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Fix CVE-2012-6702 and CVE-2016-5300.
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-6702
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-5300
Patch copied from:
https://sources.debian.net/src/expat/2.1.0-6%2Bdeb8u3/debian/patches/cve-2012-6702-plus-cve-2016-5300-v1.patch/
From cb31522769d11a375078a073cba94e7176cb48a4 Mon Sep 17 00:00:00 2001
From: Sebastian Pipping <sebastian@pipping.org>
Date: Wed, 16 Mar 2016 15:30:12 +0100
Subject: [PATCH] Resolve call to srand, use more entropy (patch version 1.0)
Squashed backport against vanilla Expat 2.1.1, addressing:
* CVE-2012-6702 -- unanticipated internal calls to srand
* CVE-2016-5300 -- use of too little entropy
Since commit e3e81a6d9f0885ea02d3979151c358f314bf3d6d
(released with Expat 2.1.0) Expat called srand by itself
from inside generate_hash_secret_salt for an instance
of XML_Parser if XML_SetHashSalt was either (a) not called
for that instance or if (b) salt 0 was passed to XML_SetHashSalt
prior to parsing. That call to srand passed (rather litle)
entropy extracted from the current time as a seed for srand.
That call to srand (1) broke repeatability for code calling
srand with a non-random seed prior to parsing with Expat,
and (2) resulted in a rather small set of hashing salts in
Expat in total.
For a short- to mid-term fix, the new approach avoids calling
srand altogether, extracts more entropy out of the clock and
other sources, too.
For a long term fix, we may want to read sizeof(long) bytes
from a source like getrandom(..) on Linux, and from similar
sources on other supported architectures.
https://bugzilla.redhat.com/show_bug.cgi?id=1197087
---
CMakeLists.txt | 3 +++
lib/xmlparse.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 44 insertions(+), 7 deletions(-)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 353627e..524d514 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,6 +41,9 @@ include_directories(${CMAKE_BINARY_DIR} ${CMAKE_SOURCE_DIR}/lib)
if(MSVC)
add_definitions(-D_CRT_SECURE_NO_WARNINGS -wd4996)
endif(MSVC)
+if(WIN32)
+ add_definitions(-DCOMPILED_FROM_DSP)
+endif(WIN32)
set(expat_SRCS
lib/xmlparse.c
diff --git a/lib/xmlparse.c b/lib/xmlparse.c
index e308c79..c5f942f 100644
--- a/lib/xmlparse.c
+++ b/lib/xmlparse.c
@@ -6,7 +6,14 @@
#include <string.h> /* memset(), memcpy() */
#include <assert.h>
#include <limits.h> /* UINT_MAX */
-#include <time.h> /* time() */
+
+#ifdef COMPILED_FROM_DSP
+#define getpid GetCurrentProcessId
+#else
+#include <sys/time.h> /* gettimeofday() */
+#include <sys/types.h> /* getpid() */
+#include <unistd.h> /* getpid() */
+#endif
#define XML_BUILDING_EXPAT 1
@@ -432,7 +439,7 @@ static ELEMENT_TYPE *
getElementType(XML_Parser parser, const ENCODING *enc,
const char *ptr, const char *end);
-static unsigned long generate_hash_secret_salt(void);
+static unsigned long generate_hash_secret_salt(XML_Parser parser);
static XML_Bool startParsing(XML_Parser parser);
static XML_Parser
@@ -691,11 +698,38 @@ static const XML_Char implicitContext[] = {
};
static unsigned long
-generate_hash_secret_salt(void)
+gather_time_entropy(void)
{
- unsigned int seed = time(NULL) % UINT_MAX;
- srand(seed);
- return rand();
+#ifdef COMPILED_FROM_DSP
+ FILETIME ft;
+ GetSystemTimeAsFileTime(&ft); /* never fails */
+ return ft.dwHighDateTime ^ ft.dwLowDateTime;
+#else
+ struct timeval tv;
+ int gettimeofday_res;
+
+ gettimeofday_res = gettimeofday(&tv, NULL);
+ assert (gettimeofday_res == 0);
+
+ /* Microseconds time is <20 bits entropy */
+ return tv.tv_usec;
+#endif
+}
+
+static unsigned long
+generate_hash_secret_salt(XML_Parser parser)
+{
+ /* Process ID is 0 bits entropy if attacker has local access
+ * XML_Parser address is few bits of entropy if attacker has local access */
+ const unsigned long entropy =
+ gather_time_entropy() ^ getpid() ^ (unsigned long)parser;
+
+ /* Factors are 2^31-1 and 2^61-1 (Mersenne primes M31 and M61) */
+ if (sizeof(unsigned long) == 4) {
+ return entropy * 2147483647;
+ } else {
+ return entropy * 2305843009213693951;
+ }
}
static XML_Bool /* only valid for root parser */
@@ -703,7 +737,7 @@ startParsing(XML_Parser parser)
{
/* hash functions must be initialized before setContext() is called */
if (hash_secret_salt == 0)
- hash_secret_salt = generate_hash_secret_salt();
+ hash_secret_salt = generate_hash_secret_salt(parser);
if (ns) {
/* implicit context only set for root parser, since child
parsers (i.e. external entity parsers) will inherit it
--
2.8.2
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