CVE-2026-43029: mptcp: fix soft lockup in mptcp_recvmsg()
In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix soft lockup in mptcprecvmsg()
syzbot reported a soft lockup in mptcprecvmsg() [0].
When receiving data with MSGPEEK | MSGWAITALL flags, the skb is not removed from the skreceivequeue. This causes skwaitdata() 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 skwaitdata() to make informed waiting decisions and prevent infinite loops when MSGPEEK 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:skwaitdata+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> mptcprecvmsg+0x547/0x8c0 net/mptcp/protocol.c:2329 inetrecvmsg+0x11f/0x130 net/ipv4/afinet.c:891 sockrecvmsg+0x94/0xc0 net/socket.c:1100 sysrecvfrom+0xb2/0x130 net/socket.c:2256 x64sysrecvfrom+0x1f/0x30 net/socket.c:2267 dosyscall64+0x59/0x2d0 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x76/0x7e arch/x86/entry/entry64.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 ORIGRAX: 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>
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-43029?
CVE-2026-43029 is categorized as a moderate severity vulnerability due to the potential for causing a soft lockup within the Linux kernel.
How does CVE-2026-43029 affect the Linux kernel?
CVE-2026-43029 affects the Linux kernel by causing a soft lockup in the mptcp_recvmsg() function when using specific message flags.
How can I protect my system from CVE-2026-43029?
To protect your system from CVE-2026-43029, ensure that your Linux kernel is updated to the latest stable version where this vulnerability has been addressed.
What is the fixed version for CVE-2026-43029?
The fixed version for CVE-2026-43029 is included in the latest stable releases of the Linux kernel following the patches provided.
Are there any known exploitations of CVE-2026-43029?
As of now, there are no publicly known exploitations of CVE-2026-43029 reported.