From 7c5bd948bb7e21fa0ee22f29e97748b2d0360319 Mon Sep 17 00:00:00 2001 From: Miroslav Lichvar Date: Thu, 17 May 2018 14:16:58 +0200 Subject: [PATCH] util: fall back to reading /dev/urandom when getrandom() blocks With recent changes in the Linux kernel, the getrandom() system call may block for a long time after boot on machines that don't have enough entropy. It blocks the chronyd's initialization before it can detach from the terminal and may cause a chronyd service to fail to start due to a timeout. At least for now, enable the GRND_NONBLOCK flag to make the system call non-blocking and let the code fall back to reading /dev/urandom (which never blocks) if the system call failed with EAGAIN or any other error. This makes the start of chronyd non-deterministic with respect to files that it needs to open and possibly also makes it slightly easier to guess the transmit/receive timestamp in client requests until the urandom source is fully initialized. Signed-off-by: Peter Korsgaard --- util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/util.c b/util.c index 4b3e455..76417d5 100644 --- a/util.c +++ b/util.c @@ -1224,7 +1224,7 @@ get_random_bytes_getrandom(char *buf, unsigned int len) if (disabled) break; - if (getrandom(rand_buf, sizeof (rand_buf), 0) != sizeof (rand_buf)) { + if (getrandom(rand_buf, sizeof (rand_buf), GRND_NONBLOCK) != sizeof (rand_buf)) { disabled = 1; break; } -- 2.11.0