This is a note to let you know that I've just added the patch titled
net: Remove acked SYN flag from packet in the transmit queue correctly
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-remove-acked-syn-flag-from-packet-in-the-transmi.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 001762d3a8336588d37d5121c56e3552b66f8443
Author: Dong Chenchen <dongchenchen2@xxxxxxxxxx>
Date: Sun Dec 10 10:02:00 2023 +0800
net: Remove acked SYN flag from packet in the transmit queue correctly
[ Upstream commit f99cd56230f56c8b6b33713c5be4da5d6766be1f ]
syzkaller report:
kernel BUG at net/core/skbuff.c:3452!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.7.0-rc4-00009-gbee0e7762ad2-dirty #135
RIP: 0010:skb_copy_and_csum_bits (net/core/skbuff.c:3452)
Call Trace:
icmp_glue_bits (net/ipv4/icmp.c:357)
__ip_append_data.isra.0 (net/ipv4/ip_output.c:1165)
ip_append_data (net/ipv4/ip_output.c:1362 net/ipv4/ip_output.c:1341)
icmp_push_reply (net/ipv4/icmp.c:370)
__icmp_send (./include/net/route.h:252 net/ipv4/icmp.c:772)
ip_fragment.constprop.0 (./include/linux/skbuff.h:1234 net/ipv4/ip_output.c:592 net/ipv4/ip_output.c:577)
__ip_finish_output (net/ipv4/ip_output.c:311 net/ipv4/ip_output.c:295)
ip_output (net/ipv4/ip_output.c:427)
__ip_queue_xmit (net/ipv4/ip_output.c:535)
__tcp_transmit_skb (net/ipv4/tcp_output.c:1462)
__tcp_retransmit_skb (net/ipv4/tcp_output.c:3387)
tcp_retransmit_skb (net/ipv4/tcp_output.c:3404)
tcp_retransmit_timer (net/ipv4/tcp_timer.c:604)
tcp_write_timer (./include/linux/spinlock.h:391 net/ipv4/tcp_timer.c:716)
The panic issue was trigered by tcp simultaneous initiation.
The initiation process is as follows:
TCP A TCP B
1. CLOSED CLOSED
2. SYN-SENT --> <SEQ=100><CTL=SYN> ...
3. SYN-RECEIVED <-- <SEQ=300><CTL=SYN> <-- SYN-SENT
4. ... <SEQ=100><CTL=SYN> --> SYN-RECEIVED
5. SYN-RECEIVED --> <SEQ=100><ACK=301><CTL=SYN,ACK> ...
// TCP B: not send challenge ack for ack limit or packet loss
// TCP A: close
tcp_close
tcp_send_fin
if (!tskb && tcp_under_memory_pressure(sk))
tskb = skb_rb_last(&sk->tcp_rtx_queue); //pick SYN_ACK packet
TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN; // set FIN flag
6. FIN_WAIT_1 --> <SEQ=100><ACK=301><END_SEQ=102><CTL=SYN,FIN,ACK> ...
// TCP B: send challenge ack to SYN_FIN_ACK
7. ... <SEQ=301><ACK=101><CTL=ACK> <-- SYN-RECEIVED //challenge ack
// TCP A: <SND.UNA=101>
8. FIN_WAIT_1 --> <SEQ=101><ACK=301><END_SEQ=102><CTL=SYN,FIN,ACK> ... // retransmit panic
__tcp_retransmit_skb //skb->len=0
tcp_trim_head
len = tp->snd_una - TCP_SKB_CB(skb)->seq // len=101-100
__pskb_trim_head
skb->data_len -= len // skb->len=-1, wrap around
... ...
ip_fragment
icmp_glue_bits //BUG_ON
If we use tcp_trim_head() to remove acked SYN from packet that contains data
or other flags, skb->len will be incorrectly decremented. We can remove SYN
flag that has been acked from rtx_queue earlier than tcp_trim_head(), which
can fix the problem mentioned above.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Co-developed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Dong Chenchen <dongchenchen2@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231210020200.1539875-1-dongchenchen2@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a0875dc60e08f..670804d4c1690 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2890,7 +2890,13 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
if (skb_still_in_host_queue(sk, skb))
return -EBUSY;
+start:
if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
+ if (unlikely(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
+ TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
+ TCP_SKB_CB(skb)->seq++;
+ goto start;
+ }
if (unlikely(before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))) {
WARN_ON_ONCE(1);
return -EINVAL;
