Merge pull request #377 from besser82/topic/besser82/salt_c_random

libmisc/salt.c: Obtain random bytes from /dev/urandom.

libmisc/salt.c

@@ -11,11 +11,10 @@
 
 #ident "$Id$"
 
-#include <sys/time.h>
-#include <string.h>
-#include <stdlib.h>
-#include <stdio.h>
 #include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include "prototypes.h"
 #include "defines.h"
 #include "getdef.h"
@@ -74,7 +73,7 @@
 #define GENSALT_SETTING_SIZE 100
 
 /* local function prototypes */
-static void seedRNG (void);
+static long read_random_bytes (void);
 static /*@observer@*/const char *gensalt (size_t salt_size);
 #if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
 static long shadow_random (long min, long max);
@@ -125,23 +124,27 @@ static /*@observer@*/char *l64a (long value)
 }
 #endif /* !HAVE_L64A */
 
-static void seedRNG (void)
+/* Read sizeof (long) random bytes from /dev/urandom. */
+static long read_random_bytes (void)
 {
-	struct timeval tv;
+	long randval = 0;
-	static int seeded = 0;
+	FILE *f = fopen ("/dev/urandom", "r");
 
-	if (0 == seeded) {
+	if (fread (&randval, sizeof (randval), 1, f) != sizeof (randval))
-		(void) gettimeofday (&tv, NULL);
+	{
-		srandom (tv.tv_sec ^ tv.tv_usec ^ getpid ());
+		fprintf (shadow_logfd,
-		seeded = 1;
+			 _("Unable to read from /dev/urandom.\n"));
+
+		fclose(f);
+		exit (1);
 	}
+
+	fclose(f);
+
+	return randval;
 }
 
 #if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
-/* It is not clear what is the maximum value of random().
- * We assume 2^31-1.*/
-#define RANDOM_MAX 0x7FFFFFFF
-
 /*
  * Return a random number between min and max (both included).
  *
@@ -151,8 +154,9 @@ static long shadow_random (long min, long max)
 {
 	double drand;
 	long ret;
-	seedRNG ();
+
-	drand = (double) (max - min + 1) * random () / RANDOM_MAX;
+	drand = (double) (read_random_bytes () & RAND_MAX) / (double) RAND_MAX;
+	drand *= (double) (max - min + 1);
 	/* On systems were this is not random() range is lower, we favor
 	 * higher numbers of salt. */
 	ret = (long) (max + 1 - drand);
@@ -216,7 +220,14 @@ static /*@observer@*/void SHA_salt_rounds_to_buf (char *buf, /*@null@*/int *pref
 		return;
 	}
 
-	/* Check if the result buffer is long enough. */
+	/*
+	 * Check if the result buffer is long enough.
+	 * We are going to write a maximum of 17 bytes,
+	 * plus one byte for the terminator.
+	 *    rounds=XXXXXXXXX$
+	 *    00000000011111111
+	 *    12345678901234567
+	 */
 	assert (GENSALT_SETTING_SIZE > buf_begin + 17);
 
 	(void) snprintf (buf + buf_begin, 18, "rounds=%lu$", rounds);
@@ -274,7 +285,14 @@ static /*@observer@*/void BCRYPT_salt_rounds_to_buf (char *buf, /*@null@*/int *p
 		rounds = 19;
 	}
 
-	/* Check if the result buffer is long enough. */
+	/*
+	 * Check if the result buffer is long enough.
+	 * We are going to write three bytes,
+	 * plus one byte for the terminator.
+	 *    XX$
+	 *    000
+	 *    123
+	 */
 	assert (GENSALT_SETTING_SIZE > buf_begin + 3);
 
 	(void) snprintf (buf + buf_begin, 4, "%2.2lu$", rounds);
@@ -308,8 +326,15 @@ static /*@observer@*/void YESCRYPT_salt_cost_to_buf (char *buf, /*@null@*/int *p
 		cost = Y_COST_MAX;
 	}
 
-	/* Check if the result buffer is long enough. */
+	/*
-	assert (GENSALT_SETTING_SIZE > buf_begin + 3);
+	 * Check if the result buffer is long enough.
+	 * We are going to write four bytes,
+	 * plus one byte for the terminator.
+	 *    jXX$
+	 *    0000
+	 *    1234
+	 */
+	assert (GENSALT_SETTING_SIZE > buf_begin + 4);
 
 	buf[buf_begin + 0] = 'j';
 	if (cost < 3) {
@@ -333,10 +358,9 @@ static /*@observer@*/const char *gensalt (size_t salt_size)
 
 	assert (salt_size >= MIN_SALT_SIZE &&
 	        salt_size <= MAX_SALT_SIZE);
-	seedRNG ();
+	strcat (salt, l64a (read_random_bytes ()));
-	strcat (salt, l64a (random()));
 	do {
-		strcat (salt, l64a (random()));
+		strcat (salt, l64a (read_random_bytes ()));
 	} while (strlen (salt) < salt_size);
 
 	salt[salt_size] = '\0';