diff options
Diffstat (limited to 'Python/random.c')
| -rw-r--r-- | Python/random.c | 77 |
1 files changed, 46 insertions, 31 deletions
diff --git a/Python/random.c b/Python/random.c index 6fdce64..ea506ee 100644 --- a/Python/random.c +++ b/Python/random.c @@ -77,7 +77,7 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) } /* Issue #25003: Don't use getentropy() on Solaris (available since - Solaris 11.3), it is blocking whereas os.urandom() should not block. */ + * Solaris 11.3), it is blocking whereas os.urandom() should not block. */ #elif defined(HAVE_GETENTROPY) && !defined(sun) #define PY_GETENTROPY 1 @@ -121,24 +121,20 @@ py_getentropy(char *buffer, Py_ssize_t size, int raise) /* Call getrandom() - Return 1 on success - - Return 0 if getrandom() syscall is not available (fails with ENOSYS). + - Return 0 if getrandom() syscall is not available (fails with ENOSYS) + or if getrandom(GRND_NONBLOCK) fails with EAGAIN (blocking=0 and system + urandom not initialized yet) and raise=0. - Raise an exception (if raise is non-zero) and return -1 on error: getrandom() failed with EINTR and the Python signal handler raised an exception, or getrandom() failed with a different error. */ 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? - Need Linux kernel 3.17 or newer, or Solaris 11.3 or newer */ + /* Is getrandom() supported by the running kernel? Set to 0 if getrandom() + fails with ENOSYS. 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; @@ -146,6 +142,7 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise) return 0; } + flags = blocking ? 0 : GRND_NONBLOCK; dest = buffer; while (0 < size) { #ifdef sun @@ -185,15 +182,12 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise) getrandom_works = 0; return 0; } - if (errno == EAGAIN) { - /* If we failed with EAGAIN, the entropy pool was - uninitialized. In this case, we return failure to fall - back to 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 their + error and fall back on reading /dev/urandom which never blocks, + even if the system urandom is not initialized yet. */ + if (errno == EAGAIN && !raise && !blocking) { return 0; } @@ -228,13 +222,13 @@ static struct { } urandom_cache = { -1 }; -/* Read 'size' random bytes from getrandom(). Fall back on reading from +/* Read 'size' random bytes from py_getrandom(). Fall back on reading from /dev/urandom if getrandom() is not available. Return 0 on success. Raise an exception (if raise is non-zero) and return -1 on error. */ static int -dev_urandom(char *buffer, Py_ssize_t size, int raise) +dev_urandom(char *buffer, Py_ssize_t size, int blocking, int raise) { int fd; Py_ssize_t n; @@ -245,7 +239,7 @@ dev_urandom(char *buffer, Py_ssize_t size, int raise) assert(size > 0); #ifdef PY_GETRANDOM - res = py_getrandom(buffer, size, raise); + res = py_getrandom(buffer, size, blocking, raise); if (res < 0) { return -1; } @@ -381,7 +375,7 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size) syscall) - Don't release the GIL to call syscalls. */ static int -pyurandom(void *buffer, Py_ssize_t size, int raise) +pyurandom(void *buffer, Py_ssize_t size, int blocking, int raise) { if (size < 0) { if (raise) { @@ -400,7 +394,7 @@ pyurandom(void *buffer, Py_ssize_t size, int raise) #elif defined(PY_GETENTROPY) return py_getentropy(buffer, size, raise); #else - return dev_urandom(buffer, size, raise); + return dev_urandom(buffer, size, blocking, raise); #endif } @@ -408,11 +402,29 @@ 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. - Return 0 on success, raise an exception and return -1 on error. */ + 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 @@ -456,8 +468,11 @@ _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"); } |