drm/amdgpu: Check if fd really is an amdgpu fd.

Otherwise we interpret the file private data as drm & amdgpu data
while it might not be, possibly allowing one to get memory corruption.
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -411,6 +411,8 @@ struct amdgpu_fpriv {
 	struct amdgpu_ctx_mgr	ctx_mgr;
 };
 
+int amdgpu_file_to_fpriv(struct file *filp, struct amdgpu_fpriv **fpriv);
+
 int amdgpu_ib_get(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 		  unsigned size, struct amdgpu_ib *ib);
 void amdgpu_ib_free(struct amdgpu_device *adev, struct amdgpu_ib *ib,

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -1178,6 +1178,22 @@ static const struct file_operations amdgpu_driver_kms_fops = {
 #endif
 };
 
+int amdgpu_file_to_fpriv(struct file *filp, struct amdgpu_fpriv **fpriv)
+{
+        struct drm_file *file;
+
+	if (!filp)
+		return -EINVAL;
+
+	if (filp->f_op != &amdgpu_driver_kms_fops) {
+		return -EINVAL;
+	}
+
+	file = filp->private_data;
+	*fpriv = file->driver_priv;
+	return 0;
+}
+
 static bool
 amdgpu_get_crtc_scanout_position(struct drm_device *dev, unsigned int pipe,
 				 bool in_vblank_irq, int *vpos, int *hpos,

drivers/gpu/drm/amd/amdgpu/amdgpu_sched.c

@@ -54,16 +54,20 @@ static int amdgpu_sched_process_priority_override(struct amdgpu_device *adev,
 						  enum drm_sched_priority priority)
 {
 	struct file *filp = fget(fd);
-	struct drm_file *file;
 	struct amdgpu_fpriv *fpriv;
 	struct amdgpu_ctx *ctx;
 	uint32_t id;
+	int r;
 
 	if (!filp)
 		return -EINVAL;
 
-	file = filp->private_data;
-	fpriv = file->driver_priv;
+	r = amdgpu_file_to_fpriv(filp, &fpriv);
+	if (r) {
+		fput(filp);
+		return r;
+	}
+
 	idr_for_each_entry(&fpriv->ctx_mgr.ctx_handles, ctx, id)
 		amdgpu_ctx_priority_override(ctx, priority);