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

Pei Xiao posted 1 patch 2 days, 8 hours ago 
drivers/comedi/drivers/dt2811.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[PATCH] comedi: dt2811: fix shift-out-of-bounds in IRQ check
Posted by Pei Xiao 2 days, 8 hours ago 
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
Posted by Ian Abbott 1 day, 6 hours ago 
On 2026-09-22 10:19, 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!

Reviewed-by: Ian Abbott <abbotti@mev.co.uk>

-- 
-=( 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
Posted by Ian Abbott 2 days, 6 hours ago 
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
Posted by Pei Xiao 2 days, 6 hours ago 

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.>

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