general protection fault in __is_local_mountpoint

Status: upstream: reported C repro on 2026/07/20 20:39
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+8fc31d8f0ff9600238a1@syzkaller.appspotmail.com
First crash: 4d00h, last: 3d21h
Bug presence (2)
Date Name Commit Repro Result
2026/07/21 lts (merge base) c86c4726e7f0 C [report] lost connection to test machine
2026/07/21 upstream (ToT) b95f03f04d47 C [report] lost connection to test machine

Sample crash report:
general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 1 PID: 795 Comm: syz.6.119 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
RIP: 0010:__is_local_mountpoint+0x56/0x1a0 fs/namespace.c:706
Code: 49 81 c6 30 08 00 00 4c 89 f0 48 c1 e8 03 80 3c 18 00 74 08 4c 89 f7 e8 b8 aa f0 ff 4d 8b 36 49 83 c6 18 4c 89 f0 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 f7 e8 9c aa f0 ff 4d 8b 3e 48 c7 c7 20 80
RSP: 0018:ffffc9000236f868 EFLAGS: 00010206
RAX: 0000000000000003 RBX: dffffc0000000000 RCX: ffff88811d4ca780
RDX: 0000000000000000 RSI: 0000000000010000 RDI: ffff888113557770
RBP: ffffc9000236f8a0 R08: ffff8881326cc827 R09: 1ffff110264d9904
R10: dffffc0000000000 R11: ffffed10264d9905 R12: 1ffff110264d931b
R13: 0000000000010000 R14: 0000000000000018 R15: 1ffff110226aaeee
FS:  0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f37a452ec6b CR3: 000000010de56000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 is_local_mountpoint fs/mount.h:142 [inline]
 vfs_rmdir+0x12d/0x450 fs/namei.c:4150
 incfs_kill_sb+0xfe/0x210 fs/incfs/vfs.c:1989
 deactivate_locked_super+0xa0/0x100 fs/super.c:335
 deactivate_super+0xaf/0xe0 fs/super.c:366
 cleanup_mnt+0x44f/0x500 fs/namespace.c:1149
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1156
 task_work_run+0x127/0x190 kernel/task_work.c:188
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xb70/0x29a0 kernel/exit.c:890
 do_group_exit+0x149/0x310 kernel/exit.c:1004
 get_signal+0x64f/0x1430 kernel/signal.c:2908
 arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fefa8517e99
Code: Unable to access opcode bytes at RIP 0x7fefa8517e6f.
RSP: 002b:00007fefa83790e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fefa879ffa8 RCX: 00007fefa8517e99
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fefa879ffa8
RBP: 00007fefa879ffa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fefa87a0038 R14: 00007ffcb22e01d0 R15: 00007ffcb22e02b8
 </TASK>
Modules linked in:
---[ end trace 59eef9fbe586ed56 ]---
RIP: 0010:__is_local_mountpoint+0x56/0x1a0 fs/namespace.c:706
Code: 49 81 c6 30 08 00 00 4c 89 f0 48 c1 e8 03 80 3c 18 00 74 08 4c 89 f7 e8 b8 aa f0 ff 4d 8b 36 49 83 c6 18 4c 89 f0 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 f7 e8 9c aa f0 ff 4d 8b 3e 48 c7 c7 20 80
RSP: 0018:ffffc9000236f868 EFLAGS: 00010206
RAX: 0000000000000003 RBX: dffffc0000000000 RCX: ffff88811d4ca780
RDX: 0000000000000000 RSI: 0000000000010000 RDI: ffff888113557770
RBP: ffffc9000236f8a0 R08: ffff8881326cc827 R09: 1ffff110264d9904
R10: dffffc0000000000 R11: ffffed10264d9905 R12: 1ffff110264d931b
R13: 0000000000010000 R14: 0000000000000018 R15: 1ffff110226aaeee
FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 000000010de56000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	49 81 c6 30 08 00 00 	add    $0x830,%r14
   7:	4c 89 f0             	mov    %r14,%rax
   a:	48 c1 e8 03          	shr    $0x3,%rax
   e:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
  12:	74 08                	je     0x1c
  14:	4c 89 f7             	mov    %r14,%rdi
  17:	e8 b8 aa f0 ff       	call   0xfff0aad4
  1c:	4d 8b 36             	mov    (%r14),%r14
  1f:	49 83 c6 18          	add    $0x18,%r14
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1) <-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 f7             	mov    %r14,%rdi
  33:	e8 9c aa f0 ff       	call   0xfff0aad4
  38:	4d 8b 3e             	mov    (%r14),%r15
  3b:	48                   	rex.W
  3c:	c7                   	.byte 0xc7
  3d:	c7                   	(bad)
  3e:	20                   	.byte 0x20
  3f:	80                   	.byte 0x80

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/20 22:02 android13-5.15-lts dc151d2e3144 de6a700d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro #1 (corrupt fs)] [mounted in repro #2 (corrupt fs)] ci2-android-5-15 general protection fault in __is_local_mountpoint
2026/07/20 21:14 android13-5.15-lts dc151d2e3144 de6a700d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 general protection fault in __is_local_mountpoint
2026/07/20 20:29 android13-5.15-lts dc151d2e3144 de6a700d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 general protection fault in __is_local_mountpoint
2026/07/20 22:47 android13-5.15-lts dc151d2e3144 de6a700d .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro #1 (corrupt fs)] [mounted in repro #2 (corrupt fs)] ci2-android-5-15 general protection fault in __is_local_mountpoint
2026/07/20 19:42 android13-5.15-lts dc151d2e3144 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 general protection fault in __is_local_mountpoint
* Struck through repros no longer work on HEAD.