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