This is a note to let you know that I've just added the patch titled
mptcp: more conservative check for zero probes
to the 5.15-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:
mptcp-more-conservative-check-for-zero-probes.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 141c3465d213aff03d860801c1823cc610b5741e
Author: Paolo Abeni <pabeni@xxxxxxxxxx>
Date: Wed Oct 18 11:23:54 2023 -0700
mptcp: more conservative check for zero probes
[ Upstream commit 72377ab2d671befd6390a1d5677f5cca61235b65 ]
Christoph reported that the MPTCP protocol can find the subflow-level
write queue unexpectedly not empty while crafting a zero-window probe,
hitting a warning:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 188 at net/mptcp/protocol.c:1312 mptcp_sendmsg_frag+0xc06/0xe70
Modules linked in:
CPU: 0 PID: 188 Comm: kworker/0:2 Not tainted 6.6.0-rc2-g1176aa719d7a #47
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
Workqueue: events mptcp_worker
RIP: 0010:mptcp_sendmsg_frag+0xc06/0xe70 net/mptcp/protocol.c:1312
RAX: 47d0530de347ff6a RBX: 47d0530de347ff6b RCX: ffff8881015d3c00
RDX: ffff8881015d3c00 RSI: 47d0530de347ff6b RDI: 47d0530de347ff6b
RBP: 47d0530de347ff6b R08: ffffffff8243c6a8 R09: ffffffff82042d9c
R10: 0000000000000002 R11: ffffffff82056850 R12: ffff88812a13d580
R13: 0000000000000001 R14: ffff88812b375e50 R15: ffff88812bbf3200
FS: 0000000000000000(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000695118 CR3: 0000000115dfc001 CR4: 0000000000170ef0
Call Trace:
<TASK>
__subflow_push_pending+0xa4/0x420 net/mptcp/protocol.c:1545
__mptcp_push_pending+0x128/0x3b0 net/mptcp/protocol.c:1614
mptcp_release_cb+0x218/0x5b0 net/mptcp/protocol.c:3391
release_sock+0xf6/0x100 net/core/sock.c:3521
mptcp_worker+0x6e8/0x8f0 net/mptcp/protocol.c:2746
process_scheduled_works+0x341/0x690 kernel/workqueue.c:2630
worker_thread+0x3a7/0x610 kernel/workqueue.c:2784
kthread+0x143/0x180 kernel/kthread.c:388
ret_from_fork+0x4d/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:304
</TASK>
The root cause of the issue is that expectations are wrong: e.g. due
to MPTCP-level re-injection we can hit the critical condition.
Explicitly avoid the zero-window probe when the subflow write queue
is not empty and drop the related warnings.
Reported-by: Christoph Paasch <cpaasch@xxxxxxxxx>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/444
Fixes: f70cad1085d1 ("mptcp: stop relying on tcp_tx_skb_cache")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Mat Martineau <martineau@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231018-send-net-20231018-v1-3-17ecb002e41d@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index b9613e02e2de1..62e1875b92904 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1337,7 +1337,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
if (copy == 0) {
u64 snd_una = READ_ONCE(msk->snd_una);
- if (snd_una != msk->snd_nxt) {
+ if (snd_una != msk->snd_nxt || tcp_write_queue_tail(ssk)) {
tcp_remove_empty_skb(ssk);
return 0;
}
@@ -1345,11 +1345,6 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
zero_window_probe = true;
data_seq = snd_una - 1;
copy = 1;
-
- /* all mptcp-level data is acked, no skbs should be present into the
- * ssk write queue
- */
- WARN_ON_ONCE(reuse_skb);
}
copy = min_t(size_t, copy, info->limit - info->sent);
@@ -1379,7 +1374,6 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
if (reuse_skb) {
TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
mpext->data_len += copy;
- WARN_ON_ONCE(zero_window_probe);
goto out;
}
