[Intel-gfx] Potential NULL pointer dereference in intel_crt_get_edid

[Rodrigo Vivi]

Hi Shaobo,

n Mon, Mar 18, 2019 at 05:01:10PM -0600, Shaobo He wrote:
> Hello everyone,
> 
> My name is Shaobo He and I am a graduate student at University of Utah. I am
> using a static analysis tool to search for null pointer dereferences and
> came across a potentially invalid memory access in the file
> drivers/gpu/drm/i915/intel_crt.c: in function `intel_crt_detect_ddc`,
> function `intel_gmbus_get_adapter` can return a NULL pointer which is

if this happens we've done a terrible job on defining the platform...

> dereferenced by the call to `drm_get_edid` or `intel_gmbus_is_forced_bit`.

but it seems you are right... this will reach i2c_transfer in the end
and it will break everything after we gave the Warning...

> It seems that the return value of `intel_gmbus_get_adapter` is never
> NULL-checked. If so, it would be better to replace the branch to return a
> NULL pointer with something like `BUG_ON`.

what about just adding if (!i2c) return false
instead of BUG.

We already have the WARN to debug if this case ever happens.

Thanks,
Rodrigo.

> 
> Please let me know if it makes sense. I am looking forward to your reply.
> 
> Best,
> Shaobo