Avoid buffer underflow on empty strings.

If an empty string is received from an x-server, do not underrun the
buffer by accessing "rep.nameLen - 1" unconditionally, which could end
up being -1.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/XvMC.c b/src/XvMC.c
index 7336760..3ee4212 100644
--- a/src/XvMC.c
+++ b/src/XvMC.c
@@ -576,9 +576,9 @@ Status XvMCGetDRInfo(Display *dpy, XvPortID port,
 	if (*name && *busID && tmpBuf) {
 	    _XRead(dpy, tmpBuf, realSize);
 	    strncpy(*name,tmpBuf,rep.nameLen);
-	    (*name)[rep.nameLen - 1] = '\0';
+	    (*name)[rep.nameLen == 0 ? 0 : rep.nameLen - 1] = '\0';
 	    strncpy(*busID,tmpBuf+rep.nameLen,rep.busIDLen);
-	    (*busID)[rep.busIDLen - 1] = '\0';
+	    (*busID)[rep.busIDLen == 0 ? 0 : rep.busIDLen - 1] = '\0';
 	    XFree(tmpBuf);
 	} else {
 	    XFree(*name);