util: Add general low-level random bytes helper

Currently secret_init() open codes getting good quality random bytes from
the OS, either via getrandom(2) or reading /dev/random.  We're going to
add at least one more place that needs random data in future, so make a
general helper for getting random bytes.  While we're there, fix a number
of minor bugs:
 - getrandom() can theoretically return a "short read", so handle that case
 - getrandom() as well as read can return a transient EINTR
 - We would attempt to read data from /dev/random if we failed to open it
   (open() returns -1), but not if we opened it as fd 0 (unlikely, but ok)
 - More specific error reporting

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

1 files changed, 1 insertions, 29 deletions

diff --git a/passt.c b/passt.c
index fac6101..73649de 100644
--- a/passt.c
+++ b/passt.c
@@ -36,9 +36,6 @@
 #include <sys/prctl.h>
 #include <netinet/if_ether.h>
 #include <libgen.h>
-#ifdef HAS_GETRANDOM
-#include <sys/random.h>
-#endif
 
 #include "util.h"
 #include "passt.h"
@@ -118,32 +115,7 @@ static void post_handler(struct ctx *c, const struct timespec *now)
  */
 static void secret_init(struct ctx *c)
 {
-#ifndef HAS_GETRANDOM
-	int dev_random = open("/dev/random", O_RDONLY);
-	unsigned int random_read = 0;
-
-	while (dev_random && random_read < sizeof(c->hash_secret)) {
-		int ret = read(dev_random,
-			       (uint8_t *)&c->hash_secret + random_read,
-			       sizeof(c->hash_secret) - random_read);
-
-		if (ret == -1 && errno == EINTR)
-			continue;
-
-		if (ret <= 0)
-			break;
-
-		random_read += ret;
-	}
-	if (dev_random >= 0)
-		close(dev_random);
-
-	if (random_read < sizeof(c->hash_secret))
-#else
-	if (getrandom(&c->hash_secret, sizeof(c->hash_secret),
-		      GRND_RANDOM) < 0)
-#endif /* !HAS_GETRANDOM */
-		die_perror("Failed to get random bytes for hash table and TCP");
+	raw_random(&c->hash_secret, sizeof(c->hash_secret));
 }
 
 /**