a8079ced59649d97 (patch) | |
| tree | a983718e1dd5f2de4f05cfc58217735bea003abf /net/ipv4 | |
| parent | 26cc0e69cce062cd3aa6fae33074684669c35a71 (diff) | |
tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()
When tcp_send_synack() replaces the cloned SYN skb at the head of the
retransmit queue with a copy, it frees the original with
tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack.
tp->retransmit_skb_hint keeps pointing at the freed
skbuff_fclone_cache object.
The dangling hint is read in tcp_verify_retransmit_hint() and used as
the root of the rbtree walk in tcp_xmit_retransmit_queue(). An
unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with
an attacker-supplied ICMP fragmentation-needed message, after which a
simultaneous open frees the armed SYN skb:
BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)
Read of size 4 at addr ffff88800604d928 by task swapper/1/0
Call Trace:
tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)
tcp_simple_retransmit (net/ipv4/tcp_input.c:3158)
tcp_v4_err (net/ipv4/tcp_ipv4.c:587)
Sync the hint to the copy.
Fixes: c31b70c9968f ("tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit")
Reported-by: Kimi Security Team <bug-report@moonshot.ai>
Tested-by: Weiming Shi <shiweiming@moonshot.ai>
Signed-off-by: Yilin Zhang <yilinzhang@moonshot.ai>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/8a9dff4063a2745653b7e88ceb745d75efa16e68.1790224474.git.yilinzhang@moonshot.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/tcp_output.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d960e3de7d50..e0c392e29de5 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3886,6 +3886,7 @@ void tcp_send_active_reset(struct sock *sk, enum sk_rst_reason reason) */ int tcp_send_synack(struct sock *sk) { + struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; skb = tcp_rtx_queue_head(sk); @@ -3903,6 +3904,8 @@ int tcp_send_synack(struct sock *sk) if (!nskb) return -ENOMEM; INIT_LIST_HEAD(&nskb->tcp_tsorted_anchor); + if (skb == tp->retransmit_skb_hint) + tp->retransmit_skb_hint = nskb; tcp_highest_sack_replace(sk, skb, nskb); tcp_rtx_queue_unlink_and_free(skb, sk); __skb_header_release(nskb); |