[PATCH] drm/amd/display: Fix some use after free bugs

[Bhawanpreet Lakha]

Reviewed-by: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>

On 2020-02-05 1:38 p.m., Dan Carpenter wrote:
> These frees need to be re-ordered so that we don't dereference "hdcp_work"
> right after it's freed.  Also in hdcp_create_workqueue() there is a
> problem that "hdcp_work" can be NULL if the allocation fails so it would
> lead to a NULL dereference in the cleanup code.
>
> Fixes: 9aeb8a134a0a ("drm/amd/display: Add sysfs interface for set/get srm")
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> ---
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c
> index 1768a33b1dc3..f3330df782a4 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c
> @@ -380,9 +380,9 @@ void hdcp_destroy(struct hdcp_workqueue *hdcp_work)
>   		cancel_delayed_work_sync(&hdcp_work[i].watchdog_timer_dwork);
>   	}
>   
> -	kfree(hdcp_work);
>   	kfree(hdcp_work->srm);
>   	kfree(hdcp_work->srm_temp);
> +	kfree(hdcp_work);
>   }
>   
>   static void update_config(void *handle, struct cp_psp_stream_config *config)
> @@ -555,11 +555,12 @@ struct hdcp_workqueue *hdcp_create_workqueue(struct amdgpu_device *adev, struct
>   {
>   
>   	int max_caps = dc->caps.max_links;
> -	struct hdcp_workqueue *hdcp_work = kzalloc(max_caps*sizeof(*hdcp_work), GFP_KERNEL);
> +	struct hdcp_workqueue *hdcp_work;
>   	int i = 0;
>   
> +	hdcp_work = kcalloc(max_caps, sizeof(*hdcp_work), GFP_KERNEL);
>   	if (hdcp_work == NULL)
> -		goto fail_alloc_context;
> +		return NULL;
>   
>   	hdcp_work->srm = kcalloc(PSP_HDCP_SRM_FIRST_GEN_MAX_SIZE, sizeof(*hdcp_work->srm), GFP_KERNEL);
>   
> @@ -602,9 +603,9 @@ struct hdcp_workqueue *hdcp_create_workqueue(struct amdgpu_device *adev, struct
>   	return hdcp_work;
>   
>   fail_alloc_context:
> -	kfree(hdcp_work);
>   	kfree(hdcp_work->srm);
>   	kfree(hdcp_work->srm_temp);
> +	kfree(hdcp_work);
>   
>   	return NULL;
>