Re: [syzbot] [fuse?] general protection fault in task_work_cancel

["Günther Noack" <gnoack@google.com>]

On Sat, Mar 07, 2026 at 07:46:25PM -0800, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    4ae12d8bd9a8 Merge tag 'kbuild-fixes-7.0-2' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17dc475a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=779072223d02a312
> dashboard link: https://syzkaller.appspot.com/bug?extid=741e2278ef71fef03a10
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=130b075a580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/010ac4052aed/disk-4ae12d8b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/2aad8bef9031/vmlinux-4ae12d8b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fd350ec4896a/bzImage-4ae12d8b.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+741e2278ef71fef03a10@syzkaller.appspotmail.com
> 
> Oops: general protection fault, probably for non-canonical address 0xdffffc000000013c: 0000 [#1] SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x00000000000009e0-0x00000000000009e7]
> CPU: 1 UID: 0 PID: 13249 Comm: syz.1.1775 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
> RIP: 0010:task_work_pending include/linux/task_work.h:26 [inline]
> RIP: 0010:task_work_cancel_match kernel/task_work.c:124 [inline]
> RIP: 0010:task_work_cancel+0x8a/0x220 kernel/task_work.c:187
> Code: b8 f1 f1 f1 f1 f8 f3 f3 f3 4b 89 44 25 00 e8 ad b9 35 00 43 c6 44 25 04 00 49 89 de 48 81 c3 e0 09 00 00 49 89 df 49 c1 ef 03 <43> 80 3c 27 00 74 08 48 89 df e8 17 fe 9f 00 48 83 3b 00 75 51 e8
> RSP: 0018:ffffc9000ddffb20 EFLAGS: 00010216
> RAX: ffffffff818fdfc3 RBX: 00000000000009e0 RCX: ffff88805d5c3d00
> RDX: 0000000000000000 RSI: ffff888032f5c540 RDI: 0000000000000000
> RBP: ffffc9000ddffbd0 R08: ffffc9000ddffc97 R09: 1ffff92001bbff92
> R10: dffffc0000000000 R11: fffff52001bbff93 R12: dffffc0000000000
> R13: 1ffff92001bbff68 R14: 0000000000000000 R15: 000000000000013c
> FS:  00007f9c8a1cb6c0(0000) GS:ffff888125561000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000200000010000 CR3: 0000000059bf0000 CR4: 0000000000350ef0
> Call Trace:
>  <TASK>
>  cancel_tsync_works security/landlock/tsync.c:415 [inline]
>  landlock_restrict_sibling_threads+0xdc4/0x11f0 security/landlock/tsync.c:533
>  __do_sys_landlock_restrict_self security/landlock/syscalls.c:574 [inline]
>  __se_sys_landlock_restrict_self+0x540/0x810 security/landlock/syscalls.c:482
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f9c8939c799
> 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:00007f9c8a1cb028 EFLAGS: 00000246 ORIG_RAX: 00000000000001be
> RAX: ffffffffffffffda RBX: 00007f9c89616180 RCX: 00007f9c8939c799
> RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000003
> RBP: 00007f9c89432bd9 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f9c89616218 R14: 00007f9c89616180 R15: 00007ffee5d65d48
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:task_work_pending include/linux/task_work.h:26 [inline]
> RIP: 0010:task_work_cancel_match kernel/task_work.c:124 [inline]
> RIP: 0010:task_work_cancel+0x8a/0x220 kernel/task_work.c:187
> Code: b8 f1 f1 f1 f1 f8 f3 f3 f3 4b 89 44 25 00 e8 ad b9 35 00 43 c6 44 25 04 00 49 89 de 48 81 c3 e0 09 00 00 49 89 df 49 c1 ef 03 <43> 80 3c 27 00 74 08 48 89 df e8 17 fe 9f 00 48 83 3b 00 75 51 e8
> RSP: 0018:ffffc9000ddffb20 EFLAGS: 00010216
> RAX: ffffffff818fdfc3 RBX: 00000000000009e0 RCX: ffff88805d5c3d00
> RDX: 0000000000000000 RSI: ffff888032f5c540 RDI: 0000000000000000
> RBP: ffffc9000ddffbd0 R08: ffffc9000ddffc97 R09: 1ffff92001bbff92
> R10: dffffc0000000000 R11: fffff52001bbff93 R12: dffffc0000000000
> R13: 1ffff92001bbff68 R14: 0000000000000000 R15: 000000000000013c
> FS:  00007f9c8a1cb6c0(0000) GS:ffff888125561000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f810d34da08 CR3: 0000000059bf0000 CR4: 0000000000350ef0
> ----------------
> Code disassembly (best guess):
>    0:	b8 f1 f1 f1 f1       	mov    $0xf1f1f1f1,%eax
>    5:	f8                   	clc
>    6:	f3 f3 f3 4b 89 44 25 	repz repz xrelease mov %rax,0x0(%r13,%r12,1)
>    d:	00
>    e:	e8 ad b9 35 00       	call   0x35b9c0
>   13:	43 c6 44 25 04 00    	movb   $0x0,0x4(%r13,%r12,1)
>   19:	49 89 de             	mov    %rbx,%r14
>   1c:	48 81 c3 e0 09 00 00 	add    $0x9e0,%rbx
>   23:	49 89 df             	mov    %rbx,%r15
>   26:	49 c1 ef 03          	shr    $0x3,%r15
> * 2a:	43 80 3c 27 00       	cmpb   $0x0,(%r15,%r12,1) <-- trapping instruction
>   2f:	74 08                	je     0x39
>   31:	48 89 df             	mov    %rbx,%rdi
>   34:	e8 17 fe 9f 00       	call   0x9ffe50
>   39:	48 83 3b 00          	cmpq   $0x0,(%rbx)
>   3d:	75 51                	jne    0x90
>   3f:	e8                   	.byte 0xe8
> 
> 
> ---
> 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.

#syz fix: landlock: Fully release unused TSYNC work entries

(See https://github.com/google/syzkaller/blob/master/docs/syzbot.md#communication-with-syzbot)