[Cryptography] OpenSSL and random

[Florian Weimer]

* Theodore Ts'o:

> On Thu, Dec 01, 2016 at 09:47:02PM -0600, Nico Williams wrote:
>> Python could use lame rng seeds for hash table randomization, note the
>> lameness, and reseed later when cryptographically-secure an rng is
>> needed.
>
> The application can do this already using the existing API's.
>
> int get_pseudorandom_hash(char *buf, int buflen)
> {
> 	int fd, ret;
>
> 	ret = getrandom(buf, buflen, GRND_NONBLOCK);
> 	if (!ret)
> 		return 0;
> 	if (errno != EAGAIN)
> 		return -1;
> 	fd = open("/dev/urandom", O_RDONLY);
> 	if (fd < 0)
> 		return -1;
> 	while (buflen > 0) {
> 		ret = read(fd, buf, buflen);
> 		if (ret < 0)
> 			return -1;
> 		buf += ret;
> 		buflen -= ret;
> 	}
> 	close(fd);
> 	return 0;
> }

The error checks don't look right.  The errno variable won't be set if
getrandom succeeds.  The system call returns a buffer length, not just
a 0/-1 flag indicating success/failure.