If you're just following along on the mailing list, without actively
trying to apply this to a glibc tree, that diff might be hard to read.
The meat of it is the below function implementation. Notably this is
basically the same as systemd's crypto_random_bytes() (which I recently
rewrote there).
void
__arc4random_buf (void *p, size_t n)
{
static bool have_getrandom = true, seen_initialized = false;
int fd;
if (n == 0)
return;
for (;;)
{
ssize_t l;
if (!have_getrandom)
break;
l = __getrandom_nocancel (p, n, 0);
if (l > 0)
{
if ((size_t) l == n)
return; /* Done reading, success. */
p = (uint8_t *) p + l;
n -= l;
continue; /* Interrupted by a signal; keep going. */
}
else if (l == 0)
arc4random_getrandom_failure (); /* Weird, should never happen. */
else if (errno == ENOSYS)
{
have_getrandom = false;
break; /* No syscall, so fallback to /dev/urandom. */
}
arc4random_getrandom_failure (); /* Unknown other error, should never happen. */
}
if (!seen_initialized)
{
struct pollfd pfd = { .events = POLLIN };
pfd.fd = TEMP_FAILURE_RETRY (__open64_nocancel ("/dev/random", O_RDONLY | O_CLOEXEC | O_NOCTTY));
if (pfd.fd < 0)
arc4random_getrandom_failure ();
if (__poll(&pfd, 1, -1) < 0)
arc4random_getrandom_failure ();
if (__close_nocancel(pfd.fd) < 0)
arc4random_getrandom_failure ();
seen_initialized = true;
}
fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC | O_NOCTTY);
if (fd < 0)
arc4random_getrandom_failure ();
while (n)
{
ssize_t l = TEMP_FAILURE_RETRY (__read_nocancel (fd, p, n));
if (l <= 0)
arc4random_getrandom_failure ();
p = (uint8_t *) p + l;
n -= l;
}
if (__close_nocancel (fd) < 0)
arc4random_getrandom_failure ();
}
libc_hidden_def (__arc4random_buf)
weak_alias (__arc4random_buf, arc4random_buf)
