[PATCH] libXvMC: avoid overflowing by making nameLen and busIDLen addition overflow

[Julien Cristau]

On Mon, May 27, 2013 at 09:45:06 +1000, Dave Airlie wrote:

> From: Dave Airlie <airlied at redhat.com>
> 
> Al Viro pointed this out on lwn, and I think this patch should fix it,
> but making sure we don't do the addition as 32-bit on 64-bit machines.
> 
How about this instead:

diff --git a/src/XvMC.c b/src/XvMC.c
index 74c8b85..a78bb0d 100644
--- a/src/XvMC.c
+++ b/src/XvMC.c
@@ -573,7 +573,8 @@ Status XvMCGetDRInfo(Display *dpy, XvPortID port,
 	unsigned long realSize = 0;
 	char *tmpBuf = NULL;
 
-	if (rep.length < (INT_MAX >> 2)) {
+	if ((rep.length < (INT_MAX >> 2)) &&
+	    (rep.nameLen + rep.busIDLen >= rep.nameLen)) {
 	    realSize = rep.length << 2;
 	    if (realSize >= (rep.nameLen + rep.busIDLen)) {
 		tmpBuf = Xmalloc(realSize);

nameLen and busIDLen are unsigned int, so it should be enough to ensure
the addition doesn't wrap around?

Cheers,
Julien