XQuartz: Validate screen in AppleDRIQueryDirectRenderingCapable requests

Return an error to the caller rather than crashing the server on
invalid screens.

Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>
(cherry picked from commit b3572c0d1ab7888ac26d6b2b8be6d1d19ed9af3f)

1 files changed, 4 insertions, 0 deletions

diff --git a/hw/xquartz/xpr/appledri.c b/hw/xquartz/xpr/appledri.c
index 9aac07240..d7e984467 100644
--- a/hw/xquartz/xpr/appledri.c
+++ b/hw/xquartz/xpr/appledri.c
@@ -123,6 +123,10 @@ ProcAppleDRIQueryDirectRenderingCapable(register ClientPtr client)
     rep.length = 0;
     rep.sequenceNumber = client->sequence;
 
+    if (stuff->screen >= screenInfo.numScreens) {
+        return BadValue;
+    }
+
     if (!DRIQueryDirectRenderingCapable(screenInfo.screens[stuff->screen],
                                         &isCapable)) {
         return BadValue;