[syzbot] [kernel?] general protection fault in put_ipc_ns

[syzbot <syzbot+b4c65e7d749285a82467@syzkaller.appspotmail.com>]

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=15e4c914580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8a6b17620801a7cb
dashboard link: https://syzkaller.appspot.com/bug?extid=b4c65e7d749285a82467
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=154ec658580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162aeb42580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ab5308631192/disk-6d7e7251.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/53e266b1dfe2/vmlinux-6d7e7251.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a24e6bca1ac0/bzImage-6d7e7251.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b4c65e7d749285a82467@syzkaller.appspotmail.com

RSP: 002b:00007fff968e5608 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007fe58a3e5fa0 RCX: 00007fe58a18f6c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000006a040000
RBP: 00007fff968e5660 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fe58a3e5fa0 R14: 00007fe58a3e5fa0 R15: 0000000000000001
 </TASK>
Oops: general protection fault, probably for non-canonical address 0xdffffc000000012f: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000978-0x000000000000097f]
CPU: 1 UID: 0 PID: 6021 Comm: syz.0.17 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_dec_and_lock include/linux/ns_common.h:108 [inline]
RIP: 0010:put_ipc_ns+0x7f/0x3d0 ipc/namespace.c:204
Code: b8 f1 f1 f1 f1 00 f3 f3 f3 4b 89 44 3d 00 e8 08 6b 85 fd 48 85 db 0f 84 ea 00 00 00 4c 8d a3 88 09 00 00 4d 89 e6 49 c1 ee 03 <43> 80 3c 3e 00 74 08 4c 89 e7 e8 02 c4 eb fd 4d 8b 3c 24 31 ff 4c
RSP: 0018:ffffc900034a7c60 EFLAGS: 00010203
RAX: ffffffff843c7548 RBX: fffffffffffffff4 RCX: ffff88805c080000
RDX: 0000000000000000 RSI: 0000000000000002 RDI: fffffffffffffff4
RBP: ffffc900034a7cf8 R08: ffff8880325cd59f R09: 1ffff110064b9ab3
R10: dffffc0000000000 R11: ffffed10064b9ab4 R12: 000000000000097c
R13: 1ffff92000694f8c R14: 000000000000012f R15: dffffc0000000000
FS:  0000555582176500(0000) GS:ffff888125b78000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555582176808 CR3: 00000000751d2000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nsproxy_free+0x1ef/0x7c0 kernel/nsproxy.c:67
 __free_nsproxy_free kernel/nsproxy.c:76 [inline]
 create_new_namespaces+0x47a/0x540 kernel/nsproxy.c:132
 unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:197
 ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3129
 __do_sys_unshare kernel/fork.c:3200 [inline]
 __se_sys_unshare kernel/fork.c:3198 [inline]
 __x64_sys_unshare+0x38/0x50 kernel/fork.c:3198
 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: 0033:0x7fe58a18f6c9
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:00007fff968e5608 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007fe58a3e5fa0 RCX: 00007fe58a18f6c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000006a040000
RBP: 00007fff968e5660 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fe58a3e5fa0 R14: 00007fe58a3e5fa0 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:is_ns_init_id include/linux/ns_common.h:25 [inline]
RIP: 0010:__ns_ref_dec_and_lock include/linux/ns_common.h:108 [inline]
RIP: 0010:put_ipc_ns+0x7f/0x3d0 ipc/namespace.c:204
Code: b8 f1 f1 f1 f1 00 f3 f3 f3 4b 89 44 3d 00 e8 08 6b 85 fd 48 85 db 0f 84 ea 00 00 00 4c 8d a3 88 09 00 00 4d 89 e6 49 c1 ee 03 <43> 80 3c 3e 00 74 08 4c 89 e7 e8 02 c4 eb fd 4d 8b 3c 24 31 ff 4c
RSP: 0018:ffffc900034a7c60 EFLAGS: 00010203
RAX: ffffffff843c7548 RBX: fffffffffffffff4 RCX: ffff88805c080000
RDX: 0000000000000000 RSI: 0000000000000002 RDI: fffffffffffffff4
RBP: ffffc900034a7cf8 R08: ffff8880325cd59f R09: 1ffff110064b9ab3
R10: dffffc0000000000 R11: ffffed10064b9ab4 R12: 000000000000097c
R13: 1ffff92000694f8c R14: 000000000000012f R15: dffffc0000000000
FS:  0000555582176500(0000) GS:ffff888125b78000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555582176808 CR3: 00000000751d2000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	b8 f1 f1 f1 f1       	mov    $0xf1f1f1f1,%eax
   5:	00 f3                	add    %dh,%bl
   7:	f3 f3 4b 89 44 3d 00 	repz xrelease mov %rax,0x0(%r13,%r15,1)
   e:	e8 08 6b 85 fd       	call   0xfd856b1b
  13:	48 85 db             	test   %rbx,%rbx
  16:	0f 84 ea 00 00 00    	je     0x106
  1c:	4c 8d a3 88 09 00 00 	lea    0x988(%rbx),%r12
  23:	4d 89 e6             	mov    %r12,%r14
  26:	49 c1 ee 03          	shr    $0x3,%r14
* 2a:	43 80 3c 3e 00       	cmpb   $0x0,(%r14,%r15,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 e7             	mov    %r12,%rdi
  34:	e8 02 c4 eb fd       	call   0xfdebc43b
  39:	4d 8b 3c 24          	mov    (%r12),%r15
  3d:	31 ff                	xor    %edi,%edi
  3f:	4c                   	rex.WR


---
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