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lib/randutils: don't break on EAGAIN, use usleep() 

The current code uses lose_counter to make more attempts to read
random numbers. It seems better to wait a moment between attempts to
avoid busy loop (we do the same in all-io.h).

The worst case is 1 second delay for all random_get_bytes() on systems
with uninitialized entropy pool -- for example you call sfdisk (MBR Id
or GPT UUIDs) on very first boot, etc. In this case it will use libc
rand() as a fallback solution.

Note that we do not use random numbers for security sensitive things
like keys or so. It's used for random based UUIDs etc.

Addresses: https://github.com/karelzak/util-linux/pull/603
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2018-03-20 14:17:24 +01:00
parent 6ffdfda846
commit edc1c90cb9
1 changed files with 12 additions and 5 deletions
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17
lib/randutils.c
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@ -95,6 +95,9 @@ int random_get_fd(void)
* Use /dev/urandom if possible, and if not,
* use glibc pseudo-random functions.
*/
#define UL_RAND_READ_ATTEMPTS 8
#define UL_RAND_READ_DELAY 125000 /* microseconds */
void random_get_bytes(void *buf, size_t nbytes)
{
unsigned char *cp = (unsigned char *)buf;
@ -111,11 +114,14 @@ void random_get_bytes(void *buf, size_t nbytes)
n -= x;
cp += x;
lose_counter = 0;
} else if (errno == ENOSYS) /* kernel without getrandom() */
} else if (errno == ENOSYS) { /* kernel without getrandom() */
break;
else if (errno == EAGAIN)
break;
else if (lose_counter++ > 16) /* entropy problem? */
} else if (errno == EAGAIN && lose_counter < UL_RAND_READ_ATTEMPTS) {
xusleep(UL_RAND_READ_DELAY); /* no etropy, wait and try again */
lose_counter++;
} else
break;
}
@ -134,8 +140,9 @@ void random_get_bytes(void *buf, size_t nbytes)
while (n > 0) {
ssize_t x = read(fd, cp, n);
if (x <= 0) {
if (lose_counter++ > 16)
if (lose_counter++ > UL_RAND_READ_ATTEMPTS)
break;
xusleep(UL_RAND_READ_DELAY);
continue;
}
n -= x;