[PATCH] comedi: zero-init data in do_insn_ioctl

[PATCH] comedi: zero-init data in do_insn_ioctl

[Arnaud Lecomte]

KMSAN reported a kernel-infoleak when copying instruction data back to
userspace in do_insnlist_ioctl(). The issue occurs because allocated
memory buffers weren't properly initialized (not
zero initialized)  before being copied to
userspace, potentially leaking kernel memory.

Reported-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
Tested-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
---
 drivers/comedi/comedi_fops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
index c83fd14dd7ad..15fee829d14c 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -1636,7 +1636,7 @@ static int do_insn_ioctl(struct comedi_device *dev,
 		n_data = MAX_SAMPLES;
 	}
 
-	data = kmalloc_array(n_data, sizeof(unsigned int), GFP_KERNEL);
+	data = kcalloc(n_data, sizeof(unsigned int), GFP_KERNEL);
 	if (!data) {
 		ret = -ENOMEM;
 		goto error;
-- 
2.43.0

Re: [PATCH] comedi: zero-init data in do_insn_ioctl

[Ian Abbott]

On 24/07/2025 22:04, Arnaud Lecomte wrote:
> KMSAN reported a kernel-infoleak when copying instruction data back to
> userspace in do_insnlist_ioctl(). The issue occurs because allocated
> memory buffers weren't properly initialized (not
> zero initialized)  before being copied to
> userspace, potentially leaking kernel memory.
> 
> Reported-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
> Tested-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
> ---
>   drivers/comedi/comedi_fops.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
> index c83fd14dd7ad..15fee829d14c 100644
> --- a/drivers/comedi/comedi_fops.c
> +++ b/drivers/comedi/comedi_fops.c
> @@ -1636,7 +1636,7 @@ static int do_insn_ioctl(struct comedi_device *dev,
>   		n_data = MAX_SAMPLES;
>   	}
>   
> -	data = kmalloc_array(n_data, sizeof(unsigned int), GFP_KERNEL);
> +	data = kcalloc(n_data, sizeof(unsigned int), GFP_KERNEL);
>   	if (!data) {
>   		ret = -ENOMEM;
>   		goto error;

I thought my commit 46d8c744136c ("comedi: Fix initialization of data 
for instructions that write to subdevice" would have fixed this as long 
as all the driver code was playing nicely, but it seems I was mistaken.

I don't think it is necessary to use kcalloc().  The buffer already gets 
initialized (partly by `copy_from_user()`) when `insn->insn & 
INSN_MASK_WRITE` is non-zero, so it just needs to be initialized when 
`insn->insn & INSN_MASK_WRITE` is zero too.

There is nearly identical code in `do_insnlist_ioctl()` that needs 
fixing, so it would be better to fix both at the same time.

-- 
-=( 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: zero-init data in do_insn_ioctl

[Lecomte, Arnaud]

Hi Ian,
Thanks for the feedback, I can send the revision of the patch by the end 
of the day if it is fine for you.


On 25/07/2025 10:41, Ian Abbott wrote:
> On 24/07/2025 22:04, Arnaud Lecomte wrote:
>> KMSAN reported a kernel-infoleak when copying instruction data back to
>> userspace in do_insnlist_ioctl(). The issue occurs because allocated
>> memory buffers weren't properly initialized (not
>> zero initialized)  before being copied to
>> userspace, potentially leaking kernel memory.
>>
>> Reported-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
>> Tested-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
>> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
>> ---
>>   drivers/comedi/comedi_fops.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
>> index c83fd14dd7ad..15fee829d14c 100644
>> --- a/drivers/comedi/comedi_fops.c
>> +++ b/drivers/comedi/comedi_fops.c
>> @@ -1636,7 +1636,7 @@ static int do_insn_ioctl(struct comedi_device 
>> *dev,
>>           n_data = MAX_SAMPLES;
>>       }
>>   -    data = kmalloc_array(n_data, sizeof(unsigned int), GFP_KERNEL);
>> +    data = kcalloc(n_data, sizeof(unsigned int), GFP_KERNEL);
>>       if (!data) {
>>           ret = -ENOMEM;
>>           goto error;
>
> I thought my commit 46d8c744136c ("comedi: Fix initialization of data 
> for instructions that write to subdevice" would have fixed this as 
> long as all the driver code was playing nicely, but it seems I was 
> mistaken.
>
> I don't think it is necessary to use kcalloc().  The buffer already 
> gets initialized (partly by `copy_from_user()`) when `insn->insn & 
> INSN_MASK_WRITE` is non-zero, so it just needs to be initialized when 
> `insn->insn & INSN_MASK_WRITE` is zero too.
>
> There is nearly identical code in `do_insnlist_ioctl()` that needs 
> fixing, so it would be better to fix both at the same time.
>

Re: [PATCH] comedi: zero-init data in do_insn_ioctl

[Ian Abbott]

On 25/07/2025 10:43, Lecomte, Arnaud wrote:
> Hi Ian,
> Thanks for the feedback, I can send the revision of the patch by the end 
> of the day if it is fine for you.

Actually, I'm just building a (hopefully) fixed version at the moment. 
I'll add you to the Cc list for it.

> On 25/07/2025 10:41, Ian Abbott wrote:
>> On 24/07/2025 22:04, Arnaud Lecomte wrote:
>>> KMSAN reported a kernel-infoleak when copying instruction data back to
>>> userspace in do_insnlist_ioctl(). The issue occurs because allocated
>>> memory buffers weren't properly initialized (not
>>> zero initialized)  before being copied to
>>> userspace, potentially leaking kernel memory.
>>>
>>> Reported-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
>>> Tested-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
>>> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
>>> ---
>>>   drivers/comedi/comedi_fops.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
>>> index c83fd14dd7ad..15fee829d14c 100644
>>> --- a/drivers/comedi/comedi_fops.c
>>> +++ b/drivers/comedi/comedi_fops.c
>>> @@ -1636,7 +1636,7 @@ static int do_insn_ioctl(struct comedi_device 
>>> *dev,
>>>           n_data = MAX_SAMPLES;
>>>       }
>>>   -    data = kmalloc_array(n_data, sizeof(unsigned int), GFP_KERNEL);
>>> +    data = kcalloc(n_data, sizeof(unsigned int), GFP_KERNEL);
>>>       if (!data) {
>>>           ret = -ENOMEM;
>>>           goto error;
>>
>> I thought my commit 46d8c744136c ("comedi: Fix initialization of data 
>> for instructions that write to subdevice" would have fixed this as 
>> long as all the driver code was playing nicely, but it seems I was 
>> mistaken.
>>
>> I don't think it is necessary to use kcalloc().  The buffer already 
>> gets initialized (partly by `copy_from_user()`) when `insn->insn & 
>> INSN_MASK_WRITE` is non-zero, so it just needs to be initialized when 
>> `insn->insn & INSN_MASK_WRITE` is zero too.
>>
>> There is nearly identical code in `do_insnlist_ioctl()` that needs 
>> fixing, so it would be better to fix both at the same time.
>>


-- 
-=( 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: zero-init data in do_insn_ioctl

[Lecomte, Arnaud]

Thanks Ian !
Keep me in touch on how it is going or if you need my help at any moment.

On 25/07/2025 11:04, Ian Abbott wrote:
>
> Actually, I'm just building a (hopefully) fixed version at the moment. 
> I'll add you to the Cc list for it.