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[Bug #21448] Reorder trials in fill_random_bytes

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First try dedicated system calls, such as `getrandom` or `getentropy`,
next possible libraries, then fallback to `/dev/urandom`.
This commit is contained in:
Nobuyoshi Nakada 2025-06-22 02:00:56 +09:00
parent ec20f7feb6
commit d84a811f31
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GPG key ID: 3582D74E1FEE4465
1 changed files with 38 additions and 27 deletions
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65
random.c
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@ -447,30 +447,8 @@ random_init(int argc, VALUE *argv, VALUE obj)
# define HAVE_GETRANDOM 1
#endif
#if defined(HAVE_GETENTROPY) && !defined(HAVE_GETRANDOM)
/*
* In the case both `getentropy` and `getrandom` are defined, assume
* that the former is implemented using the latter, and use the latter
* in the `syscall` version.
* Otherwise, in the case only `getentropy`, assume it is defined as
* the replacement for security purpose of `/dev/urandom`.
*/
# define MAX_SEED_LEN_PER_READ 256
static int
fill_random_bytes_urandom(void *seed, size_t size)
{
unsigned char *p = (unsigned char *)seed;
while (size) {
size_t len = size < MAX_SEED_LEN_PER_READ ? size : MAX_SEED_LEN_PER_READ;
if (getentropy(p, len) != 0) {
return -1;
}
p += len;
size -= len;
}
return 0;
}
#elif USE_DEV_URANDOM
/* fill random bytes by reading random device directly */
#if USE_DEV_URANDOM
static int
fill_random_bytes_urandom(void *seed, size_t size)
{
@ -510,6 +488,7 @@ fill_random_bytes_urandom(void *seed, size_t size)
# define fill_random_bytes_urandom(seed, size) -1
#endif
/* fill random bytes by library */
#if 0
#elif defined MAC_OS_X_VERSION_10_7 && MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7
@ -527,7 +506,7 @@ fill_random_bytes_urandom(void *seed, size_t size)
# endif
static int
fill_random_bytes_syscall(void *seed, size_t size, int unused)
fill_random_bytes_lib(void *seed, size_t size)
{
#if USE_COMMON_RANDOM
CCRNGStatus status = CCRandomGenerateBytes(seed, size);
@ -560,7 +539,7 @@ fill_random_bytes_syscall(void *seed, size_t size, int unused)
(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)
fill_random_bytes_lib(void *buf, size_t size)
{
arc4random_buf(buf, size);
return 0;
@ -643,11 +622,17 @@ fill_random_bytes_bcrypt(void *seed, size_t size)
}
static int
fill_random_bytes_syscall(void *seed, size_t size, int unused)
fill_random_bytes_lib(void *seed, size_t size)
{
if (fill_random_bytes_bcrypt(seed, size) == 0) return 0;
return fill_random_bytes_crypt(seed, size);
}
#else
# define fill_random_bytes_lib(seed, size) -1
#endif
/* fill random bytes by dedicated syscall */
#if 0
#elif defined HAVE_GETRANDOM
static int
fill_random_bytes_syscall(void *seed, size_t size, int need_secure)
@ -671,6 +656,31 @@ fill_random_bytes_syscall(void *seed, size_t size, int need_secure)
}
return -1;
}
#elif defined(HAVE_GETENTROPY)
/*
* The Open Group Base Specifications Issue 8 - IEEE Std 1003.1-2024
* https://pubs.opengroup.org/onlinepubs/9799919799/functions/getentropy.html
*
* NOTE: `getentropy`(3) on Linux is implemented using `getrandom`(2),
* prefer the latter over this if both are defined.
*/
#ifndef GETENTROPY_MAX
# define GETENTROPY_MAX 256
#endif
static int
fill_random_bytes_syscall(void *seed, size_t size, int need_secure)
{
unsigned char *p = (unsigned char *)seed;
while (size) {
size_t len = size < GETENTROPY_MAX ? size : GETENTROPY_MAX;
if (getentropy(p, len) != 0) {
return -1;
}
p += len;
size -= len;
}
return 0;
}
#else
# define fill_random_bytes_syscall(seed, size, need_secure) -1
#endif
@ -680,6 +690,7 @@ ruby_fill_random_bytes(void *seed, size_t size, int need_secure)
{
int ret = fill_random_bytes_syscall(seed, size, need_secure);
if (ret == 0) return ret;
if (fill_random_bytes_lib(seed, size) == 0) return 0;
return fill_random_bytes_urandom(seed, size);
}