[Mesa-dev] [PATCH 1/3] egl/x11_dri3: disable WL_bind_wayland_display for devices without render nodes

[Frank Binns]

Up until now, DRI3 was only used for devices that have render nodes, unless
overridden via an environment variable, with it falling back to DRI2 otherwise.
This limitation was there in order to support WL_bind_wayland_display as it
requires client opened device node fds to be authenticated, which isn't possible
when using DRI3. This is an unfortunate compromise as DRI3 provides security
benefits over DRI2.

Instead, allow DRI3 to be used for devices without render nodes but don't
advertise WL_bind_wayland_display in this case. Applications that need this
extension can still be run by disabling DRI3 support via the LIBGL_DRI3_DISABLE
environment variable.

Signed-off-by: Frank Binns <frank.binns at imgtec.com>
---
 src/egl/drivers/dri2/platform_x11.c      |  3 ++-
 src/egl/drivers/dri2/platform_x11_dri3.c | 33 +++++---------------------------
 2 files changed, 7 insertions(+), 29 deletions(-)

diff --git a/src/egl/drivers/dri2/platform_x11.c b/src/egl/drivers/dri2/platform_x11.c
index c0a4005..1b50889 100644
--- a/src/egl/drivers/dri2/platform_x11.c
+++ b/src/egl/drivers/dri2/platform_x11.c
@@ -1335,7 +1335,8 @@ dri2_initialize_x11_dri3(_EGLDriver *drv, _EGLDisplay *disp)
    disp->Extensions.EXT_buffer_age = EGL_TRUE;
 
 #ifdef HAVE_WAYLAND_PLATFORM
-   disp->Extensions.WL_bind_wayland_display = EGL_TRUE;
+   if (dri2_dpy->device_name)
+      disp->Extensions.WL_bind_wayland_display = EGL_TRUE;
 #endif
 
    if (dri2_dpy->conn) {
diff --git a/src/egl/drivers/dri2/platform_x11_dri3.c b/src/egl/drivers/dri2/platform_x11_dri3.c
index 9363a8a..b781987 100644
--- a/src/egl/drivers/dri2/platform_x11_dri3.c
+++ b/src/egl/drivers/dri2/platform_x11_dri3.c
@@ -437,29 +437,6 @@ struct dri2_egl_display_vtbl dri3_x11_display_vtbl = {
    .get_dri_drawable = dri3_get_dri_drawable,
 };
 
-static char *
-dri3_get_device_name(int fd)
-{
-   char *ret = NULL;
-
-   ret = drmGetRenderDeviceNameFromFd(fd);
-   if (ret)
-      return ret;
-
-   /* For dri3, render node support is required for WL_bind_wayland_display.
-    * In order not to regress on older systems without kernel or libdrm
-    * support, fall back to dri2. User can override it with environment
-    * variable if they don't need to use that extension.
-    */
-   if (getenv("EGL_FORCE_DRI3") == NULL) {
-      _eglLog(_EGL_WARNING, "Render node support not available, falling back to dri2");
-      _eglLog(_EGL_WARNING, "If you want to force dri3, set EGL_FORCE_DRI3 environment variable");
-   } else
-      ret = loader_get_device_name_for_fd(fd);
-
-   return ret;
-}
-
 EGLBoolean
 dri3_x11_connect(struct dri2_egl_display *dri2_dpy)
 {
@@ -539,11 +516,11 @@ dri3_x11_connect(struct dri2_egl_display *dri2_dpy)
       return EGL_FALSE;
    }
 
-   dri2_dpy->device_name = dri3_get_device_name(dri2_dpy->fd);
-   if (!dri2_dpy->device_name) {
-      close(dri2_dpy->fd);
-      return EGL_FALSE;
-   }
+   /* Only try to get a render device name since it's only needed for
+    * WL_bind_wayland_display and dri3 doesn't provide a mechanism for
+    * authenticating client opened device node fds. If this fails then
+    * don't advertise the extension. */
+   dri2_dpy->device_name = drmGetRenderDeviceNameFromFd(dri2_dpy->fd);
 
    return EGL_TRUE;
 }
-- 
2.7.4