[moderation] [fs?] general protection fault in put_mnt_ns

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6d7e7251d03f Add linux-next specific files for 20251113
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11896d32580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d5f85f74e3fd5fa
dashboard link: https://syzkaller.appspot.com/bug?extid=a4aa2dfebffeae88ffa2
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a02c23eee588/disk-6d7e7251.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/908a9ce52ce3/vmlinux-6d7e7251.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5dbce2dc2d84/bzImage-6d7e7251.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a4aa2d...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 0 UID: 0 PID: 6270 Comm: syz.4.120 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:is_ns_init_id include/linux/ns_common.h:25 [inline]
RIP: 0010:__ns_ref_put include/linux/ns_common.h:70 [inline]
RIP: 0010:put_mnt_ns+0x34/0x2f0 fs/namespace.c:6062
Code: 55 41 54 53 48 89 fb e8 ca e7 7d ff 48 85 db 0f 84 df 00 00 00 49 bc 00 00 00 00 00 fc ff df 4c 8d 73 20 4d 89 f5 49 c1 ed 03 <43> 80 7c 25 00 00 74 08 4c 89 f7 e8 8c 95 e4 ff 4d 8b 3e 31 ff 4c
RSP: 0018:ffffc900052b7960 EFLAGS: 00010203
RAX: ffffffff8243b886 RBX: fffffffffffffff4 RCX: 0000000000080000
RDX: ffffc9000cc0b000 RSI: 000000000004128d RDI: 000000000004128e
RBP: fffffffffffffff4 R08: ffffffff8f7dd077 R09: 1ffffffff1efba0e
R10: dffffc0000000000 R11: fffffbfff1efba0f R12: dffffc0000000000
R13: 0000000000000002 R14: 0000000000000014 R15: ffff88802ad90958
FS: 00007f69aaa526c0(0000) GS:ffff888125ec1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000380 CR3: 0000000035054000 CR4: 00000000003526f0
Call Trace:
<TASK>
nsproxy_free+0x3c/0x7c0 kernel/nsproxy.c:65
__free_nsproxy_free kernel/nsproxy.c:76 [inline]
create_new_namespaces+0x47a/0x540 kernel/nsproxy.c:132
copy_namespaces+0x438/0x4b0 kernel/nsproxy.c:166
copy_process+0x168f/0x3930 kernel/fork.c:2183
kernel_clone+0x21e/0x850 kernel/fork.c:2609
__do_sys_clone kernel/fork.c:2750 [inline]
__se_sys_clone kernel/fork.c:2734 [inline]
__x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2734
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: 0033:0x7f69a9b8f6c9
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:00007f69aaa51fe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f69a9de5fa0 RCX: 00007f69a9b8f6c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000b21e0000
RBP: 00007f69a9c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f69a9de6038 R14: 00007f69a9de5fa0 R15: 00007ffee58cd938
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:is_ns_init_id include/linux/ns_common.h:25 [inline]
RIP: 0010:__ns_ref_put include/linux/ns_common.h:70 [inline]
RIP: 0010:put_mnt_ns+0x34/0x2f0 fs/namespace.c:6062
Code: 55 41 54 53 48 89 fb e8 ca e7 7d ff 48 85 db 0f 84 df 00 00 00 49 bc 00 00 00 00 00 fc ff df 4c 8d 73 20 4d 89 f5 49 c1 ed 03 <43> 80 7c 25 00 00 74 08 4c 89 f7 e8 8c 95 e4 ff 4d 8b 3e 31 ff 4c
RSP: 0018:ffffc900052b7960 EFLAGS: 00010203
RAX: ffffffff8243b886 RBX: fffffffffffffff4 RCX: 0000000000080000
RDX: ffffc9000cc0b000 RSI: 000000000004128d RDI: 000000000004128e
RBP: fffffffffffffff4 R08: ffffffff8f7dd077 R09: 1ffffffff1efba0e
R10: dffffc0000000000 R11: fffffbfff1efba0f R12: dffffc0000000000
R13: 0000000000000002 R14: 0000000000000014 R15: ffff88802ad90958
FS: 00007f69aaa526c0(0000) GS:ffff888125ec1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30721ff8 CR3: 0000000035054000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 55 push %rbp
1: 41 54 push %r12
3: 53 push %rbx
4: 48 89 fb mov %rdi,%rbx
7: e8 ca e7 7d ff call 0xff7de7d6
c: 48 85 db test %rbx,%rbx
f: 0f 84 df 00 00 00 je 0xf4
15: 49 bc 00 00 00 00 00 movabs $0xdffffc0000000000,%r12
1c: fc ff df
1f: 4c 8d 73 20 lea 0x20(%rbx),%r14
23: 4d 89 f5 mov %r14,%r13
26: 49 c1 ed 03 shr $0x3,%r13
* 2a: 43 80 7c 25 00 00 cmpb $0x0,0x0(%r13,%r12,1) <-- trapping instruction
30: 74 08 je 0x3a
32: 4c 89 f7 mov %r14,%rdi
35: e8 8c 95 e4 ff call 0xffe495c6
3a: 4d 8b 3e mov (%r14),%r15
3d: 31 ff xor %edi,%edi
3f: 4c rex.WR


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