CVE-2026-23321: mptcp: pm: in-kernel: always mark signal+subflow endp as used
In the Linux kernel, the following vulnerability has been resolved:
mptcp: pm: in-kernel: always mark signal+subflow endp as used
Syzkaller managed to find a combination of actions that was generating this warning:
msk->pm.localaddrused == 0 WARNING: net/mptcp/pmkernel.c:1071 at marksubflowendpavailable net/mptcp/pmkernel.c:1071 [inline], CPU#1: syz.2.17/961 WARNING: net/mptcp/pmkernel.c:1071 at mptcpnlremovesubflowandsignaladdr net/mptcp/pmkernel.c:1103 [inline], CPU#1: syz.2.17/961 WARNING: net/mptcp/pmkernel.c:1071 at mptcppmnldeladdrdoit+0x81d/0x8f0 net/mptcp/pmkernel.c:1210, CPU#1: syz.2.17/961 Modules linked in: CPU: 1 UID: 0 PID: 961 Comm: syz.2.17 Not tainted 6.19.0-08368-gfafda3b4b06b #22 PREEMPT(full) Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.17.0-debian-1.17.0-1build1 04/01/2014 RIP: 0010:marksubflowendpavailable net/mptcp/pmkernel.c:1071 [inline] RIP: 0010:mptcpnlremovesubflowandsignaladdr net/mptcp/pmkernel.c:1103 [inline] RIP: 0010:mptcppmnldeladdrdoit+0x81d/0x8f0 net/mptcp/pmkernel.c:1210 Code: 89 c5 e8 46 30 6f fe e9 21 fd ff ff 49 83 ed 80 e8 38 30 6f fe 4c 89 ef be 03 00 00 00 e8 db 49 df fe eb ac e8 24 30 6f fe 90 <0f> 0b 90 e9 1d ff ff ff e8 16 30 6f fe eb 05 e8 0f 30 6f fe e8 9a RSP: 0018:ffffc90001663880 EFLAGS: 00010293 RAX: ffffffff82de1a6c RBX: 0000000000000000 RCX: ffff88800722b500 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff8880158b22d0 R08: 0000000000010425 R09: ffffffffffffffff R10: ffffffff82de18ba R11: 0000000000000000 R12: ffff88800641a640 R13: ffff8880158b1880 R14: ffff88801ec3c900 R15: ffff88800641a650 FS: 00005555722c3500(0000) GS:ffff8880f909d000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f66346e0f60 CR3: 000000001607c000 CR4: 0000000000350ef0 Call Trace: <TASK> genlfamilyrcvmsgdoit+0x117/0x180 net/netlink/genetlink.c:1115 genlfamilyrcvmsg net/netlink/genetlink.c:1195 [inline] genlrcvmsg+0x3a8/0x3f0 net/netlink/genetlink.c:1210 netlinkrcvskb+0x16d/0x240 net/netlink/afnetlink.c:2550 genlrcv+0x28/0x40 net/netlink/genetlink.c:1219 netlinkunicastkernel net/netlink/afnetlink.c:1318 [inline] netlinkunicast+0x3e9/0x4c0 net/netlink/afnetlink.c:1344 netlinksendmsg+0x4aa/0x5b0 net/netlink/afnetlink.c:1894 socksendmsgnosec net/socket.c:727 [inline] socksendmsg+0xc9/0xf0 net/socket.c:742 syssendmsg+0x272/0x3b0 net/socket.c:2592 syssendmsg+0x2de/0x320 net/socket.c:2646 syssendmsg net/socket.c:2678 [inline] dosyssendmsg net/socket.c:2683 [inline] sesyssendmsg net/socket.c:2681 [inline] x64syssendmsg+0x110/0x1a0 net/socket.c:2681 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0x143/0x440 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7f66346f826d Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffc83d8bdc8 EFLAGS: 00000246 ORIGRAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f6634985fa0 RCX: 00007f66346f826d RDX: 00000000040000b0 RSI: 0000200000000740 RDI: 0000000000000007 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6634985fa8 R13: 00007f6634985fac R14: 0000000000000000 R15: 0000000000001770 </TASK>
The actions that caused that seem to be:
- Set the MPTCP subflows limit to 0 - Create an MPTCP endpoint with both the 'signal' and 'subflow' flags - Create a new MPTCP connection from a different address: an ADDADDR linked to the MPTCP endpoint will be sent ('signal' flag), but no subflows is initiated ('subflow' flag) - Remove the MPTCP endpoint
---truncated---