[v6.1] divide error in comedi_inc_scan_progress

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50cbba13faa2 Linux 6.1.159
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1285da1a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6a5cbd268406bf43
dashboard link: https://syzkaller.appspot.com/bug?extid=2bcaaae2c36c1b70a448
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/50ceb00b1b39/disk-50cbba13.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ebb8883b9a29/vmlinux-50cbba13.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7edc2a795f03/bzImage-50cbba13.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2bcaaa...@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5683 Comm: syz.2.251 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:comedi_inc_scan_progress+0x19e/0x430 drivers/comedi/drivers.c:562
Code: b6 0c 19 84 c9 0f 85 b8 01 00 00 03 45 34 4c 8d a5 88 00 00 00 4c 89 e1 48 c1 e9 03 0f b6 0c 19 84 c9 0f 85 c7 01 00 00 31 d2 <41> f7 34 24 41 89 17 45 89 ec eb 0f e8 c1 77 c7 f9 48 bb 00 00 00
RSP: 0018:ffffc90000007c80 EFLAGS: 00010046
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88807c318400 R08: ffff88807c318400 R09: fffff52001a53601
R10: fffff52001a53601 R11: 1ffff92001a53600 R12: ffff88807c318488
R13: 0000000000000002 R14: 0000000000000000 R15: ffff88807c318434
FS: 00007fc94c4466c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc94c425d58 CR3: 000000001b692000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
comedi_buf_write_samples+0x36e/0x5d0 drivers/comedi/comedi_buf.c:646
das16m1_handler+0x213/0x4b0 drivers/comedi/drivers/das16m1.c:413
das16m1_interrupt+0xa7/0x170 drivers/comedi/drivers/das16m1.c:470
__handle_irq_event_percpu+0x298/0xa30 kernel/irq/handle.c:158
handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
handle_irq_event+0x87/0x1e0 kernel/irq/handle.c:210
handle_edge_irq+0x243/0xb20 kernel/irq/chip.c:819
generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
handle_irq arch/x86/kernel/irq.c:233 [inline]
__common_interrupt+0xd7/0x1e0 arch/x86/kernel/irq.c:252
common_interrupt+0xb0/0xd0 arch/x86/kernel/irq.c:242
</IRQ>
<TASK>
asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:682
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
Code: 74 05 e8 6e be 6c f7 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 16 44 3d f7 65 8b 05 a7 f1 e7 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc9000cd375c0 EFLAGS: 00000206
RAX: ccc2f72316c8b500 RBX: 0000000000000a06 RCX: ccc2f72316c8b500
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: 0000000000000001
RBP: ffffc9000cd37658 R08: dffffc0000000000 R09: fffffbfff211905e
R10: fffffbfff211905e R11: 1ffffffff211905d R12: dffffc0000000000
R13: 1ffff1100a99f046 R14: ffff888054cf81d0 R15: 1ffff920019a6eb8
spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
__skb_try_recv_datagram+0x179/0x4d0 net/core/datagram.c:265
__unix_dgram_recvmsg+0x2d1/0xd70 net/unix/af_unix.c:2451
____sys_recvmsg+0x292/0x580 net/socket.c:-1
___sys_recvmsg+0x1b2/0x510 net/socket.c:2780
do_recvmmsg+0x359/0x7d0 net/socket.c:2874
__sys_recvmmsg net/socket.c:2953 [inline]
__do_sys_recvmmsg net/socket.c:2976 [inline]
__se_sys_recvmmsg net/socket.c:2969 [inline]
__x64_sys_recvmmsg+0x18d/0x240 net/socket.c:2969
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc94b58f749
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:00007fc94c446038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007fc94b7e6090 RCX: 00007fc94b58f749
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000005
RBP: 00007fc94b613f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc94b7e6128 R14: 00007fc94b7e6090 R15: 00007ffe8637c9b8
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:comedi_inc_scan_progress+0x19e/0x430 drivers/comedi/drivers.c:562
Code: b6 0c 19 84 c9 0f 85 b8 01 00 00 03 45 34 4c 8d a5 88 00 00 00 4c 89 e1 48 c1 e9 03 0f b6 0c 19 84 c9 0f 85 c7 01 00 00 31 d2 <41> f7 34 24 41 89 17 45 89 ec eb 0f e8 c1 77 c7 f9 48 bb 00 00 00
RSP: 0018:ffffc90000007c80 EFLAGS: 00010046
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88807c318400 R08: ffff88807c318400 R09: fffff52001a53601
R10: fffff52001a53601 R11: 1ffff92001a53600 R12: ffff88807c318488
R13: 0000000000000002 R14: 0000000000000000 R15: ffff88807c318434
FS: 00007fc94c4466c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc94c425d58 CR3: 000000001b692000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: b6 0c mov $0xc,%dh
2: 19 84 c9 0f 85 b8 01 sbb %eax,0x1b8850f(%rcx,%rcx,8)
9: 00 00 add %al,(%rax)
b: 03 45 34 add 0x34(%rbp),%eax
e: 4c 8d a5 88 00 00 00 lea 0x88(%rbp),%r12
15: 4c 89 e1 mov %r12,%rcx
18: 48 c1 e9 03 shr $0x3,%rcx
1c: 0f b6 0c 19 movzbl (%rcx,%rbx,1),%ecx
20: 84 c9 test %cl,%cl
22: 0f 85 c7 01 00 00 jne 0x1ef
28: 31 d2 xor %edx,%edx
* 2a: 41 f7 34 24 divl (%r12) <-- trapping instruction
2e: 41 89 17 mov %edx,(%r15)
31: 45 89 ec mov %r13d,%r12d
34: eb 0f jmp 0x45
36: e8 c1 77 c7 f9 call 0xf9c777fc
3b: 48 rex.W
3c: bb .byte 0xbb
3d: 00 00 add %al,(%rax)


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