#include "Python.h"

#include "pycore_fileutils.h"     // _Py_fstat_noraise()

#include "pycore_initconfig.h"

#include "pycore_pyhash.h"        // _Py_HashSecret_t

#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 __builtin_available(macOS 10.12, iOS 10.10, tvOS 10.0, watchOS 3.0, *)

#  endif

#endif

#ifndef HAVE_GETENTRYPY_GETRANDOM_RUNTIME

#  define HAVE_GETENTRYPY_GETRANDOM_RUNTIME 1

#endif

#ifdef Py_DEBUG

int _Py_HashSecret_Initialized = 0;

#else

static int _Py_HashSecret_Initialized = 0;

#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 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) 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)

{

    /* 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;

    int flags;

    char *dest;

    long n;

    if (!getrandom_works) {

        return 0;

    }

    flags = blocking ? 0 : GRND_NONBLOCK;

    dest = buffer;

    while (0 < size) {

#if defined(__sun) && defined(__SVR4)

        /* 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);

        }

#  ifdef _Py_MEMORY_SANITIZER

        if (n > 0) {

             __msan_unpoison(dest, n);

        }

#  endif

#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;

            }

            /* getrandom(GRND_NONBLOCK) fails with EAGAIN if the system urandom

               is not initialized 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;

            }

            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 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 (_PyRuntime.pyhash_state.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)

{

    int fd;

    Py_ssize_t n;

    if (raise) {

        struct _Py_stat_struct st;

        int fstat_result;

        if (urandom_cache.fd >= 0) {

            Py_BEGIN_ALLOW_THREADS

            fstat_result = _Py_fstat_noraise(urandom_cache.fd, &st);

            Py_END_ALLOW_THREADS

            /* Does the fd point to the same thing as before? (issue #21207) */

            if (fstat_result

                || 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 {

            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 {

                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;

                }

            }

        }

        do {

            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;

}

static void

dev_urandom_close(void)

{

    if (urandom_cache.fd >= 0) {

        close(urandom_cache.fd);

        urandom_cache.fd = -1;

    }

}

#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)

{

    size_t index;

    unsigned int x;

    x = x0;

    for (index=0; index < size; index++) {

        x *= 214013;

        x += 2531011;

        /* modulo 2 ^ (8 * sizeof(int)) */

        buffer[index] = (x >> 16) & 0xff;

    }

}

/* 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)

{

#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY)

    int res;

#endif

    if (size < 0) {

        if (raise) {

            PyErr_Format(PyExc_ValueError,

                         "negative argument not allowed");

        }

        return -1;

    }

    if (size == 0) {

        return 0;

    }

#ifdef MS_WINDOWS

    return win32_urandom((unsigned char *)buffer, size, raise);

#else

#if defined(PY_GETRANDOM) || defined(PY_GETENTROPY)

    if (HAVE_GETENTRYPY_GETRANDOM_RUNTIME) {

#ifdef PY_GETRANDOM

        res = py_getrandom(buffer, size, blocking, 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 or EPERM. Fall back on reading from /dev/urandom. */

        } /* end of availability block */

#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.

   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, 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);

}

PyStatus

_Py_HashRandomization_Init(const PyConfig *config)

{

    void *secret = &_Py_HashSecret;

    Py_ssize_t secret_size = sizeof(_Py_HashSecret_t);

    if (_Py_HashSecret_Initialized) {

        return _PyStatus_OK();

    }

    _Py_HashSecret_Initialized = 1;

    if (config->use_hash_seed) {

        if (config->hash_seed == 0) {

            /* disable the randomized hash */

            memset(secret, 0, secret_size);

        }

        else {

            /* use the specified hash seed */

            lcg_urandom(config->hash_seed, secret, secret_size);

        }

    }

    else {

        /* use a random hash seed */

        int res;

        /* _PyRandom_Init() is called very early in the Python initialization

           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) {

            return _PyStatus_ERR("failed to get random numbers "

                                 "to initialize Python");

        }

    }

    return _PyStatus_OK();

}

void

_Py_HashRandomization_Fini(void)

{

#ifndef MS_WINDOWS

    dev_urandom_close();

#endif

}