From 861f274862105cd30d4442fb63e24af0d2e57e66 Mon Sep 17 00:00:00 2001 From: Christopher James Halse Rogers Date: Mon, 7 Aug 2017 16:07:54 +1000 Subject: [PATCH] lib/randutils.c: Fall back gracefully when kernel doesn't support getrandom(2). MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The 3.16 kernel is supported until 2020, and various distros have kernels of the same vintage. It's entirely possible for code built against newer headers to be run against these kernels, so fall-back to the old “read /dev/{u,}random” method if the kernel doesn' support getrandom() --- lib/randutils.c | 44 ++++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 18 deletions(-) diff --git a/lib/randutils.c b/lib/randutils.c index 09dd261860..ceeb474eff 100644 --- a/lib/randutils.c +++ b/lib/randutils.c @@ -99,32 +99,40 @@ void random_get_bytes(void *buf, size_t nbytes) unsigned char *cp = (unsigned char *)buf; #ifdef HAVE_GETRANDOM + errno = 0; while (getrandom(buf, nbytes, 0) < 0) { if (errno == EINTR) continue; break; } -#else - size_t n = nbytes; - int fd = random_get_fd(); - int lose_counter = 0; - - if (fd >= 0) { - while (n > 0) { - ssize_t x = read(fd, cp, n); - if (x <= 0) { - if (lose_counter++ > 16) - break; - continue; + 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 + { + size_t n = nbytes; + int fd = random_get_fd(); + int lose_counter = 0; + + if (fd >= 0) { + while (n > 0) { + ssize_t x = read(fd, cp, n); + if (x <= 0) { + if (lose_counter++ > 16) + break; + continue; + } + n -= x; + cp += x; + lose_counter = 0; } - n -= x; - cp += x; - lose_counter = 0; - } - close(fd); + close(fd); + } } -#endif /* * We do this all the time, but this is the only source of * randomness if /dev/random/urandom is out to lunch. -- 2.47.2