gnu: libxvmc: Fix CVE-2016-7953.

* gnu/packages/patches/libxvmc-CVE-2016-7953.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/xorg.scm (libxvmc)[replacement]: New field.
(libxvmc/fixed): New variable.

gnu/local.mk

@@ -678,6 +678,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libxrender-CVE-2016-7950.patch		\
   %D%/packages/patches/libxtst-CVE-2016-7951-CVE-2016-7952.patch	\
   %D%/packages/patches/libxv-CVE-2016-5407.patch		\
+  %D%/packages/patches/libxvmc-CVE-2016-7953.patch		\
   %D%/packages/patches/libxslt-generated-ids.patch		\
   %D%/packages/patches/lirc-localstatedir.patch			\
   %D%/packages/patches/llvm-for-extempore.patch			\

gnu/packages/patches/libxvmc-CVE-2016-7953.patch

@@ -0,0 +1,42 @@
+Fix CVE-2016-7953:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-7953
+
+Patch copied from upstream source repository:
+
+https://cgit.freedesktop.org/xorg/lib/libXvMC/commit/?id=2cd95e7da8367cccdcdd5c9b160012d1dec5cbdb
+
+From 2cd95e7da8367cccdcdd5c9b160012d1dec5cbdb Mon Sep 17 00:00:00 2001
+From: Tobias Stoeckmann <tobias@stoeckmann.org>
+Date: Sun, 25 Sep 2016 22:34:27 +0200
+Subject: [PATCH] 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>
+---
+ src/XvMC.c | 4 ++--
+ 1 file 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);
+-- 
+2.10.1
+

gnu/packages/xorg.scm

@@ -4998,6 +4998,7 @@ new API's in libXft, or the legacy API's in libX11.")
 (define-public libxvmc
   (package
     (name "libxvmc")
+    (replacement libxvmc/fixed)
     (version "1.0.9")
     (source
       (origin
@@ -5023,6 +5024,13 @@ new API's in libXft, or the legacy API's in libX11.")
     (description "Xorg XvMC library.")
     (license license:x11)))
 
+(define libxvmc/fixed
+  (package
+    (inherit libxvmc)
+    (source (origin
+              (inherit (package-source libxvmc))
+              (patches (search-patches
+                         "libxvmc-CVE-2016-7953.patch"))))))
 
 (define-public libxxf86vm
   (package