CVE-2026-23321

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> mptcp: pm: in-kernel: always mark signal+subflow endp as used<br /> <br /> Syzkaller managed to find a combination of actions that was generating<br /> this warning:<br /> <br /> msk-&gt;pm.local_addr_used == 0<br /> WARNING: net/mptcp/pm_kernel.c:1071 at __mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline], CPU#1: syz.2.17/961<br /> WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1103 [inline], CPU#1: syz.2.17/961<br /> WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_pm_nl_del_addr_doit+0x81d/0x8f0 net/mptcp/pm_kernel.c:1210, CPU#1: syz.2.17/961<br /> Modules linked in:<br /> CPU: 1 UID: 0 PID: 961 Comm: syz.2.17 Not tainted 6.19.0-08368-gfafda3b4b06b #22 PREEMPT(full)<br /> 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<br /> RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline]<br /> RIP: 0010:mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1103 [inline]<br /> RIP: 0010:mptcp_pm_nl_del_addr_doit+0x81d/0x8f0 net/mptcp/pm_kernel.c:1210<br /> 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 0b 90 e9 1d ff ff ff e8 16 30 6f fe eb 05 e8 0f 30 6f fe e8 9a<br /> RSP: 0018:ffffc90001663880 EFLAGS: 00010293<br /> RAX: ffffffff82de1a6c RBX: 0000000000000000 RCX: ffff88800722b500<br /> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000<br /> RBP: ffff8880158b22d0 R08: 0000000000010425 R09: ffffffffffffffff<br /> R10: ffffffff82de18ba R11: 0000000000000000 R12: ffff88800641a640<br /> R13: ffff8880158b1880 R14: ffff88801ec3c900 R15: ffff88800641a650<br /> FS: 00005555722c3500(0000) GS:ffff8880f909d000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: 00007f66346e0f60 CR3: 000000001607c000 CR4: 0000000000350ef0<br /> Call Trace:<br /> <br /> genl_family_rcv_msg_doit+0x117/0x180 net/netlink/genetlink.c:1115<br /> genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]<br /> genl_rcv_msg+0x3a8/0x3f0 net/netlink/genetlink.c:1210<br /> netlink_rcv_skb+0x16d/0x240 net/netlink/af_netlink.c:2550<br /> genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219<br /> netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]<br /> netlink_unicast+0x3e9/0x4c0 net/netlink/af_netlink.c:1344<br /> netlink_sendmsg+0x4aa/0x5b0 net/netlink/af_netlink.c:1894<br /> sock_sendmsg_nosec net/socket.c:727 [inline]<br /> __sock_sendmsg+0xc9/0xf0 net/socket.c:742<br /> ____sys_sendmsg+0x272/0x3b0 net/socket.c:2592<br /> ___sys_sendmsg+0x2de/0x320 net/socket.c:2646<br /> __sys_sendmsg net/socket.c:2678 [inline]<br /> __do_sys_sendmsg net/socket.c:2683 [inline]<br /> __se_sys_sendmsg net/socket.c:2681 [inline]<br /> __x64_sys_sendmsg+0x110/0x1a0 net/socket.c:2681<br /> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]<br /> do_syscall_64+0x143/0x440 arch/x86/entry/syscall_64.c:94<br /> entry_SYSCALL_64_after_hwframe+0x77/0x7f<br /> RIP: 0033:0x7f66346f826d<br /> 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 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48<br /> RSP: 002b:00007ffc83d8bdc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e<br /> RAX: ffffffffffffffda RBX: 00007f6634985fa0 RCX: 00007f66346f826d<br /> RDX: 00000000040000b0 RSI: 0000200000000740 RDI: 0000000000000007<br /> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000<br /> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6634985fa8<br /> R13: 00007f6634985fac R14: 0000000000000000 R15: 0000000000001770<br /> <br /> <br /> The actions that caused that seem to be:<br /> <br /> - Set the MPTCP subflows limit to 0<br /> - Create an MPTCP endpoint with both the &amp;#39;signal&amp;#39; and &amp;#39;subflow&amp;#39; flags<br /> - Create a new MPTCP connection from a different address: an ADD_ADDR<br /> linked to the MPTCP endpoint will be sent (&amp;#39;signal&amp;#39; flag), but no<br /> subflows is initiated (&amp;#39;subflow&amp;#39; flag)<br /> - Remove the MPTCP endpoint<br /> <br /> ---truncated---