common: make seeding pseudo-random number generator easy

Unify how srand() calls are done, with some care to try avoiding bad seeding with hope pseudo-random numbers are unpredictable. Acked-by: Petr Vorel <petr.vorel@gmail.com> Signed-off-by: Sami Kerola <kerolasa@iki.fi>
ralfbaechle · Sep 10, 2019 · ad0256f · ad0256f
1 parent ec821e5
commit ad0256f
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Showing 6 changed files with 47 additions and 26 deletions.
diff --git a/iputils_common.c b/iputils_common.c
@@ -4,8 +4,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 
+#if HAVE_GETRANDOM
+# include <sys/random.h>
+#endif
+
 #ifdef HAVE_ERROR_H
 # include <error.h>
 #else
@@ -79,3 +84,38 @@ long strtol_or_err(char const *const str, char const *const errmesg,
 	error(EXIT_FAILURE, errno, "%s: '%s'", errmesg, str);
 	abort();
 }
+
+static unsigned int iputil_srand_fallback(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_REALTIME, &ts);
+	return ((getpid() << 16) ^ getuid() ^ ts.tv_sec ^ ts.tv_nsec);
+}
+
+void iputils_srand(void)
+{
+	unsigned int i;
+#if HAVE_GETRANDOM
+	ssize_t ret;
+
+	while ((ret = getrandom(&i, sizeof(i), GRND_NONBLOCK)) != sizeof(i)) {
+		switch(errno) {
+		case EINTR:
+			continue;
+		default:
+			i = iputil_srand_fallback();
+			break;
+		}
+	}
+#else
+	i = iputil_srand_fallback();
+#endif
+	srand(i);
+	/* Consume up to 31 random numbers */
+	i = rand() & 0x1F;
+	while (0 < i) {
+		rand();
+		i--;
+	}
+}
diff --git a/iputils_common.h b/iputils_common.h
@@ -59,5 +59,6 @@ extern int close_stream(FILE *stream);
 extern void close_stdout(void);
 extern long strtol_or_err(char const *const str, char const *const errmesg,
 			  const long min, const long max);
+extern void iputils_srand(void);
 
 #endif /* IPUTILS_COMMON_H */
diff --git a/meson.build b/meson.build
@@ -22,6 +22,7 @@ conf.set('_GNU_SOURCE', 1, description : 'Enable GNU extensions on systems that
 # Check functions.
 foreach f : '''
 	__fpending
+	getrandom
 	nanosleep
 '''.split()
 	if cc.has_function(f, args : '-D_GNU_SOURCE')

diff --git a/ninfod/ninfod_core.c b/ninfod/ninfod_core.c
@@ -305,21 +305,7 @@ void init_core(int forced)
 	DEBUG(LOG_DEBUG, "%s()\n", __func__);
 
 	if (!initialized || forced) {
-		struct timeval tv;
-		unsigned int seed = 0;
-		pid_t pid;
-
-		if (gettimeofday(&tv, NULL) < 0) {
-			DEBUG(LOG_WARNING, "%s(): failed to gettimeofday()\n", __func__);
-		} else {
-			seed = (tv.tv_usec & 0xffffffff);
-		}
-
-		pid = getpid();
-		seed ^= (((unsigned long)pid) & 0xffffffff);
-
-		srand(seed);
-
+		iputils_srand();
 #if ENABLE_THREADS
 		if (initialized)
 			pthread_attr_destroy(&pattr);

diff --git a/ping6_common.c b/ping6_common.c
@@ -176,14 +176,7 @@ struct {
 static void niquery_init_nonce(void)
 {
 #if PING6_NONCE_MEMORY
-	struct timeval tv;
-	unsigned long seed;
-
-	seed = (unsigned long)getpid();
-	if (!gettimeofday(&tv, NULL))
-		seed ^= tv.tv_usec;
-	srand(seed);
-
+	iputils_srand();
 	ni_nonce_ptr = calloc(NI_NONCE_SIZE, MAX_DUP_CHK);
 	if (!ni_nonce_ptr)
 		error(2, errno, "calloc");

diff --git a/rdisc.c b/rdisc.c
@@ -419,7 +419,7 @@ int main(int argc, char **argv)
 
 #ifdef RDISC_SERVER
 	if (responder)
-		srandom((int)gethostid());
+		iputils_srand();
 #endif
 
 	if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) {
@@ -503,7 +503,7 @@ void timer()
 		else
 			left_until_advertise = min_adv_int +
 				((max_adv_int - min_adv_int) *
-				 (random() % 1000)/1000);
+				 (rand() % 1000)/1000);
 	} else
 #endif
 	if (solicit && left_until_solicit <= 0) {
@@ -873,7 +873,7 @@ pr_pack(char *buf, int cc, struct sockaddr_in *from)
 			/* Restart the timer when we broadcast */
 			left_until_advertise = min_adv_int +
 				((max_adv_int - min_adv_int)
-				 * (random() % 1000)/1000);
+				 * (rand() % 1000)/1000);
 		} else {
 			sin.sin_addr.s_addr = ip->saddr;
 			if (!is_directly_connected(sin.sin_addr)) {