[syzbot] [comedi?] UBSAN: shift-out-of-bounds in dt2811_attach

[syzbot] [comedi?] UBSAN: shift-out-of-bounds in dt2811_attach

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    93f51579e7df Linux 7.3-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17b45005580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7d012d9c67977ee4
dashboard link: https://syzkaller.appspot.com/bug?extid=a4cedab706d0a8a3f988
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106ff005580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10d054c9580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-93f51579.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/00f02ade84ed/vmlinux-93f51579.xz
kernel image: https://storage.googleapis.com/syzbot-assets/93be890b3b79/bzImage-93f51579.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in drivers/comedi/drivers/dt2811.c:570:31
shift exponent -251 is negative
CPU: 0 UID: 0 PID: 5925 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
 __ubsan_handle_shift_out_of_bounds+0x279/0x2a0 lib/ubsan.c:494
 dt2811_attach.cold+0x19/0x1e drivers/comedi/drivers/dt2811.c:570
 comedi_device_attach+0x40e/0x6b0 drivers/comedi/drivers.c:1101
 do_devconfig_ioctl+0x1b3/0x6d0 drivers/comedi/comedi_fops.c:930
 comedi_unlocked_ioctl+0x860/0x3310 drivers/comedi/comedi_fops.c:2302
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe50959e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffcc3e899c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fe509825fa0 RCX: 00007fe50959e159
RDX: 0000200000000100 RSI: 0000000040946400 RDI: 0000000000000003
RBP: 00007fe50963506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe509825fac R14: 00007fe509825fa0 R15: 00007fe509825fa0
 </TASK>
---[ end trace ]---


---
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[PATCH] test dt2811

[Pei Xiao]

#syz test

---
 drivers/comedi/drivers/dt2811.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/dt2811.c
index 0438b8c90e44..5af2c71de4a2 100644
--- a/drivers/comedi/drivers/dt2811.c
+++ b/drivers/comedi/drivers/dt2811.c
@@ -567,7 +567,7 @@ static int dt2811_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	dt2811_reset(dev);
 
 	/* IRQ's 2,3,5,7 are valid for async command support */
-	if (it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
+	if (it->options[1]>= 0 && it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
 		ret = request_irq(it->options[1], dt2811_interrupt, 0,
 				  dev->board_name, dev);
 		if (ret == 0)
-- 
2.25.1

Re: [syzbot] [comedi?] UBSAN: shift-out-of-bounds in dt2811_attach

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com
Tested-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com

Tested on:

commit:         f0100363 Merge tag 'xfs-fixes-7.3-rc5' of gitolite.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e6f45e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7d012d9c67977ee4
dashboard link: https://syzkaller.appspot.com/bug?extid=a4cedab706d0a8a3f988
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16dfea71580000

Note: testing is done by a robot and is best-effort only.

[PATCH] comedi: dt2811: fix shift-out-of-bounds in IRQ check

[Pei Xiao]

The IRQ number passed via comedi_devconfig->options[1] is a signed int
that comes from userspace.  The check `it->options[1] <= 7` does not
reject negative values, so a negative IRQ number reaches
`BIT(it->options[1])`, which is undefined behavior and triggers a UBSAN
shift-out-of-bounds warning:

  UBSAN: shift-out-of-bounds in drivers/comedi/drivers/dt2811.c:570:31
  shift exponent -251 is negative

Add an explicit lower bound check (`it->options[1] >= 0`) so that only
valid IRQ numbers 0..7 are accepted before the shift.

Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command support for AI subdevice")
Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6ab21240.e548f532.1ca396.0018.GAE@google.com/#R
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
 drivers/comedi/drivers/dt2811.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/dt2811.c
index 0438b8c90e44..53cb17993ae7 100644
--- a/drivers/comedi/drivers/dt2811.c
+++ b/drivers/comedi/drivers/dt2811.c
@@ -567,7 +567,7 @@ static int dt2811_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	dt2811_reset(dev);
 
 	/* IRQ's 2,3,5,7 are valid for async command support */
-	if (it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
+	if (it->options[1] >= 0 && it->options[1] <= 7 && (BIT(it->options[1]) & 0xac)) {
 		ret = request_irq(it->options[1], dt2811_interrupt, 0,
 				  dev->board_name, dev);
 		if (ret == 0)
-- 
2.25.1

Re: [PATCH] comedi: dt2811: fix shift-out-of-bounds in IRQ check

[Ian Abbott]

On 2026-09-22 08:16, Pei Xiao wrote:
> The IRQ number passed via comedi_devconfig->options[1] is a signed int
> that comes from userspace.  The check `it->options[1] <= 7` does not
> reject negative values, so a negative IRQ number reaches
> `BIT(it->options[1])`, which is undefined behavior and triggers a UBSAN
> shift-out-of-bounds warning:
> 
>    UBSAN: shift-out-of-bounds in drivers/comedi/drivers/dt2811.c:570:31
>    shift exponent -251 is negative
> 
> Add an explicit lower bound check (`it->options[1] >= 0`) so that only
> valid IRQ numbers 0..7 are accepted before the shift.
> 
> Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command support for AI subdevice")
> Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6ab21240.e548f532.1ca396.0018.GAE@google.com/#R
> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
> ---
>   drivers/comedi/drivers/dt2811.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/dt2811.c
> index 0438b8c90e44..53cb17993ae7 100644
> --- a/drivers/comedi/drivers/dt2811.c
> +++ b/drivers/comedi/drivers/dt2811.c
> @@ -567,7 +567,7 @@ static int dt2811_attach(struct comedi_device *dev, struct comedi_devconfig *it)
>   	dt2811_reset(dev);
>   
>   	/* IRQ's 2,3,5,7 are valid for async command support */
> -	if (it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
> +	if (it->options[1] >= 0 && it->options[1] <= 7 && (BIT(it->options[1]) & 0xac)) {
>   		ret = request_irq(it->options[1], dt2811_interrupt, 0,
>   				  dev->board_name, dev);
>   		if (ret == 0)

Looks good, thanks!

Please could you resend and Cc: Greg Kroah-Hartman 
<gregkh@linuxfoundation.org> ?  Thanks!

-- 
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company  )=-
-=( registered in England & Wales.  Regd. number: 02862268.  )=-
-=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=-
-=( Bird Hall Lane, STOCKPORT, SK3 0XA, UK. || www.mev.co.uk )=-

Re: [PATCH] comedi: dt2811: fix shift-out-of-bounds in IRQ check

[Pei Xiao]

在 2026/9/22 17:11, Ian Abbott 写道:
> On 2026-09-22 08:16, Pei Xiao wrote:
>> The IRQ number passed via comedi_devconfig->options[1] is a signed int
>> that comes from userspace.  The check `it->options[1] <= 7` does not
>> reject negative values, so a negative IRQ number reaches
>> `BIT(it->options[1])`, which is undefined behavior and triggers a UBSAN
>> shift-out-of-bounds warning:
>>
>>    UBSAN: shift-out-of-bounds in drivers/comedi/drivers/dt2811.c:570:31
>>    shift exponent -251 is negative
>>
>> Add an explicit lower bound check (`it->options[1] >= 0`) so that only
>> valid IRQ numbers 0..7 are accepted before the shift.
>>
>> Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command
>> support for AI subdevice")
>> Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com
>> Closes: https://lore.kernel.org/
>> all/6ab21240.e548f532.1ca396.0018.GAE@google.com/#R
>> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
>> ---
>>   drivers/comedi/drivers/dt2811.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/
>> dt2811.c
>> index 0438b8c90e44..53cb17993ae7 100644
>> --- a/drivers/comedi/drivers/dt2811.c
>> +++ b/drivers/comedi/drivers/dt2811.c
>> @@ -567,7 +567,7 @@ static int dt2811_attach(struct comedi_device
>> *dev, struct comedi_devconfig *it)
>>       dt2811_reset(dev);
>>         /* IRQ's 2,3,5,7 are valid for async command support */
>> -    if (it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
>> +    if (it->options[1] >= 0 && it->options[1] <= 7 && (BIT(it-
>> >options[1]) & 0xac)) {
>>           ret = request_irq(it->options[1], dt2811_interrupt, 0,
>>                     dev->board_name, dev);
>>           if (ret == 0)
> 
> Looks good, thanks!
> 
> Please could you resend and Cc: Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> ?  Thanks!
ok. Thanks!

Pei.>

[PATCH] comedi: dt2811: fix shift-out-of-bounds in IRQ check

[Pei Xiao]

The IRQ number passed via comedi_devconfig->options[1] is a signed int
that comes from userspace.  The check `it->options[1] <= 7` does not
reject negative values, so a negative IRQ number reaches
`BIT(it->options[1])`, which is undefined behavior and triggers a UBSAN
shift-out-of-bounds warning:

  UBSAN: shift-out-of-bounds in drivers/comedi/drivers/dt2811.c:570:31
  shift exponent -251 is negative

Add an explicit lower bound check (`it->options[1] >= 0`) so that only
valid IRQ numbers 0..7 are accepted before the shift.

Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command support for AI subdevice")
Reported-by: syzbot+a4cedab706d0a8a3f988@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6ab21240.e548f532.1ca396.0018.GAE@google.com/#R
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
 drivers/comedi/drivers/dt2811.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/dt2811.c
index 0438b8c90e44..53cb17993ae7 100644
--- a/drivers/comedi/drivers/dt2811.c
+++ b/drivers/comedi/drivers/dt2811.c
@@ -567,7 +567,7 @@ static int dt2811_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	dt2811_reset(dev);
 
 	/* IRQ's 2,3,5,7 are valid for async command support */
-	if (it->options[1] <= 7  && (BIT(it->options[1]) & 0xac)) {
+	if (it->options[1] >= 0 && it->options[1] <= 7 && (BIT(it->options[1]) & 0xac)) {
 		ret = request_irq(it->options[1], dt2811_interrupt, 0,
 				  dev->board_name, dev);
 		if (ret == 0)
-- 
2.25.1