Fix create_shader buf boundary check

Adding check for the length of the buf to avoid buffer overflow attack.

Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_decode.c

@@ -73,7 +73,7 @@ static int vrend_decode_create_shader(struct vrend_decode_ctx *ctx,
    uint8_t *shd_text;
    uint32_t type;
 
-   if (length < 5)
+   if (length < VIRGL_OBJ_SHADER_HDR_SIZE(0))
       return EINVAL;
 
    type = get_buf_entry(ctx, VIRGL_OBJ_SHADER_TYPE);
@@ -81,6 +81,8 @@ static int vrend_decode_create_shader(struct vrend_decode_ctx *ctx,
    offlen = get_buf_entry(ctx, VIRGL_OBJ_SHADER_OFFSET);
    num_so_outputs = get_buf_entry(ctx, VIRGL_OBJ_SHADER_SO_NUM_OUTPUTS);
 
+   if (length < VIRGL_OBJ_SHADER_HDR_SIZE(num_so_outputs))
+      return EINVAL;
    if (num_so_outputs > PIPE_MAX_SO_OUTPUTS)
       return EINVAL;