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passt: Seed libc's pseudo random number generator

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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>
This commit is contained in:
David Gibson 2024-11-14 14:33:09 +11:00 committed by Stefano Brivio
parent 71d5deed5e
commit b39760cc7d
1 changed files with 10 additions and 3 deletions
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13
passt.c
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@ -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 * @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)); 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); tap_sock_init(&c);
secret_init(&c); random_init(&c);
if (clock_gettime(CLOCK_MONOTONIC, &now)) if (clock_gettime(CLOCK_MONOTONIC, &now))
die_perror("Failed to get CLOCK_MONOTONIC time"); die_perror("Failed to get CLOCK_MONOTONIC time");