[syzbot] [mptcp?] WARNING in mptcp_pm_nl_del_addr_doit

Hello,

syzbot found the following issue on:

HEAD commit:    6548d364a3e8 Merge tag 'cgroup-for-6.18-rc2-fixes' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11da4e7c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f953a3e1b3e60637
dashboard link: https://syzkaller.appspot.com/bug?extid=f56f7d56e2c6e11a01b6
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a6472a8e035a/disk-6548d364.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1547185ddf28/vmlinux-6548d364.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d4610741deb8/bzImage-6548d364.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f56f7d56e2c6e11a01b6@syzkaller.appspotmail.com

netlink: 8 bytes leftover after parsing attributes in process `syz.7.6472'.
netlink: 8 bytes leftover after parsing attributes in process `syz.7.6472'.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 27976 at net/mptcp/pm_kernel.c:1053 __mark_subflow_endp_available net/mptcp/pm_kernel.c:1053 [inline]
WARNING: CPU: 0 PID: 27976 at net/mptcp/pm_kernel.c:1053 mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1088 [inline]
WARNING: CPU: 0 PID: 27976 at net/mptcp/pm_kernel.c:1053 mptcp_pm_nl_del_addr_doit+0xe2c/0x11d0 net/mptcp/pm_kernel.c:1190
Modules linked in:
CPU: 0 UID: 0 PID: 27976 Comm: syz.7.6472 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1053 [inline]
RIP: 0010:mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1088 [inline]
RIP: 0010:mptcp_pm_nl_del_addr_doit+0xe2c/0x11d0 net/mptcp/pm_kernel.c:1190
Code: 01 00 00 49 89 c6 e8 93 b2 82 f6 e9 ed fb ff ff e8 89 b2 82 f6 48 89 df be 03 00 00 00 e8 ac 8d 53 f9 eb 9c e8 75 b2 82 f6 90 <0f> 0b 90 e9 90 fe ff ff 89 d9 80 e1 07 38 c1 0f 8c d9 fb ff ff 48
RSP: 0018:ffffc9000c3e71a0 EFLAGS: 00010283
RAX: ffffffff8b3d917b RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc90019844000 RSI: 0000000000009d14 RDI: 0000000000009d15
RBP: ffffc9000c3e73b0 R08: ffff88802f74eea7 R09: 1ffff11005ee9dd4
R10: dffffc0000000000 R11: ffffed1005ee9dd5 R12: ffff888068e67080
R13: ffff88802f74ee98 R14: ffff88802f74e400 R15: 1ffff11005ee9dd3
FS:  00007f57ed7746c0(0000) GS:ffff888125d06000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000020000000c038 CR3: 000000004ebf8000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x505/0x830 net/socket.c:2630
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
 __sys_sendmsg net/socket.c:2716 [inline]
 __do_sys_sendmsg net/socket.c:2721 [inline]
 __se_sys_sendmsg net/socket.c:2719 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f57ec98efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f57ed774038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f57ecbe6090 RCX: 00007f57ec98efc9
RDX: 000000002000c094 RSI: 0000200000000000 RDI: 0000000000000009
RBP: 00007f57eca11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f57ecbe6128 R14: 00007f57ecbe6090 R15: 00007ffeff6c13c8
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup