Re: [PATCH] drm/sched: Fix UB pointer dereference

["Christian König" <christian.koenig@amd.com>]

Am 27.08.24 um 10:39 schrieb Danilo Krummrich:
> On 8/27/24 9:45 AM, Philipp Stanner wrote:
>> In drm_sched_job_init(), commit 56e449603f0a ("drm/sched: Convert the
>> GPU scheduler to variable number of run-queues") implemented a call to
>> drm_err(), which uses the job's scheduler pointer as a parameter.
>> job->sched, however, is not yet valid as it gets set by
>> drm_sched_job_arm(), which is always called after drm_sched_job_init().
>>
>> Since the scheduler code has no control over how the API-User has
>> allocated or set 'job', the pointer's dereference is undefined behavior.
>>
>> Fix the UB by replacing drm_err() with pr_err().
>>
>> Cc: <stable@vger.kernel.org>    # 6.7+
>> Fixes: 56e449603f0a ("drm/sched: Convert the GPU scheduler to 
>> variable number of run-queues")
>> Reported-by: Danilo Krummrich <dakr@redhat.com>
>> Closes: 
>> https://lore.kernel.org/lkml/20231108022716.15250-1-dakr@redhat.com/
>> Signed-off-by: Philipp Stanner <pstanner@redhat.com>
>> ---
>>   drivers/gpu/drm/scheduler/sched_main.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c 
>> b/drivers/gpu/drm/scheduler/sched_main.c
>> index 7e90c9f95611..356c30fa24a8 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -797,7 +797,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
>>            * or worse--a blank screen--leave a trail in the
>>            * logs, so this can be debugged easier.
>>            */
>> -        drm_err(job->sched, "%s: entity has no rq!\n", __func__);
>> +        pr_err("*ERROR* %s: entity has no rq!\n", __func__);
>
> I don't think the "*ERROR*" string is necessary, it's pr_err() already.

Good point. I will remove that and also add a comment why drm_err won't 
work here before pushing it to drm-misc-fixes.

Thanks,
Christian.

>
> Otherwise,
>
> Acked-by: Danilo Krummrich <dakr@kernel.org>
>
>>           return -ENOENT;
>>       }