Date: Tue, 20 Jul 2021 17:30:33 GMT From: Alexander Motin <mav@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 28d70deaafa6 - main - Fix race between first rand(3) calls. Message-ID: <202107201730.16KHUXPM057550@gitrepo.freebsd.org>
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The branch main has been updated by mav: URL: https://cgit.FreeBSD.org/src/commit/?id=28d70deaafa62c5d1602de5272c0aad0fcca8aff commit 28d70deaafa62c5d1602de5272c0aad0fcca8aff Author: Alexander Motin <mav@FreeBSD.org> AuthorDate: 2021-07-20 17:15:08 +0000 Commit: Alexander Motin <mav@FreeBSD.org> CommitDate: 2021-07-20 17:30:28 +0000 Fix race between first rand(3) calls. 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. MFC after: 1 month --- lib/libc/stdlib/rand.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c index bddb0f040302..353f59349e1d 100644 --- a/lib/libc/stdlib/rand.c +++ b/lib/libc/stdlib/rand.c @@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$"); #include <stdbool.h> #include <stdlib.h> #include <syslog.h> +#include <machine/atomic.h> #include "un-namespace.h" #include "random.h" @@ -68,11 +69,15 @@ static struct __random_state *rand3_state; static void initialize_rand3(void) { + struct __random_state *state; int error; - rand3_state = allocatestate(TYPE_3); - error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3); + state = allocatestate(TYPE_3); + error = initstate_r(state, 1, state->rst_randtbl, BREAK_3); assert(error == 0); + if (!atomic_cmpset_rel_ptr((volatile uintptr_t *)&rand3_state, + (uintptr_t)NULL, (uintptr_t)state)) + free(state); } int
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