[syzbot] [fs?] general protection fault in grab_requested_root

[syzbot <syzbot+9e03a9535ea65f687a44@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    dc855b77719f Merge tag 'irq-drivers-2026-02-09' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13136ae6580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=86c6013ce1247095
dashboard link: https://syzkaller.appspot.com/bug?extid=9e03a9535ea65f687a44
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15da0b3a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14e28e5a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a31372ead89f/disk-dc855b77.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/657357081566/vmlinux-dc855b77.xz
kernel image: https://storage.googleapis.com/syzbot-assets/278d7f265ba3/bzImage-dc855b77.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e03a9535ea65f687a44@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc000000001e: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000000f0-0x00000000000000f7]
CPU: 0 UID: 0 PID: 5998 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:mnt_ns_empty fs/mount.h:197 [inline]
RIP: 0010:grab_requested_root+0xde/0x3c0 fs/namespace.c:5636
Code: 02 00 00 49 39 5d 18 0f 84 cd 01 00 00 e8 0a 10 78 ff 48 8d bb 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 82 02 00 00 48 8b 83 08 01 00 00 48 85 c0 0f 84
RSP: 0018:ffffc90003027d88 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffffffffffea RCX: ffffffff828e8167
RDX: 000000000000001e RSI: ffffffff828e7fb6 RDI: 00000000000000f2
RBP: ffffc90003027db0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802b220000
R13: ffff88803156d4e0 R14: ffff88807b4d7028 R15: ffff88807b4d7010
FS:  000055555e0dd500(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002c608000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 do_statmount fs/namespace.c:5699 [inline]
 __do_sys_statmount+0x359/0x2440 fs/namespace.c:5949
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f12d359bf79
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:00007ffd0e2fee68 EFLAGS: 00000246 ORIG_RAX: 00000000000001c9
RAX: ffffffffffffffda RBX: 00007f12d3815fa0 RCX: 00007f12d359bf79
RDX: 00000000000001fe RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f12d36327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f12d3815fac R14: 00007f12d3815fa0 R15: 00007f12d3815fa0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:mnt_ns_empty fs/mount.h:197 [inline]
RIP: 0010:grab_requested_root+0xde/0x3c0 fs/namespace.c:5636
Code: 02 00 00 49 39 5d 18 0f 84 cd 01 00 00 e8 0a 10 78 ff 48 8d bb 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 82 02 00 00 48 8b 83 08 01 00 00 48 85 c0 0f 84
RSP: 0018:ffffc90003027d88 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffffffffffea RCX: ffffffff828e8167
RDX: 000000000000001e RSI: ffffffff828e7fb6 RDI: 00000000000000f2
RBP: ffffc90003027db0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802b220000
R13: ffff88803156d4e0 R14: ffff88807b4d7028 R15: ffff88807b4d7010
FS:  000055555e0dd500(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002c608000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	02 00                	add    (%rax),%al
   2:	00 49 39             	add    %cl,0x39(%rcx)
   5:	5d                   	pop    %rbp
   6:	18 0f                	sbb    %cl,(%rdi)
   8:	84 cd                	test   %cl,%ch
   a:	01 00                	add    %eax,(%rax)
   c:	00 e8                	add    %ch,%al
   e:	0a 10                	or     (%rax),%dl
  10:	78 ff                	js     0x11
  12:	48 8d bb 08 01 00 00 	lea    0x108(%rbx),%rdi
  19:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  20:	fc ff df
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 82 02 00 00    	jne    0x2b6
  34:	48 8b 83 08 01 00 00 	mov    0x108(%rbx),%rax
  3b:	48 85 c0             	test   %rax,%rax
  3e:	0f                   	.byte 0xf
  3f:	84                   	.byte 0x84


---
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