Re: [PATCH] drm/scheduler: Fix UAF in drm_sched_fence_get_timeline_name

Luben Tuikov
2023-04-05T18:10:09Z

On 2023-04-05 12:34, Asahi Lina wrote:
> A signaled scheduler fence can outlive its scheduler, since fences are
> independently reference counted. Therefore, we can't reference the
> scheduler in the get_timeline_name() implementation.
>
> Fixes oopses on `cat /sys/kernel/debug/dma_buf/bufinfo` when shared
> dma-bufs reference fences from GPU schedulers that no longer exist.
>
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> ---

Thanks for fixing this. If there's no objections, I'll add my tag
and I'll push this tomorrow. I think this should go in through
drm-misc-fixes and drm-misc-next.

Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>

Regards,
Luben

> drivers/gpu/drm/scheduler/sched_entity.c | 7 ++++++-
> drivers/gpu/drm/scheduler/sched_fence.c | 4 +++-
> include/drm/gpu_scheduler.h | 5 +++++
> 3 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 15d04a0ec623..8b3b949b2ce8 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -368,7 +368,12 @@ static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
>
> /*
> * Fence is from the same scheduler, only need to wait for
> - * it to be scheduled
> + * it to be scheduled.
> + *
> + * Note: s_fence->sched could have been freed and reallocated
> + * as another scheduler. This false positive case is okay, as if
> + * the old scheduler was freed all of its jobs must have
> + * signaled their completion fences.
> */
> fence = dma_fence_get(&s_fence->scheduled);
> dma_fence_put(entity->dependency);
> diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
> index 7fd869520ef2..33b145dfa38c 100644
> --- a/drivers/gpu/drm/scheduler/sched_fence.c
> +++ b/drivers/gpu/drm/scheduler/sched_fence.c
> @@ -66,7 +66,7 @@ static const char *drm_sched_fence_get_driver_name(struct dma_fence *fence)
> static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f)
> {
> struct drm_sched_fence *fence = to_drm_sched_fence(f);
> - return (const char *)fence->sched->name;
> + return (const char *)fence->sched_name;
> }
>
> static void drm_sched_fence_free_rcu(struct rcu_head *rcu)
> @@ -168,6 +168,8 @@ void drm_sched_fence_init(struct drm_sched_fence *fence,
> unsigned seq;
>
> fence->sched = entity->rq->sched;
> + strlcpy(fence->sched_name, entity->rq->sched->name,
> + sizeof(fence->sched_name));
> seq = atomic_inc_return(&entity->fence_seq);
> dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled,
> &fence->lock, entity->fence_context, seq);
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index 9db9e5e504ee..49f019731891 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -295,6 +295,11 @@ struct drm_sched_fence {
> * @lock: the lock used by the scheduled and the finished fences.
> */
> spinlock_t lock;
> + /**
> + * @sched_name: the name of the scheduler that owns this fence. We
> + * keep a copy here since fences can outlive their scheduler.
> + */
> + char sched_name[16];
> /**
> * @owner: job owner for debugging
> */
>
> ---
> base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6
> change-id: 20230406-scheduler-uaf-1-994ec34cac93
>
> Thank you,
> ~~ Lina
>