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util: Add general low-level random bytes helper

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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>
This commit is contained in:
David Gibson 2024-11-14 14:33:08 +11:00 • committed by Stefano Brivio
parent a60703e899
commit 71d5deed5e
3 changed files with 57 additions and 29 deletions

30
passt.c
View file

@ -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));
}
/**