meta-stx/recipes-devtools/json-c/files/json-c-CVE-2013-6371.patch

https://github.com/json-c/json-c/commit/64e36901a0614bf64a19bc3396469c66dcd0b015

* CVE-2013-6371: hash collision denial of service
* CVE-2013-6370: buffer overflow if size_t is larger than int

diff --git a/Makefile.am b/Makefile.am
index 24b9bdf..26ced27 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -23,7 +23,8 @@ libjson_cinclude_HEADERS = \
 	json_tokener.h \
 	json_util.h \
 	linkhash.h \
-	printbuf.h
+	printbuf.h \
+	random_seed.h
 
 #libjsonx_includedir = $(libdir)/json-c-@VERSION@
 #
@@ -41,7 +42,8 @@ libjson_c_la_SOURCES = \
 	json_tokener.c \
 	json_util.c \
 	linkhash.c \
-	printbuf.c
+	printbuf.c \
+	random_seed.c
 
 
 distclean-local:
diff --git a/Makefile.am.inc b/Makefile.am.inc
index fd68a25..fec591b 100644
--- a/Makefile.am.inc
+++ b/Makefile.am.inc
@@ -1,2 +1,2 @@
-AM_CFLAGS = -Wall -Werror -Wextra -Wwrite-strings -Wno-unused-parameter -std=gnu99 -D_GNU_SOURCE -D_REENTRANT
+AM_CFLAGS = -Wall -Werror -Wno-error=deprecated-declarations -Wextra -Wwrite-strings -Wno-unused-parameter -std=gnu99 -D_GNU_SOURCE -D_REENTRANT
 
diff --git a/json_object.h b/json_object.h
index 1005734..200ac40 100644
--- a/json_object.h
+++ b/json_object.h
@@ -13,6 +13,14 @@
 #ifndef _json_object_h_
 #define _json_object_h_
 
+#ifdef __GNUC__
+#define THIS_FUNCTION_IS_DEPRECATED(func) func __attribute__ ((deprecated))
+#elif defined(_MSC_VER)
+#define THIS_FUNCTION_IS_DEPRECATED(func) __declspec(deprecated) func
+#else
+#define THIS_FUNCTION_IS_DEPRECATED(func) func
+#endif
+
 #include "json_inttypes.h"
 
 #ifdef __cplusplus
@@ -279,8 +287,8 @@ extern void json_object_object_add(struct json_object* obj, const char *key,
  * @returns the json_object associated with the given field name
  * @deprecated Please use json_object_object_get_ex
  */
-extern struct json_object* json_object_object_get(struct json_object* obj,
-						  const char *key);
+THIS_FUNCTION_IS_DEPRECATED(extern struct json_object* json_object_object_get(struct json_object* obj,
+						  const char *key));
 
 /** Get the json_object associated with a given object field.  
  *
diff --git a/json_tokener.c b/json_tokener.c
index a1019c0..19de8ef 100644
--- a/json_tokener.c
+++ b/json_tokener.c
@@ -81,6 +81,7 @@ static const char* json_tokener_errors[] = {
   "object value separator ',' expected",
   "invalid string sequence",
   "expected comment",
+  "buffer size overflow"
 };
 
 const char *json_tokener_error_desc(enum json_tokener_error jerr)
@@ -243,6 +244,16 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
   tok->char_offset = 0;
   tok->err = json_tokener_success;
 
+  /* this interface is presently not 64-bit clean due to the int len argument
+     and the internal printbuf interface that takes 32-bit int len arguments
+     so the function limits the maximum string size to INT32_MAX (2GB).
+     If the function is called with len == -1 then strlen is called to check
+     the string length is less than INT32_MAX (2GB) */
+  if ((len < -1) || (len == -1 && strlen(str) > INT32_MAX)) {
+    tok->err = json_tokener_error_size;
+    return NULL;
+  }
+
   while (PEEK_CHAR(c, tok)) {
 
   redo_char:
diff --git a/json_tokener.h b/json_tokener.h
index 5471d97..a72d2bd 100644
--- a/json_tokener.h
+++ b/json_tokener.h
@@ -33,7 +33,8 @@ enum json_tokener_error {
   json_tokener_error_parse_object_key_sep,
   json_tokener_error_parse_object_value_sep,
   json_tokener_error_parse_string,
-  json_tokener_error_parse_comment
+  json_tokener_error_parse_comment,
+  json_tokener_error_size
 };
 
 enum json_tokener_state {
@@ -163,6 +164,11 @@ extern void json_tokener_set_flags(struct json_tokener *tok, int flags);
  * responsible for calling json_tokener_parse_ex with an appropriate str
  * parameter starting with the extra characters.
  *
+ * This interface is presently not 64-bit clean due to the int len argument
+ * so the function limits the maximum string size to INT32_MAX (2GB).
+ * If the function is called with len == -1 then strlen is called to check
+ * the string length is less than INT32_MAX (2GB)
+ *
  * Example:
  * @code
 json_object *jobj = NULL;
diff --git a/linkhash.c b/linkhash.c
index 5043148..712c387 100644
--- a/linkhash.c
+++ b/linkhash.c
@@ -17,6 +17,11 @@
 #include <stddef.h>
 #include <limits.h>
 
+#ifdef HAVE_ENDIAN_H
+# include <endian.h>    /* attempt to define endianness */
+#endif
+
+#include "random_seed.h"
 #include "linkhash.h"
 
 void lh_abort(const char *msg, ...)
@@ -39,14 +44,378 @@ int lh_ptr_equal(const void *k1, const void *k2)
 	return (k1 == k2);
 }
 
+/* 
+ * hashlittle from lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ * http://burtleburtle.net/bob/c/lookup3.c
+ * minor modifications to make functions static so no symbols are exported
+ * minor mofifications to compile with -Werror
+ */
+
+/*
+-------------------------------------------------------------------------------
+lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+
+These are functions for producing 32-bit hashes for hash table lookup.
+hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() 
+are externally useful functions.  Routines to test the hash are included 
+if SELF_TEST is defined.  You can use this free for any purpose.  It's in
+the public domain.  It has no warranty.
+
+You probably want to use hashlittle().  hashlittle() and hashbig()
+hash byte arrays.  hashlittle() is is faster than hashbig() on
+little-endian machines.  Intel and AMD are little-endian machines.
+On second thought, you probably want hashlittle2(), which is identical to
+hashlittle() except it returns two 32-bit hashes for the price of one.  
+You could implement hashbig2() if you wanted but I haven't bothered here.
+
+If you want to find a hash of, say, exactly 7 integers, do
+  a = i1;  b = i2;  c = i3;
+  mix(a,b,c);
+  a += i4; b += i5; c += i6;
+  mix(a,b,c);
+  a += i7;
+  final(a,b,c);
+then use c as the hash value.  If you have a variable length array of
+4-byte integers to hash, use hashword().  If you have a byte array (like
+a character string), use hashlittle().  If you have several byte arrays, or
+a mix of things, see the comments above hashlittle().  
+
+Why is this so big?  I read 12 bytes at a time into 3 4-byte integers, 
+then mix those integers.  This is fast (you can do a lot more thorough
+mixing with 12*3 instructions on 3 integers than you can with 3 instructions
+on 1 byte), but shoehorning those bytes into integers efficiently is messy.
+-------------------------------------------------------------------------------
+*/
+
+/*
+ * My best guess at if you are big-endian or little-endian.  This may
+ * need adjustment.
+ */
+#if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \
+     __BYTE_ORDER == __LITTLE_ENDIAN) || \
+    (defined(i386) || defined(__i386__) || defined(__i486__) || \
+     defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL))
+# define HASH_LITTLE_ENDIAN 1
+# define HASH_BIG_ENDIAN 0
+#elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \
+       __BYTE_ORDER == __BIG_ENDIAN) || \
+      (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel))
+# define HASH_LITTLE_ENDIAN 0
+# define HASH_BIG_ENDIAN 1
+#else
+# define HASH_LITTLE_ENDIAN 0
+# define HASH_BIG_ENDIAN 0
+#endif
+
+#define hashsize(n) ((uint32_t)1<<(n))
+#define hashmask(n) (hashsize(n)-1)
+#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
+
+/*
+-------------------------------------------------------------------------------
+mix -- mix 3 32-bit values reversibly.
+
+This is reversible, so any information in (a,b,c) before mix() is
+still in (a,b,c) after mix().
+
+If four pairs of (a,b,c) inputs are run through mix(), or through
+mix() in reverse, there are at least 32 bits of the output that
+are sometimes the same for one pair and different for another pair.
+This was tested for:
+* pairs that differed by one bit, by two bits, in any combination
+  of top bits of (a,b,c), or in any combination of bottom bits of
+  (a,b,c).
+* "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
+  the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
+  is commonly produced by subtraction) look like a single 1-bit
+  difference.
+* the base values were pseudorandom, all zero but one bit set, or 
+  all zero plus a counter that starts at zero.
+
+Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
+satisfy this are
+    4  6  8 16 19  4
+    9 15  3 18 27 15
+   14  9  3  7 17  3
+Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
+for "differ" defined as + with a one-bit base and a two-bit delta.  I
+used http://burtleburtle.net/bob/hash/avalanche.html to choose 
+the operations, constants, and arrangements of the variables.
+
+This does not achieve avalanche.  There are input bits of (a,b,c)
+that fail to affect some output bits of (a,b,c), especially of a.  The
+most thoroughly mixed value is c, but it doesn't really even achieve
+avalanche in c.
+
+This allows some parallelism.  Read-after-writes are good at doubling
+the number of bits affected, so the goal of mixing pulls in the opposite
+direction as the goal of parallelism.  I did what I could.  Rotates
+seem to cost as much as shifts on every machine I could lay my hands
+on, and rotates are much kinder to the top and bottom bits, so I used
+rotates.
+-------------------------------------------------------------------------------
+*/
+#define mix(a,b,c) \
+{ \
+  a -= c;  a ^= rot(c, 4);  c += b; \
+  b -= a;  b ^= rot(a, 6);  a += c; \
+  c -= b;  c ^= rot(b, 8);  b += a; \
+  a -= c;  a ^= rot(c,16);  c += b; \
+  b -= a;  b ^= rot(a,19);  a += c; \
+  c -= b;  c ^= rot(b, 4);  b += a; \
+}
+
+/*
+-------------------------------------------------------------------------------
+final -- final mixing of 3 32-bit values (a,b,c) into c
+
+Pairs of (a,b,c) values differing in only a few bits will usually
+produce values of c that look totally different.  This was tested for
+* pairs that differed by one bit, by two bits, in any combination
+  of top bits of (a,b,c), or in any combination of bottom bits of
+  (a,b,c).
+* "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
+  the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
+  is commonly produced by subtraction) look like a single 1-bit
+  difference.
+* the base values were pseudorandom, all zero but one bit set, or 
+  all zero plus a counter that starts at zero.
+
+These constants passed:
+ 14 11 25 16 4 14 24
+ 12 14 25 16 4 14 24
+and these came close:
+  4  8 15 26 3 22 24
+ 10  8 15 26 3 22 24
+ 11  8 15 26 3 22 24
+-------------------------------------------------------------------------------
+*/
+#define final(a,b,c) \
+{ \
+  c ^= b; c -= rot(b,14); \
+  a ^= c; a -= rot(c,11); \
+  b ^= a; b -= rot(a,25); \
+  c ^= b; c -= rot(b,16); \
+  a ^= c; a -= rot(c,4);  \
+  b ^= a; b -= rot(a,14); \
+  c ^= b; c -= rot(b,24); \
+}
+
+
+/*
+-------------------------------------------------------------------------------
+hashlittle() -- hash a variable-length key into a 32-bit value
+  k       : the key (the unaligned variable-length array of bytes)
+  length  : the length of the key, counting by bytes
+  initval : can be any 4-byte value
+Returns a 32-bit value.  Every bit of the key affects every bit of
+the return value.  Two keys differing by one or two bits will have
+totally different hash values.
+
+The best hash table sizes are powers of 2.  There is no need to do
+mod a prime (mod is sooo slow!).  If you need less than 32 bits,
+use a bitmask.  For example, if you need only 10 bits, do
+  h = (h & hashmask(10));
+In which case, the hash table should have hashsize(10) elements.
+
+If you are hashing n strings (uint8_t **)k, do it like this:
+  for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
+
+By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
+code any way you wish, private, educational, or commercial.  It's free.
+
+Use for hash table lookup, or anything where one collision in 2^^32 is
+acceptable.  Do NOT use for cryptographic purposes.
+-------------------------------------------------------------------------------
+*/
+
+static uint32_t hashlittle( const void *key, size_t length, uint32_t initval)
+{
+  uint32_t a,b,c;                                          /* internal state */
+  union { const void *ptr; size_t i; } u;     /* needed for Mac Powerbook G4 */
+
+  /* Set up the internal state */
+  a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
+
+  u.ptr = key;
+  if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
+    const uint32_t *k = (const uint32_t *)key;         /* read 32-bit chunks */
+
+    /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
+    while (length > 12)
+    {
+      a += k[0];
+      b += k[1];
+      c += k[2];
+      mix(a,b,c);
+      length -= 12;
+      k += 3;
+    }
+
+    /*----------------------------- handle the last (probably partial) block */
+    /* 
+     * "k[2]&0xffffff" actually reads beyond the end of the string, but
+     * then masks off the part it's not allowed to read.  Because the
+     * string is aligned, the masked-off tail is in the same word as the
+     * rest of the string.  Every machine with memory protection I've seen
+     * does it on word boundaries, so is OK with this.  But VALGRIND will
+     * still catch it and complain.  The masking trick does make the hash
+     * noticably faster for short strings (like English words).
+     */
+#ifndef VALGRIND
+
+    switch(length)
+    {
+    case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
+    case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
+    case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
+    case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
+    case 8 : b+=k[1]; a+=k[0]; break;
+    case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
+    case 6 : b+=k[1]&0xffff; a+=k[0]; break;
+    case 5 : b+=k[1]&0xff; a+=k[0]; break;
+    case 4 : a+=k[0]; break;
+    case 3 : a+=k[0]&0xffffff; break;
+    case 2 : a+=k[0]&0xffff; break;
+    case 1 : a+=k[0]&0xff; break;
+    case 0 : return c;              /* zero length strings require no mixing */
+    }
+
+#else /* make valgrind happy */
+
+    const uint8_t  *k8 = (const uint8_t *)k;
+    switch(length)
+    {
+    case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
+    case 11: c+=((uint32_t)k8[10])<<16;  /* fall through */
+    case 10: c+=((uint32_t)k8[9])<<8;    /* fall through */
+    case 9 : c+=k8[8];                   /* fall through */
+    case 8 : b+=k[1]; a+=k[0]; break;
+    case 7 : b+=((uint32_t)k8[6])<<16;   /* fall through */
+    case 6 : b+=((uint32_t)k8[5])<<8;    /* fall through */
+    case 5 : b+=k8[4];                   /* fall through */
+    case 4 : a+=k[0]; break;
+    case 3 : a+=((uint32_t)k8[2])<<16;   /* fall through */
+    case 2 : a+=((uint32_t)k8[1])<<8;    /* fall through */
+    case 1 : a+=k8[0]; break;
+    case 0 : return c;
+    }
+
+#endif /* !valgrind */
+
+  } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
+    const uint16_t *k = (const uint16_t *)key;         /* read 16-bit chunks */
+    const uint8_t  *k8;
+
+    /*--------------- all but last block: aligned reads and different mixing */
+    while (length > 12)
+    {
+      a += k[0] + (((uint32_t)k[1])<<16);
+      b += k[2] + (((uint32_t)k[3])<<16);
+      c += k[4] + (((uint32_t)k[5])<<16);
+      mix(a,b,c);
+      length -= 12;
+      k += 6;
+    }
+
+    /*----------------------------- handle the last (probably partial) block */
+    k8 = (const uint8_t *)k;
+    switch(length)
+    {
+    case 12: c+=k[4]+(((uint32_t)k[5])<<16);
+             b+=k[2]+(((uint32_t)k[3])<<16);
+             a+=k[0]+(((uint32_t)k[1])<<16);
+             break;
+    case 11: c+=((uint32_t)k8[10])<<16;     /* fall through */
+    case 10: c+=k[4];
+             b+=k[2]+(((uint32_t)k[3])<<16);
+             a+=k[0]+(((uint32_t)k[1])<<16);
+             break;
+    case 9 : c+=k8[8];                      /* fall through */
+    case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
+             a+=k[0]+(((uint32_t)k[1])<<16);
+             break;
+    case 7 : b+=((uint32_t)k8[6])<<16;      /* fall through */
+    case 6 : b+=k[2];
+             a+=k[0]+(((uint32_t)k[1])<<16);
+             break;
+    case 5 : b+=k8[4];                      /* fall through */
+    case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
+             break;
+    case 3 : a+=((uint32_t)k8[2])<<16;      /* fall through */
+    case 2 : a+=k[0];
+             break;
+    case 1 : a+=k8[0];
+             break;
+    case 0 : return c;                     /* zero length requires no mixing */
+    }
+
+  } else {                        /* need to read the key one byte at a time */
+    const uint8_t *k = (const uint8_t *)key;
+
+    /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
+    while (length > 12)
+    {
+      a += k[0];
+      a += ((uint32_t)k[1])<<8;
+      a += ((uint32_t)k[2])<<16;
+      a += ((uint32_t)k[3])<<24;
+      b += k[4];
+      b += ((uint32_t)k[5])<<8;
+      b += ((uint32_t)k[6])<<16;
+      b += ((uint32_t)k[7])<<24;
+      c += k[8];
+      c += ((uint32_t)k[9])<<8;
+      c += ((uint32_t)k[10])<<16;
+      c += ((uint32_t)k[11])<<24;
+      mix(a,b,c);
+      length -= 12;
+      k += 12;
+    }
+
+    /*-------------------------------- last block: affect all 32 bits of (c) */
+    switch(length)                   /* all the case statements fall through */
+    {
+    case 12: c+=((uint32_t)k[11])<<24;
+    case 11: c+=((uint32_t)k[10])<<16;
+    case 10: c+=((uint32_t)k[9])<<8;
+    case 9 : c+=k[8];
+    case 8 : b+=((uint32_t)k[7])<<24;
+    case 7 : b+=((uint32_t)k[6])<<16;
+    case 6 : b+=((uint32_t)k[5])<<8;
+    case 5 : b+=k[4];
+    case 4 : a+=((uint32_t)k[3])<<24;
+    case 3 : a+=((uint32_t)k[2])<<16;
+    case 2 : a+=((uint32_t)k[1])<<8;
+    case 1 : a+=k[0];
+             break;
+    case 0 : return c;
+    }
+  }
+
+  final(a,b,c);
+  return c;
+}
+
 unsigned long lh_char_hash(const void *k)
 {
-	unsigned int h = 0;
-	const char* data = (const char*)k;
- 
-	while( *data!=0 ) h = h*129 + (unsigned int)(*data++) + LH_PRIME;
+	static volatile int random_seed = -1;
+
+	if (random_seed == -1) {
+		int seed;
+		/* we can't use -1 as it is the unitialized sentinel */
+		while ((seed = json_c_get_random_seed()) == -1);
+#if defined __GNUC__
+		__sync_val_compare_and_swap(&random_seed, -1, seed);
+#elif defined _MSC_VER
+		InterlockedCompareExchange(&random_seed, seed, -1);
+#else
+#warning "racy random seed initializtion if used by multiple threads"
+		random_seed = seed; /* potentially racy */
+#endif
+	}
 
-	return h;
+	return hashlittle((const char*)k, strlen((const char*)k), random_seed); 
 }
 
 int lh_char_equal(const void *k1, const void *k2)
diff --git a/linkhash.h b/linkhash.h
index 378de0b..950d09f 100644
--- a/linkhash.h
+++ b/linkhash.h
@@ -246,7 +246,7 @@ extern struct lh_entry* lh_table_lookup_entry(struct lh_table *t, const void *k)
  * @return a pointer to the found value or NULL if it does not exist.
  * @deprecated Use lh_table_lookup_ex instead.
  */
-extern const void* lh_table_lookup(struct lh_table *t, const void *k);
+THIS_FUNCTION_IS_DEPRECATED(extern const void* lh_table_lookup(struct lh_table *t, const void *k));
 
 /**
  * Lookup a record in the table
diff --git a/random_seed.c b/random_seed.c
new file mode 100644
index 0000000..3b520d4
--- /dev/null
+++ b/random_seed.c
@@ -0,0 +1,237 @@
+/*
+ * random_seed.c
+ *
+ * Copyright (c) 2013 Metaparadigm Pte. Ltd.
+ * Michael Clark <michael@metaparadigm.com>
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See COPYING for details.
+ *
+ */
+
+#include <stdio.h>
+#include "config.h"
+
+#define DEBUG_SEED(s)
+
+
+#if defined ENABLE_RDRAND
+
+/* cpuid */
+
+#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)
+#define HAS_X86_CPUID 1
+
+static void do_cpuid(int regs[], int h)
+{
+    __asm__ __volatile__(
+#if defined __x86_64__
+                         "pushq %%rbx;\n"
+#else
+                         "pushl %%ebx;\n"
+#endif
+                         "cpuid;\n"
+#if defined __x86_64__
+                         "popq %%rbx;\n"
+#else
+                         "popl %%ebx;\n"
+#endif
+                         : "=a"(regs[0]), [ebx] "=r"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
+                         : "a"(h));
+}
+
+#elif defined _MSC_VER
+
+#define HAS_X86_CPUID 1
+#define do_cpuid __cpuid
+
+#endif
+
+/* has_rdrand */
+
+#if HAS_X86_CPUID
+
+static int has_rdrand()
+{
+    // CPUID.01H:ECX.RDRAND[bit 30] == 1
+    int regs[4];
+    do_cpuid(regs, 1);
+    return (regs[2] & (1 << 30)) != 0;
+}
+
+#endif
+
+/* get_rdrand_seed - GCC x86 and X64 */
+
+#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)
+
+#define HAVE_RDRAND 1
+
+static int get_rdrand_seed()
+{
+    DEBUG_SEED("get_rdrand_seed");
+    int _eax;
+    // rdrand eax
+    __asm__ __volatile__("1: .byte 0x0F\n"
+                         "   .byte 0xC7\n"
+                         "   .byte 0xF0\n"
+                         "   jnc 1b;\n"
+                         : "=a" (_eax));
+    return _eax;
+}
+
+#endif
+
+#if defined _MSC_VER
+
+#if _MSC_VER >= 1700
+#define HAVE_RDRAND 1
+
+/* get_rdrand_seed - Visual Studio 2012 and above */
+
+static int get_rdrand_seed()
+{
+    DEBUG_SEED("get_rdrand_seed");
+    int r;
+    while (_rdrand32_step(&r) == 0);
+    return r;
+}
+
+#elif defined _M_IX86
+#define HAVE_RDRAND 1
+
+/* get_rdrand_seed - Visual Studio 2010 and below - x86 only */
+
+static int get_rdrand_seed()
+{
+	DEBUG_SEED("get_rdrand_seed");
+	int _eax;
+retry:
+	// rdrand eax
+	__asm _emit 0x0F __asm _emit 0xC7 __asm _emit 0xF0
+	__asm jnc retry
+	__asm mov _eax, eax
+	return _eax;
+}
+
+#endif
+#endif
+
+#endif /* defined ENABLE_RDRAND */
+
+
+/* has_dev_urandom */
+
+#if defined (__APPLE__) || defined(__unix__) || defined(__linux__)
+
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+
+#define HAVE_DEV_RANDOM 1
+
+static const char *dev_random_file = "/dev/urandom";
+
+static int has_dev_urandom()
+{
+    struct stat buf;
+    if (stat(dev_random_file, &buf)) {
+        return 0;
+    }
+    return ((buf.st_mode & S_IFCHR) != 0);
+}
+
+
+/* get_dev_random_seed */
+
+static int get_dev_random_seed()
+{
+    DEBUG_SEED("get_dev_random_seed");
+    
+    int fd = open(dev_random_file, O_RDONLY);
+    if (fd < 0) {
+        fprintf(stderr, "error opening %s: %s", dev_random_file, strerror(errno));
+        exit(1);
+    }
+    
+    int r;
+    ssize_t nread = read(fd, &r, sizeof(r));
+    if (nread != sizeof(r)) {
+        fprintf(stderr, "error read %s: %s", dev_random_file, strerror(errno));
+        exit(1);
+    }
+    else if (nread != sizeof(r)) {
+        fprintf(stderr, "error short read %s", dev_random_file);
+        exit(1);
+    }
+    close(fd);
+    return r;
+}
+
+#endif
+
+
+/* get_cryptgenrandom_seed */
+
+#ifdef WIN32
+
+#define HAVE_CRYPTGENRANDOM 1
+
+#include <windows.h>
+#pragma comment(lib, "advapi32.lib")
+
+static int get_cryptgenrandom_seed()
+{
+    DEBUG_SEED("get_cryptgenrandom_seed");
+    
+    HCRYPTPROV hProvider = 0;
+    int r;
+    
+    if (!CryptAcquireContextW(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
+        fprintf(stderr, "error CryptAcquireContextW");
+        exit(1);
+    }
+    
+    if (!CryptGenRandom(hProvider, sizeof(r), (BYTE*)&r)) {
+        fprintf(stderr, "error CryptGenRandom");
+        exit(1);
+    }
+    
+    CryptReleaseContext(hProvider, 0);
+    
+    return r;
+}
+
+#endif
+
+
+/* get_time_seed */
+
+#include <time.h>
+
+static int get_time_seed()
+{
+    DEBUG_SEED("get_time_seed");
+    
+    return (int)time(NULL) * 433494437;
+}
+
+
+/* json_c_get_random_seed */
+
+int json_c_get_random_seed()
+{
+#if HAVE_RDRAND
+    if (has_rdrand()) return get_rdrand_seed();
+#endif
+#if HAVE_DEV_RANDOM
+    if (has_dev_urandom()) return get_dev_random_seed();
+#endif
+#if HAVE_CRYPTGENRANDOM
+    return get_cryptgenrandom_seed();
+#endif
+    return get_time_seed();
+}
diff --git a/random_seed.h b/random_seed.h
new file mode 100644
index 0000000..7362d67
--- /dev/null
+++ b/random_seed.h
@@ -0,0 +1,25 @@
+/*
+ * random_seed.h
+ *
+ * Copyright (c) 2013 Metaparadigm Pte. Ltd.
+ * Michael Clark <michael@metaparadigm.com>
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See COPYING for details.
+ *
+ */
+
+#ifndef seed_h
+#define seed_h
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int json_c_get_random_seed();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
-- 
1.9.1

--- a/config.h.in	2013-04-03 04:04:18.000000000 +0200
+++ b/config.h.in	2014-04-10 10:32:09.318409377 +0200
@@ -3,12 +3,18 @@
 /* Define if .gnu.warning accepts long strings. */
 #undef HAS_GNU_WARNING_LONG
 
+/* Enable RDRANR Hardware RNG Hash Seed */
+#undef ENABLE_RDRAND
+
 /* Define to 1 if you have the <dlfcn.h> header file. */
 #undef HAVE_DLFCN_H
 
 /* Define to 1 if you don't have `vprintf' but do have `_doprnt.' */
 #undef HAVE_DOPRNT
 
+/* Define to 1 if you have the <endian.h> header file. */
+#undef HAVE_ENDIAN_H
+
 /* Define to 1 if you have the <fcntl.h> header file. */
 #undef HAVE_FCNTL_H
 
--- a/configure.in	2014-04-10 10:32:56.443006786 +0200
+++ b/configure.in	2014-04-10 10:34:26.480080755 +0200
@@ -15,6 +15,20 @@
 )
 AM_CONDITIONAL(ENABLE_OLDNAME_COMPAT, [test "x${enable_oldname_compat}" != "xno"])
 
+AC_ARG_ENABLE(rdrand,
+ AS_HELP_STRING([--enable-rdrand],
+   [Enable RDRAND Hardware RNG Hash Seed generation on supported x86/x64 platforms.]),
+ [if test x$enableval = xyes; then
+  enable_rdrand=yes
+  AC_DEFINE(ENABLE_RDRAND, 1, [Enable RDRANR Hardware RNG Hash Seed])
+ fi])
+
+if test "x$enable_rdrand" = "xyes"; then
+  AC_MSG_RESULT([RDRAND Hardware RNG Hash Seed enabled on supported x86/x64 platforms])
+else
+  AC_MSG_RESULT([RDRAND Hardware RNG Hash Seed disabled. Use --enable-rdrand to enable])
+fi
+
 # Checks for programs.
 
 # Checks for libraries.
@@ -23,7 +37,7 @@
 AC_CONFIG_HEADER(config.h)
 AC_CONFIG_HEADER(json_config.h)
 AC_HEADER_STDC
-AC_CHECK_HEADERS(fcntl.h limits.h strings.h syslog.h unistd.h [sys/cdefs.h] [sys/param.h] stdarg.h locale.h)
+AC_CHECK_HEADERS(fcntl.h limits.h strings.h syslog.h unistd.h [sys/cdefs.h] [sys/param.h] stdarg.h locale.h endian.h)
 AC_CHECK_HEADER(inttypes.h,[AC_DEFINE([JSON_C_HAVE_INTTYPES_H],[1],[Public define for json_inttypes.h])])
 
 # Checks for typedefs, structures, and compiler characteristics.