linux-kernel - [syzbot] [kernel?] UBSAN: shift-out-of-bounds in comedi_device

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Message-ID: <6878b37c.a70a0220.693ce.0041.GAE@google.com>
Date: Thu, 17 Jul 2025 01:25:32 -0700
From: syzbot <syzbot+c7e121cdcbe0b0bce98e@...kaller.appspotmail.com>
To: abbotti@....co.uk, hsweeten@...ionengravers.com, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [kernel?] UBSAN: shift-out-of-bounds in comedi_device_attach

Hello,

syzbot found the following issue on:

HEAD commit:    155a3c003e55 Merge tag 'for-6.16/dm-fixes-2' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11196382580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=693e2f5eea496864
dashboard link: https://syzkaller.appspot.com/bug?extid=c7e121cdcbe0b0bce98e
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-155a3c00.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a8464683662c/vmlinux-155a3c00.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e74dc5d462a7/bzImage-155a3c00.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c7e121cdcbe0b0bce98e@...kaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in drivers/comedi/drivers/pcl812.c:1152:10
shift exponent 1029 is too large for 32-bit type 'int'
CPU: 3 UID: 0 PID: 6168 Comm: syz.0.33 Not tainted 6.16.0-rc6-syzkaller-00002-g155a3c003e55 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:233 [inline]
 __ubsan_handle_shift_out_of_bounds+0x27f/0x420 lib/ubsan.c:494
 comedi_device_attach+0x3b3/0x900 drivers/comedi/drivers.c:996
 do_devconfig_ioctl+0x1a7/0x580 drivers/comedi/comedi_fops.c:855
 comedi_unlocked_ioctl+0x15bb/0x2e90 drivers/comedi/comedi_fops.c:2136
 comedi_compat_ioctl+0x1d0/0x910 drivers/comedi/comedi_fops.c:3201
 __do_compat_sys_ioctl fs/ioctl.c:1005 [inline]
 __se_compat_sys_ioctl fs/ioctl.c:948 [inline]
 __ia32_compat_sys_ioctl+0x23f/0x370 fs/ioctl.c:948
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7f15579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f503655c EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000040946400
RDX: 00000000800000c0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
---[ end trace ]---
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	10 06                	adc    %al,(%rsi)
   2:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
   6:	10 07                	adc    %al,(%rdi)
   8:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
   c:	10 08                	adc    %cl,(%rax)
   e:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1e:	00 51 52             	add    %dl,0x52(%rcx)
  21:	55                   	push   %rbp
  22:	89 e5                	mov    %esp,%ebp
  24:	0f 34                	sysenter
  26:	cd 80                	int    $0x80
* 28:	5d                   	pop    %rbp <-- trapping instruction
  29:	5a                   	pop    %rdx
  2a:	59                   	pop    %rcx
  2b:	c3                   	ret
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
  37:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi


---
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