[syzbot] [lsm?] WARNING in put_cred_rcu

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 17490bd0527f Add linux-next specific files for 20251104
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16c09bcd980000
kernel config: https://syzkaller.appspot.com/x/.config?x=9995c0d2611ab121
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
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1500a532580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12e0a114580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a4d318147846/disk-17490bd0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/86641a470170/vmlinux-17490bd0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/35c008a540c8/bzImage-17490bd0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+553c40...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: ./include/linux/ns_common.h:255 at __ns_ref_put include/linux/ns_common.h:255 [inline], CPU#0: syz.1.27/6120
WARNING: ./include/linux/ns_common.h:255 at put_user_ns include/linux/user_namespace.h:189 [inline], CPU#0: syz.1.27/6120
WARNING: ./include/linux/ns_common.h:255 at put_cred_rcu+0x2c5/0x340 kernel/cred.c:61, CPU#0: syz.1.27/6120
Modules linked in:
CPU: 0 UID: 0 PID: 6120 Comm: syz.1.27 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:__ns_ref_put include/linux/ns_common.h:255 [inline]
RIP: 0010:put_user_ns include/linux/user_namespace.h:189 [inline]
RIP: 0010:put_cred_rcu+0x2c5/0x340 kernel/cred.c:61
Code: 5c 41 5d 41 5e 41 5f 5d e9 b8 41 8d 00 e8 03 77 32 00 4c 89 e7 be 03 00 00 00 e8 d6 19 07 03 e9 b8 fe ff ff e8 ec 76 32 00 90 <0f> 0b 90 eb 9f e8 e1 76 32 00 4c 89 ff be 03 00 00 00 e8 b4 19 07
RSP: 0018:ffffc90000007ba8 EFLAGS: 00010246
RAX: ffffffff818ee5a4 RBX: ffff88801c3762a0 RCX: ffff888027350000
RDX: 0000000000000100 RSI: 0000000000000004 RDI: 0000000000000000
RBP: 0000000000000004 R08: ffff888073d31eab R09: 1ffff1100e7a63d5
R10: dffffc0000000000 R11: ffffed100e7a63d6 R12: dffffc0000000000
R13: ffff88801c376200 R14: ffff888073d31d18 R15: ffff888073d31ea8
FS: 00007fcce9f9d6c0(0000) GS:ffff888125a92000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555684fe808 CR3: 000000007ee2c000 CR4: 00000000003526f0
Call Trace:
<IRQ>
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x286/0x870 kernel/softirq.c:626
__do_softirq kernel/softirq.c:660 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:727
irq_exit_rcu+0x9/0x30 kernel/softirq.c:743
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1052
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x175/0x360 kernel/locking/lockdep.c:5872
Code: 00 00 00 00 9c 8f 44 24 30 f7 44 24 30 00 02 00 00 0f 85 cd 00 00 00 f7 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 bb 94 1a 11 <48> 3b 44 24 58 0f 85 f2 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e
RSP: 0018:ffffc90002ec5f58 EFLAGS: 00000206
RAX: c3b7b02cbda44300 RBX: 0000000000000000 RCX: c3b7b02cbda44300
RDX: 0000000000000000 RSI: ffffffff8dc69c71 RDI: ffffffff8be0fc60
RBP: ffffffff817420d5 R08: 0000000000000000 R09: ffffffff817420d5
R10: ffffc90002ec6118 R11: ffffffff81ad6a10 R12: 0000000000000002
R13: ffffffff8e33b520 R14: 0000000000000000 R15: 0000000000000246
rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
rcu_read_lock include/linux/rcupdate.h:867 [inline]
class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
unwind_next_frame+0xc2/0x2390 arch/x86/kernel/unwind_orc.c:479
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
save_stack+0xf5/0x1f0 mm/page_owner.c:165
__set_page_owner+0x8d/0x4c0 mm/page_owner.c:341
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3920
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5214
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2479
folio_alloc_mpol_noprof+0x39/0x70 mm/mempolicy.c:2498
shmem_alloc_folio mm/shmem.c:1900 [inline]
shmem_alloc_and_add_folio+0x423/0xf40 mm/shmem.c:1942
shmem_get_folio_gfp+0x59d/0x1660 mm/shmem.c:2565
shmem_get_folio mm/shmem.c:2671 [inline]
shmem_write_begin+0xf7/0x2b0 mm/shmem.c:3320
generic_perform_write+0x2c5/0x900 mm/filemap.c:4313
shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3495
__kernel_write_iter+0x428/0x910 fs/read_write.c:619
dump_emit_page fs/coredump.c:1298 [inline]
dump_user_range+0x8a0/0xc90 fs/coredump.c:1372
elf_core_dump+0x3369/0x3960 fs/binfmt_elf.c:2111
coredump_write+0x116c/0x1900 fs/coredump.c:1049
vfs_coredump+0x1db5/0x2a60 fs/coredump.c:1170
get_signal+0x1108/0x1340 kernel/signal.c:3019
arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:40 [inline]
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
irqentry_exit_to_user_mode+0x7e/0x170 kernel/entry/common.c:73
exc_page_fault+0xab/0x100 arch/x86/mm/fault.c:1535
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7fcce918f6d1
Code: 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 83 c8 ff c3 66 2e 0f 1f
RSP: 002b:0000000000000010 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007fcce93e5fa0 RCX: 00007fcce918f6c9
RDX: 0000000000000000 RSI: 0000000000000010 RDI: 498144ee5f62e049
RBP: 00007fcce9211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007fcce93e6038 R14: 00007fcce93e5fa0 R15: 00007ffd4dc9bfc8
</TASK>
----------------
Code disassembly (best guess):
0: 00 00 add %al,(%rax)
2: 00 00 add %al,(%rax)
4: 9c pushf
5: 8f 44 24 30 pop 0x30(%rsp)
9: f7 44 24 30 00 02 00 testl $0x200,0x30(%rsp)
10: 00
11: 0f 85 cd 00 00 00 jne 0xe4
17: f7 44 24 08 00 02 00 testl $0x200,0x8(%rsp)
1e: 00
1f: 74 01 je 0x22
21: fb sti
22: 65 48 8b 05 bb 94 1a mov %gs:0x111a94bb(%rip),%rax # 0x111a94e5
29: 11
* 2a: 48 3b 44 24 58 cmp 0x58(%rsp),%rax <-- trapping instruction
2f: 0f 85 f2 00 00 00 jne 0x127
35: 48 83 c4 60 add $0x60,%rsp
39: 5b pop %rbx
3a: 41 5c pop %r12
3c: 41 5d pop %r13
3e: 41 5e pop %r14


---
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[Hillf Danton]

> Date: Fri, 07 Nov 2025 06:05:27 -0800

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 17490bd0527f Add linux-next specific files for 20251104
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16c09bcd980000
> kernel config: https://syzkaller.appspot.com/x/.config?x=9995c0d2611ab121
> 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
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1500a532580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12e0a114580000

#syz test https://github.com/brauner/linux.git namespace-6.19.fixes

[syzbot]

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.