Patch "mptcp: fix soft lockup in mptcp_recvmsg()" has been added to the 6.12-stable tree

gregkh
2026-04-13T11:52:37Z

This is a note to let you know that I've just added the patch titled

mptcp: fix soft lockup in mptcp_recvmsg()

to the 6.12-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-fix-soft-lockup-in-mptcp_recvmsg.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.

From matttbe@kernel.org Thu Apr 9 13:45:18 2026
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Thu, 9 Apr 2026 13:44:40 +0200
Subject: mptcp: fix soft lockup in mptcp_recvmsg()
To: stable@vger.kernel.org, gregkh@linuxfoundation.org, sashal@kernel.org
Cc: MPTCP Upstream <mptcp@lists.linux.dev>, Li Xiasong <lixiasong1@huawei.com>, "Matthieu Baerts (NGI0)" <matttbe@kernel.org>, Jakub Kicinski <kuba@kernel.org>
Message-ID: <20260409114439.1158386-2-matttbe@kernel.org>

From: Li Xiasong <lixiasong1@huawei.com>

commit 5dd8025a49c268ab6b94d978532af3ad341132a7 upstream.

syzbot reported a soft lockup in mptcp_recvmsg() [0].

When receiving data with MSG_PEEK | MSG_WAITALL flags, the skb is not
removed from the sk_receive_queue. This causes sk_wait_data() to always
find available data and never perform actual waiting, leading to a soft
lockup.

Fix this by adding a 'last' parameter to track the last peeked skb.
This allows sk_wait_data() to make informed waiting decisions and prevent
infinite loops when MSG_PEEK is used.

[0]:
watchdog: BUG: soft lockup - CPU#2 stuck for 156s! [server:1963]
Modules linked in:
CPU: 2 UID: 0 PID: 1963 Comm: server Not tainted 6.19.0-rc8 #61 PREEMPT(none)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:sk_wait_data+0x15/0x190
Code: 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 41 56 41 55 41 54 49 89 f4 55 48 89 d5 53 48 89 fb <48> 83 ec 30 65 48 8b 05 17 a4 6b 01 48 89 44 24 28 31 c0 65 48 8b
RSP: 0018:ffffc90000603ca0 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff888102bf0800 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffc90000603d18 RDI: ffff888102bf0800
RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000000101
R10: 0000000000000000 R11: 0000000000000075 R12: ffffc90000603d18
R13: ffff888102bf0800 R14: ffff888102bf0800 R15: 0000000000000000
FS: 00007f6e38b8c4c0(0000) GS:ffff8881b877e000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055aa7bff1680 CR3: 0000000105cbe000 CR4: 00000000000006f0
Call Trace:
<TASK>
mptcp_recvmsg+0x547/0x8c0 net/mptcp/protocol.c:2329
inet_recvmsg+0x11f/0x130 net/ipv4/af_inet.c:891
sock_recvmsg+0x94/0xc0 net/socket.c:1100
__sys_recvfrom+0xb2/0x130 net/socket.c:2256
__x64_sys_recvfrom+0x1f/0x30 net/socket.c:2267
do_syscall_64+0x59/0x2d0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x76/0x7e arch/x86/entry/entry_64.S:131
RIP: 0033:0x7f6e386a4a1d
Code: 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8d 05 f1 de 2c 00 41 89 ca 8b 00 85 c0 75 20 45 31 c9 45 31 c0 b8 2d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 6b f3 c3 66 0f 1f 84 00 00 00 00 00 41 56 41
RSP: 002b:00007ffc3c4bb078 EFLAGS: 00000246 ORIG_RAX: 000000000000002d
RAX: ffffffffffffffda RBX: 000000000000861e RCX: 00007f6e386a4a1d
RDX: 00000000000003ff RSI: 00007ffc3c4bb150 RDI: 0000000000000004
RBP: 00007ffc3c4bb570 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000103 R11: 0000000000000246 R12: 00005605dbc00be0
R13: 00007ffc3c4bb650 R14: 0000000000000000 R15: 0000000000000000
</TASK>

Fixes: 8e04ce45a8db ("mptcp: fix MSG_PEEK stream corruption")
Signed-off-by: Li Xiasong <lixiasong1@huawei.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260330120335.659027-1-lixiasong1@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in protocol.c, because commit bc68b0efa1bf ("mptcp: move the
whole rx path under msk socket lock protection") and commit
d88b2127b242 ("mptcp: add eat_recv_skb helper") (with some
dependences) are not in this version. These conflicts were in the
context, and not related to this fix. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/protocol.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1997,7 +1997,7 @@ static int __mptcp_recvmsg_mskq(struct m
struct msghdr *msg,
size_t len, int flags, int copied_total,
struct scm_timestamping_internal *tss,
- int *cmsg_flags)
+ int *cmsg_flags, struct sk_buff **last)
{
struct sk_buff *skb, *tmp;
int total_data_len = 0;
@@ -2013,6 +2013,7 @@ static int __mptcp_recvmsg_mskq(struct m
/* skip already peeked skbs */
if (total_data_len + data_len <= copied_total) {
total_data_len += data_len;
+ *last = skb;
continue;
}

@@ -2053,6 +2054,8 @@ static int __mptcp_recvmsg_mskq(struct m
WRITE_ONCE(msk->rmem_released, msk->rmem_released + skb->truesize);
__skb_unlink(skb, &msk->receive_queue);
__kfree_skb(skb);
+ } else {
+ *last = skb;
}

if (copied >= len)
@@ -2274,10 +2277,12 @@ static int mptcp_recvmsg(struct sock *sk
cmsg_flags = MPTCP_CMSG_INQ;

while (copied < len) {
+ struct sk_buff *last = NULL;
int err, bytes_read;

bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied, flags,
- copied, &tss, &cmsg_flags);
+ copied, &tss, &cmsg_flags,
+ &last);
if (unlikely(bytes_read < 0)) {
if (!copied)
copied = bytes_read;
@@ -2335,7 +2340,7 @@ static int mptcp_recvmsg(struct sock *sk

pr_debug("block timeout %ld\n", timeo);
mptcp_cleanup_rbuf(msk, copied);
- err = sk_wait_data(sk, &timeo, NULL);
+ err = sk_wait_data(sk, &timeo, last);
if (err < 0) {
err = copied ? : err;
goto out_err;

Patches currently in stable-queue which might be from matttbe@kernel.org are

queue-6.12/mptcp-fix-slab-use-after-free-in-__inet_lookup_established.patch
queue-6.12/revert-mptcp-add-needs_id-for-netlink-appending-addr.patch
queue-6.12/mptcp-fix-soft-lockup-in-mptcp_recvmsg.patch