[syzbot] [nbd?] WARNING in nbd_add_socket

[syzbot] [nbd?] WARNING in nbd_add_socket

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b85966adbf5d Merge tag 'net-next-7.2' of git://git.kernel...
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=101f6d56580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a9f723a32776544
dashboard link: https://syzkaller.appspot.com/bug?extid=6b85d1e39a5b8ed9a954
compiler:       Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13584aae580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11fd7b7a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/780edcc3cc37/disk-b85966ad.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/967dd18c7ecd/vmlinux-b85966ad.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cf9fa92c90ff/bzImage-b85966ad.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6b85d1e39a5b8ed9a954@syzkaller.appspotmail.com

netlink: 3936 bytes leftover after parsing attributes in process `syz.0.25'.
------------[ cut here ]------------
!sock_allow_reclassification(sk)
WARNING: drivers/block/nbd.c:1249 at nbd_reclassify_socket drivers/block/nbd.c:1249 [inline], CPU#0: syz.0.25/5992
WARNING: drivers/block/nbd.c:1249 at nbd_add_socket+0xf35/0x12c0 drivers/block/nbd.c:1293, CPU#0: syz.0.25/5992
Modules linked in:

CPU: 0 UID: 0 PID: 5992 Comm: syz.0.25 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:nbd_reclassify_socket drivers/block/nbd.c:1249 [inline]
RIP: 0010:nbd_add_socket+0xf35/0x12c0 drivers/block/nbd.c:1293
Code: f7 e8 6f b5 20 fc bf e0 01 00 00 49 03 3e 48 c7 c6 40 02 55 8c e8 2b a8 1b fb b8 f0 ff ff ff e9 b2 fd ff ff e8 ac 60 b5 fb 90 <0f> 0b 90 e9 16 f8 ff ff e8 5e 2e 97 05 44 89 e9 80 e1 07 fe c1 38
RSP: 0018:ffffc90002ef7160 EFLAGS: 00010293

RAX: ffffffff86109574 RBX: 1ffff1100651ddb9 RCX: ffff888020b68000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90002ef7250 R08: ffff888035af2bdf R09: 1ffff11006b5e57b
R10: dffffc0000000000 R11: ffffed1006b5e57c R12: ffff8880328eec00
R13: 1ffff920005dee38 R14: dffffc0000000000 R15: 0000000000000001
FS:  00007fcc9d5dd6c0(0000) GS:ffff88812527c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f81a8ab50f0 CR3: 0000000078780000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nbd_genl_connect+0x133d/0x1c10 drivers/block/nbd.c:2254
 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x9b9/0xa20 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmsg net/socket.c:2770 [inline]
 __do_sys_sendmsg net/socket.c:2775 [inline]
 __se_sys_sendmsg net/socket.c:2773 [inline]
 __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcc9df9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fcc9d5dd028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fcc9e216090 RCX: 00007fcc9df9ce59
RDX: 0000000000004040 RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007fcc9e032d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fcc9e216128 R14: 00007fcc9e216090 R15: 00007ffc8f827678
 </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 syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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