drm: Fix uabi regression by allowing garbage mode->type from userspace

Apparently xf86-video-vmware leaves the mode->type uninitialized
when feeding the mode to the kernel. Thus we have no choice but
to accept the garbage in. We'll just ignore any of the bits we
don't want. The mode type is just a hint anyway, and more
useful for the kernel->userspace direction.

Reported-by: Thomas Hellstrom <thomas@shipmail.org>
CC: Thomas Hellstrom <thomas@shipmail.org>
Cc: Adam Jackson <ajax@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Fixes: c6ed6da ("drm/uapi: Validate the mode flags/type")
References: https://lists.freedesktop.org/archives/dri-devel/2018-March/170213.html
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321211246.10152-1-ville.syrjala@linux.intel.com
Tested-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

drivers/gpu/drm/drm_modes.c

@@ -1611,7 +1611,13 @@ int drm_mode_convert_umode(struct drm_device *dev,
 	out->vscan = in->vscan;
 	out->vrefresh = in->vrefresh;
 	out->flags = in->flags;
-	out->type = in->type;
+	/*
+	 * Old xf86-video-vmware (possibly others too) used to
+	 * leave 'type' unititialized. Just ignore any bits we
+	 * don't like. It's a just hint after all, and more
+	 * useful for the kernel->userspace direction anyway.
+	 */
+	out->type = in->type & DRM_MODE_TYPE_ALL;
 	strncpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
 	out->name[DRM_DISPLAY_MODE_LEN-1] = 0;