Fix CVE-2016-7950:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-7950

Patch copied from upstream source repository:

https://cgit.freedesktop.org/xorg/lib/libXrender/commit/?id=8fad00b0b647ee662ce4737ca15be033b7a21714

From 8fad00b0b647ee662ce4737ca15be033b7a21714 Mon Sep 17 00:00:00 2001
From: Tobias Stoeckmann <tobias@stoeckmann.org>
Date: Sun, 25 Sep 2016 21:42:09 +0200
Subject: [PATCH] Avoid OOB write in XRenderQueryFilters

The memory for filter names is reserved right after receiving the reply.
After that, filters are iterated and each individual filter name is
stored in that reserved memory.

The individual name lengths are not checked for validity, which means
that a malicious server can reserve less memory than it will write to
during each iteration.

v2: consume remaining bytes in reply buffer on error.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>
---
 src/Filter.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/Filter.c b/src/Filter.c
index edfa572..8d701eb 100644
--- a/src/Filter.c
+++ b/src/Filter.c
@@ -38,7 +38,7 @@ XRenderQueryFilters (Display *dpy, Drawable drawable)
     char			*name;
     char			len;
     int				i;
-    unsigned long		nbytes, nbytesAlias, nbytesName;
+    unsigned long		nbytes, nbytesAlias, nbytesName, reply_left;
 
     if (!RenderHasExtension (info))
 	return NULL;
@@ -114,6 +114,7 @@ XRenderQueryFilters (Display *dpy, Drawable drawable)
      * Read the filter aliases
      */
     _XRead16Pad (dpy, filters->alias, 2 * rep.numAliases);
+    reply_left = 8 + rep.length - 2 * rep.numAliases;;
 
     /*
      * Read the filter names
@@ -122,9 +123,19 @@ XRenderQueryFilters (Display *dpy, Drawable drawable)
     {
 	int	l;
 	_XRead (dpy, &len, 1);
+	reply_left--;
 	l = len & 0xff;
+	if ((unsigned long)l + 1 > nbytesName) {
+            _XEatDataWords(dpy, reply_left);
+	    Xfree(filters);
+	    UnlockDisplay (dpy);
+	    SyncHandle ();
+	    return NULL;
+	}
+	nbytesName -= l + 1;
 	filters->filter[i] = name;
 	_XRead (dpy, name, l);
+        reply_left -= l;
 	name[l] = '\0';
 	name += l + 1;
     }
-- 
2.10.1

