Re: [PATCH] media: staging: atomisp: fix a potential missing-check bug

From: Wenwen Wang
Date: Tue May 08 2018 - 09:05:42 EST

On Tue, May 8, 2018 at 7:16 AM, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> On Wed, May 02, 2018 at 05:38:49PM -0500, Wenwen Wang wrote:
>> At the end of atomisp_subdev_set_selection(), the function
>> atomisp_subdev_get_rect() is invoked to get the pointer to v4l2_rect. Since
>> this function may return a NULL pointer, it is firstly invoked to check
>> the returned pointer. If the returned pointer is not NULL, then the
>> function is invoked again to obtain the pointer and the memory content
>> at the location of the returned pointer is copied to the memory location of
>> r. In most cases, the pointers returned by the two invocations are same.
>> However, given that the pointer returned by the function
>> atomisp_subdev_get_rect() is not a constant, it is possible that the two
>> invocations return two different pointers. For example, another thread may
>> race to modify the related pointers during the two invocations.
> You're assuming a very serious race condition exists.
>> In that
>> case, even if the first returned pointer is not null, the second returned
>> pointer might be null, which will cause issues such as null pointer
>> dereference.
> And then complaining that if a really serious bug exists then this very
> minor bug would exist too... If there were really a race condition like
> that then we'd want to fix it instead. In other words, this is not a
> real life bug fix.
> But it would be fine as a readability or static checker fix so that's
> fine.

Thanks for your response. From the performance perspective, this bug
should also be fixed, as the second invocation is redundant if it is
expected to return a same pointer as the first one.