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lib/randutils: improve getrandom() usage 

The getrandom() does not have to return all requested bytes (missing
entropy or when interrupted by signal). The current implementation in
util-linux stupidly asks for all random data again, rather than only
for missing bytes.

The current code also does not care if we repeat our requests for
ever; that's bad.

This patch uses the same way as we already use for reading from
/dev/urandom. It means:

 * repeat getrandom() for only missing bytes
 * limit number of unsuccessful request (16 times)
 * fallback to /dev/urandom on ENOSYS (old kernel or so...)

Addresses: https://github.com/karelzak/util-linux/issues/496
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2017-08-14 10:33:06 +02:00
parent 60eedb0a53
commit 5264aebb4f
1 changed files with 47 additions and 19 deletions
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66
lib/randutils.c
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@ -95,27 +95,39 @@ int random_get_fd(void)
*/
void random_get_bytes(void *buf, size_t nbytes)
{
size_t i;
unsigned char *cp = (unsigned char *)buf;
size_t i, n = nbytes;
int lose_counter = 0;
#ifdef HAVE_GETRANDOM
errno = 0;
while (getrandom(buf, nbytes, 0) != (ssize_t)nbytes) {
if (errno == EINTR)
while (n > 0) {
int x;
errno = 0;
x = getrandom(cp, n, 0);
if (x > 0) { /* success */
n -= x;
cp += x;
lose_counter = 0;
} else if (errno == ENOSYS) { /* kernel without getrandom() */
break;
} else {
if (lose_counter++ > 16) /* entropy problem? */
break;
continue;
break;
}
}
if (errno == ENOSYS)
/*
* We've been built against headers that support getrandom,
* but the running kernel does not.
* Fallback to reading from /dev/{u,}random as before
*/
#endif
/*
* We've been built against headers that support getrandom, but the
* running kernel does not. Fallback to reading from /dev/{u,}random
* as before
*/
{
size_t n = nbytes;
int fd = random_get_fd();
int lose_counter = 0;
if (fd >= 0) {
while (n > 0) {
@ -153,7 +165,6 @@ void random_get_bytes(void *buf, size_t nbytes)
sizeof(ul_jrand_seed)-sizeof(unsigned short));
}
#endif
return;
}
@ -181,15 +192,32 @@ const char *random_tell_source(void)
}
#ifdef TEST_PROGRAM_RANDUTILS
int main(int argc __attribute__ ((__unused__)),
char *argv[] __attribute__ ((__unused__)))
int main(int argc, char *argv[])
{
unsigned int v, i;
size_t i, n;
int64_t *vp, v;
char *buf;
size_t bufsz;
/* generate and print 10 random numbers */
for (i = 0; i < 10; i++) {
n = argc == 1 ? 16 : atoi(argv[1]);
printf("Multiple random calls:\n");
for (i = 0; i < n; i++) {
random_get_bytes(&v, sizeof(v));
printf("%d\n", v);
printf("#%02zu: %25ju\n", i, v);
}
printf("One random call:\n");
bufsz = n * sizeof(*vp);
buf = malloc(bufsz);
if (!buf)
err(EXIT_FAILURE, "failed to allocate buffer");
random_get_bytes(buf, bufsz);
for (i = 0; i < n; i++) {
vp = (int64_t *) (buf + (i * sizeof(*vp)));
printf("#%02zu: %25ju\n", i, *vp);
}
return EXIT_SUCCESS;