#include "Python.h" #include "pycore_fileutils.h" // _Py_fstat_noraise() #include "pycore_initconfig.h" #include "pycore_pylifecycle.h" // _PyOS_URandomNonblock() #include "pycore_runtime.h" // _PyRuntime #ifdef HAVE_UNISTD_H # include <unistd.h> // close() #endif #ifdef MS_WINDOWS # include <windows.h> # include <bcrypt.h> #else # include <fcntl.h> // O_RDONLY # ifdef HAVE_SYS_STAT_H # include <sys/stat.h> # endif # ifdef HAVE_LINUX_RANDOM_H # include <linux/random.h> // GRND_NONBLOCK # endif # if defined(HAVE_SYS_RANDOM_H) && (defined(HAVE_GETRANDOM) || defined(HAVE_GETENTROPY)) # include <sys/random.h> // getrandom() # endif # if !defined(HAVE_GETRANDOM) && defined(HAVE_GETRANDOM_SYSCALL) # include <sys/syscall.h> // SYS_getrandom # endif #endif #ifdef _Py_MEMORY_SANITIZER # include <sanitizer/msan_interface.h> #endif #if defined(__APPLE__) && defined(__has_builtin) # if __has_builtin(__builtin_available) #define HAVE_GETENTRYPY_GETRANDOM_RUNTIME … # endif #endif #ifndef HAVE_GETENTRYPY_GETRANDOM_RUNTIME #define HAVE_GETENTRYPY_GETRANDOM_RUNTIME … #endif #ifdef Py_DEBUG int _Py_HashSecret_Initialized = 0; #else static int _Py_HashSecret_Initialized = …; #endif #ifdef MS_WINDOWS /* Fill buffer with size pseudo-random bytes generated by the Windows CryptoGen API. Return 0 on success, or raise an exception and return -1 on error. */ static int win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise) { while (size > 0) { DWORD chunk = (DWORD)Py_MIN(size, PY_DWORD_MAX); NTSTATUS status = BCryptGenRandom(NULL, buffer, chunk, BCRYPT_USE_SYSTEM_PREFERRED_RNG); if (!BCRYPT_SUCCESS(status)) { /* BCryptGenRandom() failed */ if (raise) { PyErr_SetFromWindowsErr(0); } return -1; } buffer += chunk; size -= chunk; } return 0; } #else /* !MS_WINDOWS */ #if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL) #define PY_GETRANDOM … /* 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) 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 error. getrandom() is retried if it failed with EINTR: interrupted by a signal. */ static int py_getrandom(void *buffer, Py_ssize_t size, int blocking, int raise) { … } #elif defined(HAVE_GETENTROPY) #define PY_GETENTROPY … /* Fill buffer with size pseudo-random bytes generated by getentropy(): - 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. */ #if defined(__APPLE__) && _Py__has_attribute(availability) static int py_getentropy(char *buffer, Py_ssize_t size, int raise) __attribute__((availability(macos,introduced=10.12))) __attribute__((availability(ios,introduced=10.0))) __attribute__((availability(tvos,introduced=10.0))) __attribute__((availability(watchos,introduced=3.0))); #endif static int 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 (raise) { Py_BEGIN_ALLOW_THREADS res = getentropy(buffer, len); Py_END_ALLOW_THREADS } else { res = getentropy(buffer, len); } 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 1; } #endif /* defined(HAVE_GETENTROPY) && !(defined(__sun) && defined(__SVR4)) */ #define urandom_cache … /* Read random bytes from the /dev/urandom device: - Return 0 on success - Raise an exception (if raise is non-zero) and return -1 on error Possible causes of errors: - 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. 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(char *buffer, Py_ssize_t size, int raise) { … } static void dev_urandom_close(void) { … } #undef urandom_cache #endif /* !MS_WINDOWS */ /* Fill buffer with pseudo-random bytes generated by a linear congruent generator (LCG): x(n+1) = (x(n) * 214013 + 2531011) % 2^32 Use bits 23..16 of x(n) to generate a byte. */ static void lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size) { … } /* Read random bytes: - 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: - BCryptGenRandom() 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: 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 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 blocking, int raise) { … } /* 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. 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) { … } /* 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) { … } PyStatus _Py_HashRandomization_Init(const PyConfig *config) { … } void _Py_HashRandomization_Fini(void) { … }
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