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Restore getrandom(2) path for Linux with glibc 2.36 or later

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This is a follow-up to commit b120f5e38d (avoid fork-unsafe arc4random
implementations, 2018-09-04).

Avoid defining a no-op fill_random_bytes_syscall() if arc4random_buf(3)
exists, but we are unsure if it is fork-safe. Check for other options
instead. IOW, see if getrandom(2) is available.

glibc 2.36, released in 2022, started to provide arc4random_buf(3) on
Linux. This causes fill_random_bytes_syscall() to use neither of them
and makes Random.urandom solely rely on getentropy(3) via
fill_random_bytes_urandom().

While the glibc implementation is safe, I did not add it to the list
because using getrandom(2) directly is preferable on Linux.
This commit is contained in:
Kazuki Yamaguchi 2025-06-20 19:21:55 +09:00 • committed by Nobuyoshi Nakada
parent 1181a682a6
commit 0cec4a14fb
1 changed files with 5 additions and 7 deletions
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12
random.c
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@ -554,18 +554,16 @@ fill_random_bytes_syscall(void *seed, size_t size, int unused)
}
return 0;
}
#elif defined(HAVE_ARC4RANDOM_BUF)
#elif defined(HAVE_ARC4RANDOM_BUF) && \
((defined(__OpenBSD__) && OpenBSD >= 201411) || \
(defined(__NetBSD__) && __NetBSD_Version__ >= 700000000) || \
(defined(__FreeBSD__) && __FreeBSD_version >= 1200079))
// [Bug #15039] arc4random_buf(3) should used only if we know it is fork-safe
static int
fill_random_bytes_syscall(void *buf, size_t size, int unused)
{
#if (defined(__OpenBSD__) && OpenBSD >= 201411) || \
(defined(__NetBSD__) && __NetBSD_Version__ >= 700000000) || \
(defined(__FreeBSD__) && __FreeBSD_version >= 1200079)
arc4random_buf(buf, size);
return 0;
#else
return -1;
#endif
}
#elif defined(_WIN32)