gnu: expat: Fix CVE-2016-0718. Improve fix for CVE-2015-1283.

* gnu/packages/patches/expat-CVE-2015-1283-refix.patch,
gnu/packages/patches/expat-CVE-2016-0718.patch: New files.
* gnu/local.mk (dist_patch_DATA): Add them.
* gnu/packages/xml.scm (expat)[replacement]: New field.
(expat/fixed): New variable.
[source]: Use new patches.

1 files changed, 42 insertions, 0 deletions

diff --git a/gnu/packages/patches/expat-CVE-2015-1283-refix.patch b/gnu/packages/patches/expat-CVE-2015-1283-refix.patch
new file mode 100644
index 0000000000..af5e3bcc3e
--- /dev/null
+++ b/gnu/packages/patches/expat-CVE-2015-1283-refix.patch
@@ -0,0 +1,42 @@
+Update previous fix for CVE-2015-1283 to not rely on undefined behavior.
+
+Copied from Debian, as found in Debian package version 2.1.0-6+deb8u2.
+
+https://sources.debian.net/src/expat/2.1.0-6%2Bdeb8u2/debian/patches/CVE-2015-1283-refix.patch/
+
+From 29a11774d8ebbafe8418b4a5ffb4cc1160b194a1 Mon Sep 17 00:00:00 2001
+From: Pascal Cuoq <cuoq@trust-in-soft.com>
+Date: Sun, 15 May 2016 09:05:46 +0200
+Subject: [PATCH] Avoid relying on undefined behavior in CVE-2015-1283 fix.
+
+---
+ expat/lib/xmlparse.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/lib/xmlparse.c b/lib/xmlparse.c
+index 13e080d..cdb12ef 100644
+--- a/lib/xmlparse.c
++++ b/lib/xmlparse.c
+@@ -1695,7 +1695,8 @@ XML_GetBuffer(XML_Parser parser, int len
+   }
+ 
+   if (len > bufferLim - bufferEnd) {
+-    int neededSize = len + (int)(bufferEnd - bufferPtr);
++    /* Do not invoke signed arithmetic overflow: */
++    int neededSize = (int) ((unsigned)len + (unsigned)(bufferEnd - bufferPtr));
+ /* BEGIN MOZILLA CHANGE (sanity check neededSize) */
+     if (neededSize < 0) {
+       errorCode = XML_ERROR_NO_MEMORY;
+@@ -1729,7 +1730,8 @@ XML_GetBuffer(XML_Parser parser, int len
+       if (bufferSize == 0)
+         bufferSize = INIT_BUFFER_SIZE;
+       do {
+-        bufferSize *= 2;
++        /* Do not invoke signed arithmetic overflow: */
++        bufferSize = (int) (2U * (unsigned) bufferSize);
+ /* BEGIN MOZILLA CHANGE (prevent infinite loop on overflow) */
+       } while (bufferSize < neededSize && bufferSize > 0);
+ /* END MOZILLA CHANGE */
+-- 
+2.8.2
+