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Use getrandom() if available in json_c_get_random_seed

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Lower overhead than opening & reading from /dev/urandom, and works
in chroots and other situtations where /dev/urandom is not available.
Falls back to existing methods when kernel doesn't support the syscall.
This commit is contained in:
Alan Coopersmith
2020-07-30 16:13:04 -07:00
parent 002411293d
commit 6cf4847796
3 changed files with 51 additions and 0 deletions
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41
random_seed.c
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@@ -155,6 +155,40 @@ retry:
#endif /* defined ENABLE_RDRAND */
#ifdef HAVE_GETRANDOM
#include <stdlib.h>
#ifdef HAVE_SYS_RANDOM_H
#include <sys/random.h>
#endif
static int get_getrandom_seed(void)
{
DEBUG_SEED("get_dev_random_seed");
int r;
ssize_t ret;
do {
ret = getrandom(&r, sizeof(r), 0);
} while ((ret == -1) && (errno == EINTR));
if (ret == -1)
{
if (errno == ENOSYS) /* syscall not available in kernel */
return -1;
fprintf(stderr, "error from getrandom(): %s", strerror(errno));
exit(1);
}
if (ret != sizeof(r))
return -1;
return r;
}
#endif /* defined HAVE_GETRANDOM */
/* has_dev_urandom */
#if defined(__APPLE__) || defined(__unix__) || defined(__linux__)
@@ -283,6 +317,13 @@ int json_c_get_random_seed(void)
if (has_rdrand())
return get_rdrand_seed();
#endif
#ifdef HAVE_GETRANDOM
{
int seed = get_getrandom_seed();
if (seed != -1)
return seed;
}
#endif
#if defined HAVE_DEV_RANDOM && HAVE_DEV_RANDOM
if (has_dev_urandom())
return get_dev_random_seed();