linux-kernel - [syzbot] [kernel?] divide error in comedi_buf_write

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Message-ID: <686ea917.050a0220.385921.0014.GAE@google.com>
Date: Wed, 09 Jul 2025 10:38:31 -0700
From: syzbot <syzbot+f6c3c066162d2c43a66c@...kaller.appspotmail.com>
To: abbotti@....co.uk, hsweeten@...ionengravers.com, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [kernel?] divide error in comedi_buf_write_free

Hello,

syzbot found the following issue on:

HEAD commit:    58ba80c47402 Add linux-next specific files for 20250708
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15e9ea8c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=16e0d64c5a66f7ca
dashboard link: https://syzkaller.appspot.com/bug?extid=f6c3c066162d2c43a66c
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/27011e78b607/disk-58ba80c4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a3b2e0bf7f86/vmlinux-58ba80c4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/512dbc2f3800/bzImage-58ba80c4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f6c3c066162d2c43a66c@...kaller.appspotmail.com

Oops: divide error: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.16.0-rc5-next-20250708-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:comedi_buf_munge drivers/comedi/comedi_buf.c:347 [inline]
RIP: 0010:comedi_buf_write_free+0x3c8/0x7e0 drivers/comedi/comedi_buf.c:391
Code: 41 03 45 00 48 8b 4c 24 78 42 0f b6 0c 21 84 c9 4c 8b bc 24 90 00 00 00 44 8b 74 24 54 0f 85 02 01 00 00 31 d2 48 8b 4c 24 30 <f7> 31 41 89 55 00 48 8b 44 24 70 42 0f b6 04 20 84 c0 0f 85 09 01
RSP: 0018:ffffc90000007bd8 EFLAGS: 00010046
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: ffff888030a20880
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff88806b192000
RBP: 0000000000000002 R08: 0000000000000000 R09: 00000000000000ff
R10: dffffc0000000000 R11: ffffffff88e91b20 R12: dffffc0000000000
R13: ffff888030a20838 R14: 0000000000000000 R15: ffff888030a20800
FS:  0000000000000000(0000) GS:ffff888125bd7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007faab2ff5f98 CR3: 0000000033708000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 comedi_buf_write_samples+0x369/0x5a0 drivers/comedi/comedi_buf.c:602
 das16m1_handler+0x213/0x4b0 drivers/comedi/drivers/das16m1.c:413
 das16m1_interrupt+0xaf/0x180 drivers/comedi/drivers/das16m1.c:470
 __handle_irq_event_percpu+0x289/0x980 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
 handle_irq_event+0x8b/0x1e0 kernel/irq/handle.c:210
 handle_edge_irq+0x267/0x9c0 kernel/irq/chip.c:797
 generic_handle_irq_desc include/linux/irqdesc.h:173 [inline]
 handle_irq arch/x86/kernel/irq.c:254 [inline]
 call_irq_handler arch/x86/kernel/irq.c:266 [inline]
 __common_interrupt+0x140/0x250 arch/x86/kernel/irq.c:292
 common_interrupt+0xb6/0xe0 arch/x86/kernel/irq.c:285
 </IRQ>
 <TASK>
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:693
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d c3 ec 0f 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff8de07d80 EFLAGS: 000002c6
RAX: 709f8e7c1b77cc00 RBX: ffffffff8196cd28 RCX: 709f8e7c1b77cc00
RDX: 0000000000000001 RSI: ffffffff8d9aefc8 RDI: ffffffff8be33740
RBP: ffffffff8de07ea8 R08: ffff8880b8632f5b R09: 1ffff110170c65eb
R10: dffffc0000000000 R11: ffffed10170c65ec R12: ffffffff8fa35430
R13: 0000000000000000 R14: 0000000000000000 R15: 1ffffffff1bd2a50
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:757
 default_idle_call+0x74/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:190 [inline]
 do_idle+0x1e8/0x510 kernel/sched/idle.c:330
 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:428
 rest_init+0x2de/0x300 init/main.c:744
 start_kernel+0x47d/0x500 init/main.c:1097
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:307
 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:288
 common_startup_64+0x13e/0x147
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:comedi_buf_munge drivers/comedi/comedi_buf.c:347 [inline]
RIP: 0010:comedi_buf_write_free+0x3c8/0x7e0 drivers/comedi/comedi_buf.c:391
Code: 41 03 45 00 48 8b 4c 24 78 42 0f b6 0c 21 84 c9 4c 8b bc 24 90 00 00 00 44 8b 74 24 54 0f 85 02 01 00 00 31 d2 48 8b 4c 24 30 <f7> 31 41 89 55 00 48 8b 44 24 70 42 0f b6 04 20 84 c0 0f 85 09 01
RSP: 0018:ffffc90000007bd8 EFLAGS: 00010046
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: ffff888030a20880
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff88806b192000
RBP: 0000000000000002 R08: 0000000000000000 R09: 00000000000000ff
R10: dffffc0000000000 R11: ffffffff88e91b20 R12: dffffc0000000000
R13: ffff888030a20838 R14: 0000000000000000 R15: ffff888030a20800
FS:  0000000000000000(0000) GS:ffff888125bd7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007faab2ff5f98 CR3: 0000000033708000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	41 03 45 00          	add    0x0(%r13),%eax
   4:	48 8b 4c 24 78       	mov    0x78(%rsp),%rcx
   9:	42 0f b6 0c 21       	movzbl (%rcx,%r12,1),%ecx
   e:	84 c9                	test   %cl,%cl
  10:	4c 8b bc 24 90 00 00 	mov    0x90(%rsp),%r15
  17:	00
  18:	44 8b 74 24 54       	mov    0x54(%rsp),%r14d
  1d:	0f 85 02 01 00 00    	jne    0x125
  23:	31 d2                	xor    %edx,%edx
  25:	48 8b 4c 24 30       	mov    0x30(%rsp),%rcx
* 2a:	f7 31                	divl   (%rcx) <-- trapping instruction
  2c:	41 89 55 00          	mov    %edx,0x0(%r13)
  30:	48 8b 44 24 70       	mov    0x70(%rsp),%rax
  35:	42 0f b6 04 20       	movzbl (%rax,%r12,1),%eax
  3a:	84 c0                	test   %al,%al
  3c:	0f                   	.byte 0xf
  3d:	85 09                	test   %ecx,(%rcx)
  3f:	01                   	.byte 0x1


---
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