Re: [igt-dev] [PATCH i-g-t v2] lib/igt_kms: Fix memory corruption

[Daniel Stone <daniels@collabora.com>]

Hi Vignesh,

On 06/11/2023 02:40, Vignesh Raman wrote:
> Hi Daniel,
>
> On 27/10/23 22:07, Daniel Stone wrote:
>> Hi Vignesh,
>>
>> On 27/10/2023 15:40, Vignesh Raman wrote:
>>> In crosvm, the kernel reports 16 for count_crtcs, which exceeds
>>> IGT_MAX_PIPES set to 8. The function igt_display_require allocates
>>> memory for IGT_MAX_PIPES members of igt_pipe_t structures, but then
>>> writes into it based on the count_crtcs reported by the kernel,
>>> resulting in memory corruption.
>>
>> To make this robust against future changes (32 CRTCs seems totally 
>> fanciful, but so did 16 a while ago), this needs to also be robust 
>> against count_crtcs exceeding IGT_NUM_PIPES, along the lines of your 
>> previous change.
>
> Yes, I agree to make the code robust against potential changes in the 
> future. We can set IGT_MAX_PIPES to 32. I will send an updated patch.

What I mean is to make sure that the code cannot access out of bounds, 
regardless of the number. We can set IGT_MAX_PIPES to 32 but then 
someone will hit the same failure when there are more CRTCs than that.

The way to do this would probably be to igt_require() that count_crtcs 
does not exceed IGT_MAX_PIPES, in all the paths where we access the 
crtcs array. There is no need to bump the limit to 32 until it's required.

Cheers,
Daniel