vrend: add sanity check for vertext buffer index

The vertext_buffer_index is read from guest and then used
to index the 'vbo' array in struct 'vrend_sub_context'.
Add sanity check for this to avoid oob issue.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_decode.c

@@ -612,6 +612,10 @@ static int vrend_decode_create_ve(struct vrend_decode_ctx *ctx, uint32_t handle,
          ve[i].src_offset = get_buf_entry(ctx, VIRGL_OBJ_VERTEX_ELEMENTS_V0_SRC_OFFSET(i));
          ve[i].instance_divisor = get_buf_entry(ctx, VIRGL_OBJ_VERTEX_ELEMENTS_V0_INSTANCE_DIVISOR(i));
          ve[i].vertex_buffer_index = get_buf_entry(ctx, VIRGL_OBJ_VERTEX_ELEMENTS_V0_VERTEX_BUFFER_INDEX(i));
+
+         if (ve[i].vertex_buffer_index >= PIPE_MAX_ATTRIBS)
+            return EINVAL;
+
          ve[i].src_format = get_buf_entry(ctx, VIRGL_OBJ_VERTEX_ELEMENTS_V0_SRC_FORMAT(i));
       }
    }