diff options
Diffstat (limited to 'Python/random.c')
| -rw-r--r-- | Python/random.c | 525 |
1 files changed, 379 insertions, 146 deletions
diff --git a/Python/random.c b/Python/random.c index af3d0bd..31f61d0 100644 --- a/Python/random.c +++ b/Python/random.c @@ -1,11 +1,23 @@ #include "Python.h" #ifdef MS_WINDOWS -#include <windows.h> +# include <windows.h> +/* All sample MSDN wincrypt programs include the header below. It is at least + * required with Min GW. */ +# include <wincrypt.h> #else -#include <fcntl.h> -#ifdef HAVE_SYS_STAT_H -#include <sys/stat.h> -#endif +# include <fcntl.h> +# ifdef HAVE_SYS_STAT_H +# include <sys/stat.h> +# endif +# ifdef HAVE_LINUX_RANDOM_H +# include <linux/random.h> +# endif +# if defined(HAVE_SYS_RANDOM_H) && (defined(HAVE_GETRANDOM) || defined(HAVE_GETENTROPY)) +# include <sys/random.h> +# endif +# if !defined(HAVE_GETRANDOM) && defined(HAVE_GETRANDOM_SYSCALL) +# include <sys/syscall.h> +# endif #endif #ifdef Py_DEBUG @@ -28,10 +40,9 @@ win32_urandom_init(int raise) return 0; error: - if (raise) + if (raise) { PyErr_SetFromWindowsErr(0); - else - Py_FatalError("Failed to initialize Windows random API (CryptoGen)"); + } return -1; } @@ -44,8 +55,9 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) if (hCryptProv == 0) { - if (win32_urandom_init(raise) == -1) + if (win32_urandom_init(raise) == -1) { return -1; + } } while (size > 0) @@ -54,11 +66,9 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) if (!CryptGenRandom(hCryptProv, (DWORD)chunk, buffer)) { /* CryptGenRandom() failed */ - if (raise) + if (raise) { PyErr_SetFromWindowsErr(0); - else - Py_FatalError("Failed to initialized the randomized hash " - "secret using CryptoGen)"); + } return -1; } buffer += chunk; @@ -67,164 +77,319 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) return 0; } -/* Issue #25003: Don' use getentropy() on Solaris (available since - * Solaris 11.3), it is blocking whereas os.urandom() should not block. */ -#elif defined(HAVE_GETENTROPY) && !defined(sun) +#else /* !MS_WINDOWS */ + +#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL) +#define PY_GETRANDOM 1 + +/* Call getrandom() to get random bytes: + + - 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). + - 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 + error. + + getrandom() is retried if it failed with EINTR: interrupted by a signal. */ +static int +py_getrandom(void *buffer, Py_ssize_t size, 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; + char *dest; + long n; + + if (!getrandom_works) { + return 0; + } + + dest = buffer; + while (0 < size) { +#ifdef sun + /* Issue #26735: On Solaris, getrandom() is limited to returning up + to 1024 bytes. Call it multiple times if more bytes are + requested. */ + n = Py_MIN(size, 1024); +#else + n = Py_MIN(size, LONG_MAX); +#endif + + errno = 0; +#ifdef HAVE_GETRANDOM + if (raise) { + Py_BEGIN_ALLOW_THREADS + n = getrandom(dest, n, flags); + Py_END_ALLOW_THREADS + } + else { + n = getrandom(dest, n, flags); + } +#else + /* On Linux, use the syscall() function because the GNU libc doesn't + expose the Linux getrandom() syscall yet. See: + https://sourceware.org/bugzilla/show_bug.cgi?id=17252 */ + if (raise) { + Py_BEGIN_ALLOW_THREADS + n = syscall(SYS_getrandom, dest, n, flags); + Py_END_ALLOW_THREADS + } + else { + n = syscall(SYS_getrandom, dest, n, flags); + } +#endif + + if (n < 0) { + /* ENOSYS: the syscall is not supported by the kernel. + EPERM: the syscall is blocked by a security policy (ex: SECCOMP) + or something else. */ + if (errno == ENOSYS || errno == EPERM) { + getrandom_works = 0; + 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; + return 0; + } + + if (errno == EINTR) { + if (raise) { + if (PyErr_CheckSignals()) { + return -1; + } + } + + /* retry getrandom() if it was interrupted by a signal */ + continue; + } + + if (raise) { + PyErr_SetFromErrno(PyExc_OSError); + } + return -1; + } + + dest += n; + size -= n; + } + return 1; +} + +#elif defined(HAVE_GETENTROPY) #define PY_GETENTROPY 1 -/* Fill buffer with size pseudo-random bytes generated by getentropy(). - Return 0 on success, or raise an exception and return -1 on error. +/* Fill buffer with size pseudo-random bytes generated by getentropy(): - If fatal is nonzero, call Py_FatalError() instead of raising an exception - on error. */ + - Return 1 on success + - Return 0 if getentropy() syscall is not available (failed with ENOSYS or + EPERM). + - Raise an exception (if raise is non-zero) and return -1 on error: + if getentropy() failed with EINTR, raise is non-zero and the Python signal + handler raised an exception, or if getentropy() failed with a different + error. + + getentropy() is retried if it failed with EINTR: interrupted by a signal. */ static int -py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal) +py_getentropy(char *buffer, Py_ssize_t size, int raise) { + /* Is getentropy() supported by the running kernel? Set to 0 if + getentropy() failed with ENOSYS or EPERM. */ + static int getentropy_works = 1; + + if (!getentropy_works) { + return 0; + } + while (size > 0) { + /* getentropy() is limited to returning up to 256 bytes. Call it + multiple times if more bytes are requested. */ Py_ssize_t len = Py_MIN(size, 256); int res; - if (!fatal) { + if (raise) { Py_BEGIN_ALLOW_THREADS res = getentropy(buffer, len); Py_END_ALLOW_THREADS - - if (res < 0) { - PyErr_SetFromErrno(PyExc_OSError); - return -1; - } } else { res = getentropy(buffer, len); - if (res < 0) - Py_FatalError("getentropy() failed"); + } + + if (res < 0) { + /* ENOSYS: the syscall is not supported by the running kernel. + EPERM: the syscall is blocked by a security policy (ex: SECCOMP) + or something else. */ + if (errno == ENOSYS || errno == EPERM) { + getentropy_works = 0; + return 0; + } + + if (errno == EINTR) { + if (raise) { + if (PyErr_CheckSignals()) { + return -1; + } + } + + /* retry getentropy() if it was interrupted by a signal */ + continue; + } + + if (raise) { + PyErr_SetFromErrno(PyExc_OSError); + } + return -1; } buffer += len; size -= len; } - return 0; + return 1; } +#endif /* defined(HAVE_GETENTROPY) && !defined(sun) */ + -#else static struct { int fd; dev_t st_dev; ino_t st_ino; } urandom_cache = { -1 }; -/* Read size bytes from /dev/urandom into buffer. - Call Py_FatalError() on error. */ -static void -dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size) -{ - int fd; - Py_ssize_t n; +/* Read random bytes from the /dev/urandom device: - assert (0 < size); + - Return 0 on success + - Raise an exception (if raise is non-zero) and return -1 on error - fd = _Py_open("/dev/urandom", O_RDONLY); - if (fd < 0) - Py_FatalError("Failed to open /dev/urandom"); + Possible causes of errors: - while (0 < size) - { - do { - n = read(fd, buffer, (size_t)size); - } while (n < 0 && errno == EINTR); - if (n <= 0) - { - /* stop on error or if read(size) returned 0 */ - Py_FatalError("Failed to read bytes from /dev/urandom"); - break; - } - buffer += n; - size -= (Py_ssize_t)n; - } - close(fd); -} + - open() failed with ENOENT, ENXIO, ENODEV, EACCES: the /dev/urandom device + was not found. For example, it was removed manually or not exposed in a + chroot or container. + - open() failed with a different error + - fstat() failed + - read() failed or returned 0 + + read() is retried if it failed with EINTR: interrupted by a signal. + + The file descriptor of the device is kept open between calls to avoid using + many file descriptors when run in parallel from multiple threads: + see the issue #18756. + + st_dev and st_ino fields of the file descriptor (from fstat()) are cached to + check if the file descriptor was replaced by a different file (which is + likely a bug in the application): see the issue #21207. -/* Read size bytes from /dev/urandom into buffer. - Return 0 on success, raise an exception and return -1 on error. */ + If the file descriptor was closed or replaced, open a new file descriptor + but don't close the old file descriptor: it probably points to something + important for some third-party code. */ static int -dev_urandom_python(char *buffer, Py_ssize_t size) +dev_urandom(char *buffer, Py_ssize_t size, int raise) { int fd; Py_ssize_t n; - struct stat st; - if (size <= 0) - return 0; + if (raise) { + struct _Py_stat_struct st; - if (urandom_cache.fd >= 0) { - /* Does the fd point to the same thing as before? (issue #21207) */ - if (fstat(urandom_cache.fd, &st) - || st.st_dev != urandom_cache.st_dev - || st.st_ino != urandom_cache.st_ino) { - /* Something changed: forget the cached fd (but don't close it, - since it probably points to something important for some - third-party code). */ - urandom_cache.fd = -1; - } - } - if (urandom_cache.fd >= 0) - fd = urandom_cache.fd; - else { - Py_BEGIN_ALLOW_THREADS - fd = _Py_open("/dev/urandom", O_RDONLY); - Py_END_ALLOW_THREADS - if (fd < 0) - { - if (errno == ENOENT || errno == ENXIO || - errno == ENODEV || errno == EACCES) - PyErr_SetString(PyExc_NotImplementedError, - "/dev/urandom (or equivalent) not found"); - else - PyErr_SetFromErrno(PyExc_OSError); - return -1; - } if (urandom_cache.fd >= 0) { - /* urandom_fd was initialized by another thread while we were - not holding the GIL, keep it. */ - close(fd); - fd = urandom_cache.fd; + /* Does the fd point to the same thing as before? (issue #21207) */ + if (_Py_fstat_noraise(urandom_cache.fd, &st) + || st.st_dev != urandom_cache.st_dev + || st.st_ino != urandom_cache.st_ino) { + /* Something changed: forget the cached fd (but don't close it, + since it probably points to something important for some + third-party code). */ + urandom_cache.fd = -1; + } } + if (urandom_cache.fd >= 0) + fd = urandom_cache.fd; else { - if (fstat(fd, &st)) { - PyErr_SetFromErrno(PyExc_OSError); - close(fd); + fd = _Py_open("/dev/urandom", O_RDONLY); + if (fd < 0) { + if (errno == ENOENT || errno == ENXIO || + errno == ENODEV || errno == EACCES) { + PyErr_SetString(PyExc_NotImplementedError, + "/dev/urandom (or equivalent) not found"); + } + /* otherwise, keep the OSError exception raised by _Py_open() */ return -1; } + if (urandom_cache.fd >= 0) { + /* urandom_fd was initialized by another thread while we were + not holding the GIL, keep it. */ + close(fd); + fd = urandom_cache.fd; + } else { - urandom_cache.fd = fd; - urandom_cache.st_dev = st.st_dev; - urandom_cache.st_ino = st.st_ino; + if (_Py_fstat(fd, &st)) { + close(fd); + return -1; + } + else { + urandom_cache.fd = fd; + urandom_cache.st_dev = st.st_dev; + urandom_cache.st_ino = st.st_ino; + } } } - } - Py_BEGIN_ALLOW_THREADS - do { do { - n = read(fd, buffer, (size_t)size); - } while (n < 0 && errno == EINTR); - if (n <= 0) - break; - buffer += n; - size -= (Py_ssize_t)n; - } while (0 < size); - Py_END_ALLOW_THREADS - - if (n <= 0) - { - /* stop on error or if read(size) returned 0 */ - if (n < 0) - PyErr_SetFromErrno(PyExc_OSError); - else - PyErr_Format(PyExc_RuntimeError, - "Failed to read %zi bytes from /dev/urandom", - size); - return -1; + n = _Py_read(fd, buffer, (size_t)size); + if (n == -1) + return -1; + if (n == 0) { + PyErr_Format(PyExc_RuntimeError, + "Failed to read %zi bytes from /dev/urandom", + size); + return -1; + } + + buffer += n; + size -= n; + } while (0 < size); + } + else { + fd = _Py_open_noraise("/dev/urandom", O_RDONLY); + if (fd < 0) { + return -1; + } + + while (0 < size) + { + do { + n = read(fd, buffer, (size_t)size); + } while (n < 0 && errno == EINTR); + + if (n <= 0) { + /* stop on error or if read(size) returned 0 */ + close(fd); + return -1; + } + + buffer += n; + size -= n; + } + close(fd); } return 0; } @@ -237,8 +402,8 @@ dev_urandom_close(void) urandom_cache.fd = -1; } } +#endif /* !MS_WINDOWS */ -#endif /* HAVE_GETENTROPY */ /* Fill buffer with pseudo-random bytes generated by a linear congruent generator (LCG): @@ -261,31 +426,100 @@ lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size) } } -/* Fill buffer with size pseudo-random bytes from the operating system random - number generator (RNG). It is suitable for most cryptographic purposes - except long living private keys for asymmetric encryption. +/* Read random bytes: - Return 0 on success, raise an exception and return -1 on error. */ -int -_PyOS_URandom(void *buffer, Py_ssize_t size) + - Return 0 on success + - Raise an exception (if raise is non-zero) and return -1 on error + + Used sources of entropy ordered by preference, preferred source first: + + - CryptGenRandom() on Windows + - getrandom() function (ex: Linux and Solaris): call py_getrandom() + - getentropy() function (ex: OpenBSD): call py_getentropy() + - /dev/urandom device + + Read from the /dev/urandom device if getrandom() or getentropy() function + 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. + + 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 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 + and has access to hardware RNG, they are used as entropy sources. + + Note: the OpenSSL RAND_pseudo_bytes() function does not automatically reseed + its RNG on fork(), two child processes (with the same pid) generate the same + random numbers: see issue #18747. Kernel RNGs don't have this issue, + they have access to good quality entropy sources. + + If raise is zero: + + - Don't raise an exception on error + - Don't call the Python signal handler (don't call PyErr_CheckSignals()) if + a function fails with EINTR: retry directly the interrupted function + - Don't release the GIL to call functions. +*/ +static int +pyurandom(void *buffer, Py_ssize_t size, int raise) { +#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY) + int res; +#endif + if (size < 0) { - PyErr_Format(PyExc_ValueError, - "negative argument not allowed"); + if (raise) { + PyErr_Format(PyExc_ValueError, + "negative argument not allowed"); + } return -1; } - if (size == 0) + + if (size == 0) { return 0; + } #ifdef MS_WINDOWS - return win32_urandom((unsigned char *)buffer, size, 1); -#elif defined(PY_GETENTROPY) - return py_getentropy(buffer, size, 0); + return win32_urandom((unsigned char *)buffer, size, raise); #else - return dev_urandom_python((char*)buffer, size); + +#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY) +#ifdef PY_GETRANDOM + res = py_getrandom(buffer, size, raise); +#else + res = py_getentropy(buffer, size, raise); +#endif + if (res < 0) { + return -1; + } + if (res == 1) { + return 0; + } + /* getrandom() or getentropy() function is not available: failed with + ENOSYS, EPERM or EAGAIN. Fall back on reading from /dev/urandom. */ +#endif + + return dev_urandom(buffer, size, raise); #endif } +/* Fill buffer with size pseudo-random bytes from the operating system random + 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. */ +int +_PyOS_URandom(void *buffer, Py_ssize_t size) +{ + return pyurandom(buffer, size, 1); +} + void _PyRandom_Init(void) { @@ -324,13 +558,14 @@ _PyRandom_Init(void) } } else { -#ifdef MS_WINDOWS - (void)win32_urandom(secret, secret_size, 0); -#elif defined(PY_GETENTROPY) - (void)py_getentropy(secret, secret_size, 1); -#else - dev_urandom_noraise(secret, secret_size); -#endif + 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); + if (res < 0) { + Py_FatalError("failed to get random numbers to initialize Python"); + } } } @@ -342,8 +577,6 @@ _PyRandom_Fini(void) CryptReleaseContext(hCryptProv, 0); hCryptProv = 0; } -#elif defined(PY_GETENTROPY) - /* nothing to clean */ #else dev_urandom_close(); #endif |