faraphel/chrony
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

util: fall back to reading /dev/urandom when getrandom() blocks

Browse source 
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.
This commit is contained in:
Miroslav Lichvar 2018-05-17 14:16:58 +02:00
parent 8cbc68f28f
commit 7c5bd948bb
1 changed files with 1 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
util.c
View file

@ -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;
}