[syzbot] [block?] general protection fault in lo_rw_aio

[syzbot <syzbot+cd8a9a308e879a4e2c28@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    43cfbdda5af6 Merge tag 'for-linus-iommufd' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101e4702580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4660d1ff2985517b
dashboard link: https://syzkaller.appspot.com/bug?extid=cd8a9a308e879a4e2c28
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0867fa0b89e8/disk-43cfbdda.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/754859270006/vmlinux-43cfbdda.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cd6cca8d06c9/bzImage-43cfbdda.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cd8a9a308e879a4e2c28@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000014: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7]
CPU: 1 UID: 0 PID: 1174 Comm: kworker/u8:8 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Workqueue: loop2 loop_workfn
RIP: 0010:file_inode include/linux/fs.h:1353 [inline]
RIP: 0010:kiocb_start_write include/linux/fs.h:2763 [inline]
RIP: 0010:lo_rw_aio+0xaa9/0xf00 drivers/block/loop.c:401
Code: 89 33 31 ff 8b 5c 24 44 89 de e8 32 2b 3f fc 85 db 0f 84 ca 00 00 00 48 8b 44 24 58 48 8d 98 a0 00 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 e8 ae a5 fc 4c 89 7c 24 10 48 8b
RSP: 0018:ffffc9000655f620 EFLAGS: 00010206
RAX: 0000000000000014 RBX: 00000000000000a0 RCX: ffff888029649ec0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000655f790 R08: 0000000000000000 R09: 0000000000000000
R10: ffffc9000655f6e3 R11: fffff52000cabede R12: ffff888026c9b090
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888026c9b0b0
FS:  0000000000000000(0000) GS:ffff88812620f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555591947a68 CR3: 000000005515a000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 do_req_filebacked drivers/block/loop.c:433 [inline]
 loop_handle_cmd drivers/block/loop.c:1925 [inline]
 loop_process_work+0x637/0x11b0 drivers/block/loop.c:1960
 process_one_work kernel/workqueue.c:3302 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3385
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3466
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:file_inode include/linux/fs.h:1353 [inline]
RIP: 0010:kiocb_start_write include/linux/fs.h:2763 [inline]
RIP: 0010:lo_rw_aio+0xaa9/0xf00 drivers/block/loop.c:401
Code: 89 33 31 ff 8b 5c 24 44 89 de e8 32 2b 3f fc 85 db 0f 84 ca 00 00 00 48 8b 44 24 58 48 8d 98 a0 00 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 e8 ae a5 fc 4c 89 7c 24 10 48 8b
RSP: 0018:ffffc9000655f620 EFLAGS: 00010206
RAX: 0000000000000014 RBX: 00000000000000a0 RCX: ffff888029649ec0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000655f790 R08: 0000000000000000 R09: 0000000000000000
R10: ffffc9000655f6e3 R11: fffff52000cabede R12: ffff888026c9b090
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888026c9b0b0
FS:  0000000000000000(0000) GS:ffff88812620f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555591947a68 CR3: 000000005515a000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	89 33                	mov    %esi,(%rbx)
   2:	31 ff                	xor    %edi,%edi
   4:	8b 5c 24 44          	mov    0x44(%rsp),%ebx
   8:	89 de                	mov    %ebx,%esi
   a:	e8 32 2b 3f fc       	call   0xfc3f2b41
   f:	85 db                	test   %ebx,%ebx
  11:	0f 84 ca 00 00 00    	je     0xe1
  17:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  1c:	48 8d 98 a0 00 00 00 	lea    0xa0(%rax),%rbx
  23:	48 89 d8             	mov    %rbx,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 df             	mov    %rbx,%rdi
  34:	e8 e8 ae a5 fc       	call   0xfca5af21
  39:	4c 89 7c 24 10       	mov    %r15,0x10(%rsp)
  3e:	48                   	rex.W
  3f:	8b                   	.byte 0x8b


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