passt: Seed libc's pseudo random number generator

We have an upcoming case where we need pseudo-random numbers to scatter
timings, but we don't need cryptographically strong random numbers.  libc's
built in random() is fine for this purpose, but we should seed it.  Extend
secret_init() - the only current user of random numbers - to do this as
well as generating the SipHash secret.  Using /dev/random for a PRNG seed
is probably overkill, but it's simple and we only do it once, so we might
as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/passt.c b/passt.c
index 73649de..83b26c5 100644
--- a/passt.c
+++ b/passt.c
@@ -110,12 +110,19 @@ static void post_handler(struct ctx *c, const struct timespec *now)
 }
 
 /**
- * secret_init() - Create secret value for SipHash calculations
+ * random_init() - Initialise things based on random data
  * @c:		Execution context
  */
-static void secret_init(struct ctx *c)
+static void random_init(struct ctx *c)
 {
+	unsigned int seed;
+
+	/* Create secret value for SipHash calculations */
 	raw_random(&c->hash_secret, sizeof(c->hash_secret));
+
+	/* Seed pseudo-RNG for things that need non-cryptographic random */
+	raw_random(&seed, sizeof(seed));
+	srandom(seed);
 }
 
 /**
@@ -236,7 +243,7 @@ int main(int argc, char **argv)
 
 	tap_sock_init(&c);
 
-	secret_init(&c);
+	random_init(&c);
 
 	if (clock_gettime(CLOCK_MONOTONIC, &now))
 		die_perror("Failed to get CLOCK_MONOTONIC time");