[PATCH 2/2] drm: Fix potential null-ptr-deref in drm_vblank_destroy_worker()

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude at redhat.com>

On Tue, 2022-11-01 at 15:07 +0800, Shang XiaoJing wrote:
> drm_vblank_init() call drmm_add_action_or_reset() with
> drm_vblank_init_release() as action. If __drmm_add_action() failed, will
> directly call drm_vblank_init_release() with the vblank whose worker is
> NULL. As the resule, a null-ptr-deref will happen in
> kthread_destroy_worker(). Add the NULL check before calling
> drm_vblank_destroy_worker().
> 
> BUG: null-ptr-deref
> KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
> CPU: 5 PID: 961 Comm: modprobe Not tainted 6.0.0-11331-gd465bff130bf-dirty
> RIP: 0010:kthread_destroy_worker+0x25/0xb0
>   Call Trace:
>     <TASK>
>     drm_vblank_init_release+0x124/0x220 [drm]
>     ? drm_crtc_vblank_restore+0x8b0/0x8b0 [drm]
>     __drmm_add_action_or_reset+0x41/0x50 [drm]
>     drm_vblank_init+0x282/0x310 [drm]
>     vkms_init+0x35f/0x1000 [vkms]
>     ? 0xffffffffc4508000
>     ? lock_is_held_type+0xd7/0x130
>     ? __kmem_cache_alloc_node+0x1c2/0x2b0
>     ? lock_is_held_type+0xd7/0x130
>     ? 0xffffffffc4508000
>     do_one_initcall+0xd0/0x4f0
>     ...
>     do_syscall_64+0x35/0x80
>     entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> Fixes: 5e6c2b4f9161 ("drm/vblank: Add vblank works")
> Signed-off-by: Shang XiaoJing <shangxiaojing at huawei.com>
> ---
>  drivers/gpu/drm/drm_internal.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 7bb98e6a446d..5ea5e260118c 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -104,7 +104,8 @@ static inline void drm_vblank_flush_worker(struct drm_vblank_crtc *vblank)
>  
>  static inline void drm_vblank_destroy_worker(struct drm_vblank_crtc *vblank)
>  {
> -	kthread_destroy_worker(vblank->worker);
> +	if (vblank->worker)
> +		kthread_destroy_worker(vblank->worker);
>  }
>  
>  int drm_vblank_worker_init(struct drm_vblank_crtc *vblank);

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat