Re: [syzbot] [lsm?] WARNING in put_cred_rcu

[syzbot <syzbot+553c4078ab14e3cf3358@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in destroy_super_work

------------[ cut here ]------------
WARNING: CPU: 0 PID: 22406 at ./include/linux/ns_common.h:261 __ns_ref_put include/linux/ns_common.h:261 [inline]
WARNING: CPU: 0 PID: 22406 at ./include/linux/ns_common.h:261 put_user_ns include/linux/user_namespace.h:189 [inline]
WARNING: CPU: 0 PID: 22406 at ./include/linux/ns_common.h:261 destroy_super_work+0x15c/0x1a0 fs/super.c:280
Modules linked in:
CPU: 0 UID: 0 PID: 22406 Comm: kworker/0:5 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events destroy_super_work
RIP: 0010:__ns_ref_put include/linux/ns_common.h:261 [inline]
RIP: 0010:put_user_ns include/linux/user_namespace.h:189 [inline]
RIP: 0010:destroy_super_work+0x15c/0x1a0 fs/super.c:280
Code: 4a 65 ff 48 81 c3 a8 fc ff ff 48 89 df e8 8c 4a 65 ff 4c 89 f7 5b 41 5c 41 5d 41 5e 41 5f 5d e9 6a 66 e2 ff e8 c5 48 88 ff 90 <0f> 0b 90 e9 6d ff ff ff e8 b7 48 88 ff 4c 89 e7 be 03 00 00 00 e8
RSP: 0018:ffffc90003b7fa28 EFLAGS: 00010293
RAX: ffffffff823893cb RBX: ffff88805ca22898 RCX: ffff88807b670000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000000
RBP: 0000000000000004 R08: ffff8880277fc9e3 R09: 1ffff11004eff93c
R10: dffffc0000000000 R11: ffffed1004eff93d R12: ffff8880277fc9e0
R13: dffffc0000000000 R14: ffff88805ca22000 R15: ffff8880277fc850
FS:  0000000000000000(0000) GS:ffff888125cf2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4d20c10286 CR3: 000000000df38000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         00f5a3b5 DO NOT MERGE - This is purely for testing a b..
git tree:       https://github.com/brauner/linux.git namespace-6.19.fixes
console output: https://syzkaller.appspot.com/x/log.txt?x=17a46a58580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e31f5f45f87b6763
dashboard link: https://syzkaller.appspot.com/bug?extid=553c4078ab14e3cf3358
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.