1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
|
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
|
