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| author | Alexander Motin <mav@FreeBSD.org> | 2021-07-21 15:25:46 +0000 |
|---|---|---|
| committer | Alexander Motin <mav@FreeBSD.org> | 2021-08-19 01:11:51 +0000 |
| commit | 09d4fe40e039d4b08a034454c36aed86571725b0 (patch) | |
| tree | 481a2b3ec2a4712a02f28f9953a68f6364a24947 /lib/libc | |
| parent | 60833696c2e90ab929ac12e9da2ac2b381f02563 (diff) | |
| download | src-09d4fe40e039d4b08a034454c36aed86571725b0.tar.gz src-09d4fe40e039d4b08a034454c36aed86571725b0.zip | |
Fix race between first rand(3) calls with _once().
Before this patch there was a chance for thread that called rand(3)
slightly later to see rand3_state already allocated, but not yet
initialized. While this API is not expected to be thread-safe, it
is not expected to crash. ztest on 64-thread system reproduced it
reliably for me.
Submitted by: avg@
MFC after: 1 month
(cherry picked from commit 3a57f08b5042f15bb8ffb2fcce99d082d225d4cf)
Diffstat (limited to 'lib/libc')
| -rw-r--r-- | lib/libc/stdlib/rand.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c index bddb0f040302..e448d1b1fd14 100644 --- a/lib/libc/stdlib/rand.c +++ b/lib/libc/stdlib/rand.c @@ -41,11 +41,13 @@ __FBSDID("$FreeBSD$"); #include <sys/param.h> #include <sys/sysctl.h> #include <assert.h> +#include <pthread.h> #include <stdbool.h> #include <stdlib.h> #include <syslog.h> #include "un-namespace.h" +#include "libc_private.h" #include "random.h" /* @@ -64,6 +66,7 @@ __FBSDID("$FreeBSD$"); * the advantage of being the one already in the tree. */ static struct __random_state *rand3_state; +static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT; static void initialize_rand3(void) @@ -78,16 +81,14 @@ initialize_rand3(void) int rand(void) { - if (rand3_state == NULL) - initialize_rand3(); + _once(&rand3_state_once, initialize_rand3); return ((int)random_r(rand3_state)); } void srand(unsigned seed) { - if (rand3_state == NULL) - initialize_rand3(); + _once(&rand3_state_once, initialize_rand3); srandom_r(rand3_state, seed); } |