CVE-2026-43252: mptcp: pm: in-kernel: always set ID as avail when rm endp

In the Linux kernel, the following vulnerability has been resolved:

mptcp: pm: in-kernel: always set ID as avail when rm endp

Syzkaller managed to find a combination of actions that was generating this warning:

WARNING: net/mptcp/pmkernel.c:1074 at marksubflowendpavailable net/mptcp/pmkernel.c:1074 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pmkernel.c:1074 at mptcppmnlfullmesh net/mptcp/pmkernel.c:1446 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pmkernel.c:1074 at mptcppmnlsetflagsall net/mptcp/pmkernel.c:1474 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pmkernel.c:1074 at mptcppmnlsetflags+0x5de/0x640 net/mptcp/pmkernel.c:1538, CPU#1: syz.7.48/2535 Modules linked in: CPU: 1 UID: 0 PID: 2535 Comm: syz.7.48 Not tainted 6.18.0-03987-gea5f5e676cf5 #17 PREEMPT(voluntary) Hardware name: QEMU Ubuntu 25.10 PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 RIP: 0010:marksubflowendpavailable net/mptcp/pmkernel.c:1074 [inline] RIP: 0010:mptcppmnlfullmesh net/mptcp/pmkernel.c:1446 [inline] RIP: 0010:mptcppmnlsetflagsall net/mptcp/pmkernel.c:1474 [inline] RIP: 0010:mptcppmnlsetflags+0x5de/0x640 net/mptcp/pmkernel.c:1538 Code: 89 c7 e8 c5 8c 73 fe e9 f7 fd ff ff 49 83 ef 80 e8 b7 8c 73 fe 4c 89 ff be 03 00 00 00 e8 4a 29 e3 fe eb ac e8 a3 8c 73 fe 90 <0f> 0b 90 e9 3d ff ff ff e8 95 8c 73 fe b8 a1 ff ff ff eb 1a e8 89 RSP: 0018:ffffc9001535b820 EFLAGS: 00010287 netdevsim0: tunchrioctl cmd 1074025677 RAX: ffffffff82da294d RBX: 0000000000000001 RCX: 0000000000080000 RDX: ffffc900096d0000 RSI: 00000000000006d6 RDI: 00000000000006d7 netdevsim0: linktype set to 823 RBP: ffff88802cdb2240 R08: 00000000000104ae R09: ffffffffffffffff R10: ffffffff82da27d4 R11: 0000000000000000 R12: 0000000000000000 R13: ffff88801246d8c0 R14: ffffc9001535b8b8 R15: ffff88802cdb1800 FS: 00007fc6ac5a76c0(0000) GS:ffff8880f90c8000(0000) knlGS:0000000000000000 netlink: 'syz.3.50': attribute type 5 has an invalid length. CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 netlink: 1232 bytes leftover after parsing attributes in process syz.3.50'. CR2: 0000200000010000 CR3: 0000000025b1a000 CR4: 0000000000350ef0 Call Trace: <TASK> mptcppmsetflags net/mptcp/pmnetlink.c:277 [inline] mptcppmnlsetflagsdoit+0x1d7/0x210 net/mptcp/pmnetlink.c:282 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+0x4ab/0x5b0 net/netlink/afnetlink.c:1894 socksendmsgnosec net/socket.c:718 [inline] socksendmsg+0xc9/0xf0 net/socket.c:733 syssendmsg+0x272/0x3b0 net/socket.c:2608 syssendmsg+0x2de/0x320 net/socket.c:2662 syssendmsg net/socket.c:2694 [inline] dosyssendmsg net/socket.c:2699 [inline] sesyssendmsg net/socket.c:2697 [inline] x64syssendmsg+0x110/0x1a0 net/socket.c:2697 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xed/0x360 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7fc6adb66f6d 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:00007fc6ac5a6ff8 EFLAGS: 00000246 ORIGRAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007fc6addf5fa0 RCX: 00007fc6adb66f6d RDX: 0000000000048084 RSI: 00002000000002c0 RDI: 000000000000000e RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000 ---truncated---