diff options
Diffstat (limited to 'Python/random.c')
| -rw-r--r-- | Python/random.c | 70 |
1 files changed, 43 insertions, 27 deletions
diff --git a/Python/random.c b/Python/random.c index 31f61d03b5..c97d5e7100 100644 --- a/Python/random.c +++ b/Python/random.c @@ -87,7 +87,7 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) - Return 1 on success - Return 0 if getrandom() is not available (failed with ENOSYS or EPERM), or if getrandom(GRND_NONBLOCK) failed with EAGAIN (system urandom not - initialized yet). + initialized yet) and raise=0. - Raise an exception (if raise is non-zero) and return -1 on error: if getrandom() failed with EINTR, raise is non-zero and the Python signal handler raised an exception, or if getrandom() failed with a different @@ -95,19 +95,13 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) getrandom() is retried if it failed with EINTR: interrupted by a signal. */ static int -py_getrandom(void *buffer, Py_ssize_t size, int raise) +py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise) { /* Is getrandom() supported by the running kernel? Set to 0 if getrandom() failed with ENOSYS or EPERM. Need Linux kernel 3.17 or newer, or Solaris 11.3 or newer */ static int getrandom_works = 1; - - /* getrandom() on Linux will block if called before the kernel has - * initialized the urandom entropy pool. This will cause Python - * to hang on startup if called very early in the boot process - - * see https://bugs.python.org/issue26839. To avoid this, use the - * GRND_NONBLOCK flag. */ - const int flags = GRND_NONBLOCK; + int flags; char *dest; long n; @@ -115,6 +109,7 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise) return 0; } + flags = blocking ? 0 : GRND_NONBLOCK; dest = buffer; while (0 < size) { #ifdef sun @@ -159,15 +154,12 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise) return 0; } - if (errno == EAGAIN) { - /* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system - urandom is not initialiazed yet. In this case, fall back on - reading from /dev/urandom. - - Note: In this case the data read will not be random so - should not be used for cryptographic purposes. Retaining - the existing semantics for practical purposes. */ - getrandom_works = 0; + /* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system urandom + is not initialiazed yet. For _PyRandom_Init(), we ignore the + error and fall back on reading /dev/urandom which never blocks, + even if the system urandom is not initialized yet: + see the PEP 524. */ + if (errno == EAGAIN && !raise && !blocking) { return 0; } @@ -442,13 +434,16 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size) is not available or does not work. Prefer getrandom() over getentropy() because getrandom() supports blocking - and non-blocking mode and Python requires non-blocking RNG at startup to - initialize its hash secret: see the PEP 524. + and non-blocking mode: see the PEP 524. Python requires non-blocking RNG at + startup to initialize its hash secret, but os.urandom() must block until the + system urandom is initialized (at least on Linux 3.17 and newer). Prefer getrandom() and getentropy() over reading directly /dev/urandom because these functions don't need file descriptors and so avoid ENFILE or EMFILE errors (too many open files): see the issue #18756. + Only the getrandom() function supports non-blocking mode. + Only use RNG running in the kernel. They are more secure because it is harder to get the internal state of a RNG running in the kernel land than a RNG running in the user land. The kernel has a direct access to the hardware @@ -467,7 +462,7 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size) - Don't release the GIL to call functions. */ static int -pyurandom(void *buffer, Py_ssize_t size, int raise) +pyurandom(void *buffer, Py_ssize_t size, int blocking, int raise) { #if defined(PY_GETRANDOM) || defined(PY_GETENTROPY) int res; @@ -491,7 +486,7 @@ pyurandom(void *buffer, Py_ssize_t size, int raise) #if defined(PY_GETRANDOM) || defined(PY_GETENTROPY) #ifdef PY_GETRANDOM - res = py_getrandom(buffer, size, raise); + res = py_getrandom(buffer, size, blocking, raise); #else res = py_getentropy(buffer, size, raise); #endif @@ -502,7 +497,7 @@ pyurandom(void *buffer, Py_ssize_t size, int raise) return 0; } /* getrandom() or getentropy() function is not available: failed with - ENOSYS, EPERM or EAGAIN. Fall back on reading from /dev/urandom. */ + ENOSYS or EPERM. Fall back on reading from /dev/urandom. */ #endif return dev_urandom(buffer, size, raise); @@ -513,11 +508,29 @@ pyurandom(void *buffer, Py_ssize_t size, int raise) number generator (RNG). It is suitable for most cryptographic purposes except long living private keys for asymmetric encryption. + On Linux 3.17 and newer, the getrandom() syscall is used in blocking mode: + block until the system urandom entropy pool is initialized (128 bits are + collected by the kernel). + Return 0 on success. Raise an exception and return -1 on error. */ int _PyOS_URandom(void *buffer, Py_ssize_t size) { - return pyurandom(buffer, size, 1); + return pyurandom(buffer, size, 1, 1); +} + +/* Fill buffer with size pseudo-random bytes from the operating system random + number generator (RNG). It is not suitable for cryptographic purpose. + + On Linux 3.17 and newer (when getrandom() syscall is used), if the system + urandom is not initialized yet, the function returns "weak" entropy read + from /dev/urandom. + + Return 0 on success. Raise an exception and return -1 on error. */ +int +_PyOS_URandomNonblock(void *buffer, Py_ssize_t size) +{ + return pyurandom(buffer, size, 0, 1); } void @@ -526,7 +539,7 @@ _PyRandom_Init(void) char *env; unsigned char *secret = (unsigned char *)&_Py_HashSecret.uc; Py_ssize_t secret_size = sizeof(_Py_HashSecret_t); - assert(secret_size == sizeof(_Py_HashSecret.uc)); + Py_BUILD_ASSERT(sizeof(_Py_HashSecret_t) == sizeof(_Py_HashSecret.uc)); if (_Py_HashSecret_Initialized) return; @@ -561,8 +574,11 @@ _PyRandom_Init(void) int res; /* _PyRandom_Init() is called very early in the Python initialization - and so exceptions cannot be used (use raise=0). */ - res = pyurandom(secret, secret_size, 0); + and so exceptions cannot be used (use raise=0). + + _PyRandom_Init() must not block Python initialization: call + pyurandom() is non-blocking mode (blocking=0): see the PEP 524. */ + res = pyurandom(secret, secret_size, 0, 0); if (res < 0) { Py_FatalError("failed to get random numbers to initialize Python"); } |