[Nouveau] [PATCH] nouveau/u_memcpya: fix NULL vs error pointer bug

[Danilo Krummrich]

On 9/16/23 16:26, Dan Carpenter wrote:
> On Sat, Sep 16, 2023 at 05:24:04PM +0300, Dan Carpenter wrote:
>> On Sat, Sep 16, 2023 at 01:41:43AM +0200, Danilo Krummrich wrote:
>>> Hi Dan,
>>>
>>> On 9/15/23 14:59, Dan Carpenter wrote:
>>>> The u_memcpya() function is supposed to return error pointers on
>>>> error.  Returning NULL will lead to an Oops.
>>>>
>>>> Fixes: 68132cc6d1bc ("nouveau/u_memcpya: use vmemdup_user")
>>>> Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
>>>> ---
>>>>    drivers/gpu/drm/nouveau/nouveau_drv.h | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
>>>> index 3666a7403e47..52a708a98915 100644
>>>> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
>>>> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
>>>> @@ -193,7 +193,7 @@ u_memcpya(uint64_t user, unsigned int nmemb, unsigned int size)
>>>>    	size_t bytes;
>>>>    	if (unlikely(check_mul_overflow(nmemb, size, &bytes)))
>>>> -		return NULL;
>>>> +		return ERR_PTR(-ENOMEM);
>>>
>>> I plan to replace this function with an upcoming vmemdup_array_user() helper,
>>> which returns -EOVERFLOW instead, hence mind using that?
>>>
>>> Unless you disagree, no need to resubmit the patch, I can change it
>>> before applying the patch.
>>
>> Generally, I would say that ENOMEM is the correct error code.  I feel
>> like someone thinks EOVERFLOW means integer overflow and that's not
>> correct.  I means like if you pass a number higher than INT_MAX to
>> kstroint().
> 
> The most common error code for integer overflows is EINVAL because the
> user passed invalid data.

I totally agree with that, and my choice would have been EINVAL as well. It's just
that it seems (v)memdup_array_user() [1] goes with that and hence I'd just go along.

[1] https://lore.kernel.org/lkml/93001a9f3f101be0f374080090f9c32df73ca773.1694202430.git.pstanner@redhat.com/

> 
> regards,
> dan carpenter
>