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

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Message-ID: <68d98bd1.a00a0220.102ee.002f.GAE@google.com>
Date: Sun, 28 Sep 2025 12:26:09 -0700
From: syzbot <syzbot+c7e121cdcbe0b0bce98e@...kaller.appspotmail.com>
To: xandfury@...il.com
Cc: xandfury@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] UBSAN: shift-out-of-bounds in comedi_device_attach

> syzbot <syzbot+c7e121cdcbe0b0bce98e@...kaller.appspotmail.com> writes:
>
>> 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
>>
>>
>> —
>> This report is generated by a bot. It may contain errors.
>> See <https://goo.gl/tpsmEJ> for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@...glegroups.com.
>>
>> syzbot will keep track of this issue. See:
>> <https://goo.gl/tpsmEJ#status> for how to communicate with syzbot.
>>
>> If the report is already addressed, let syzbot know by replying with:
>> #syz fix: exact-commit-title
>>
>> If you want to overwrite report’s subsystems, reply with:
>> #syz set subsystems: new-subsystem
>> (See the list of subsystem names on the web dashboard)
>>
>> If the report is a duplicate of another one, reply with:
>> #syz dup: exact-subject-of-another-report
>>
>> If you want to undo deduplication, reply with:
>> #syz undup
>
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

This crash does not have a reproducer. I cannot test it.