gnu: python@3.5: Fix getentropy() calls on kernels < 3.17.

* gnu/packages/patches/python-3.5-getentropy-on-old-kernels.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/python.scm (python-3.5, python-minimal, python-minimal-wrapper,
python-wrapper)[source]: Use it.

3 files changed, 722 insertions, 0 deletions

diff --git a/gnu/local.mk b/gnu/local.mk
index 3356c9e34c..c51e04289b 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -855,6 +855,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/python-3-search-paths.patch		\
   %D%/packages/patches/python-3.4-fix-tests.patch		\
   %D%/packages/patches/python-3.5-fix-tests.patch		\
+  %D%/packages/patches/python-3.5-getentropy-on-old-kernels.patch	\
   %D%/packages/patches/python-dendropy-fix-tests.patch		\
   %D%/packages/patches/python-file-double-encoding-bug.patch	\
   %D%/packages/patches/python-fix-tests.patch			\
diff --git a/gnu/packages/patches/python-3.5-getentropy-on-old-kernels.patch b/gnu/packages/patches/python-3.5-getentropy-on-old-kernels.patch
new file mode 100644
index 0000000000..8a12b5b448
--- /dev/null
+++ b/gnu/packages/patches/python-3.5-getentropy-on-old-kernels.patch
@@ -0,0 +1,720 @@
+This patch resolves a compatibility issue when compiled against glibc 2.25
+and run runder kernels < 3.17:
+
+https://bugzilla.redhat.com/show_bug.cgi?id=1410175
+
+Upstream bug URL: https://bugs.python.org/issue29157
+
+Patch copied from upstream source repository:
+
+https://hg.python.org/cpython/rev/8125d9a8152b
+
+# HG changeset patch
+# User Victor Stinner <victor.stinner@gmail.com>
+# Date 1483957133 -3600
+# Node ID 8125d9a8152b79e712cb09c7094b9129b9bcea86
+# Parent  337461574c90281630751b6095c4e1baf380cf7d
+Issue #29157: Prefer getrandom() over getentropy()
+
+Copy and then adapt Python/random.c from default branch. Difference between 3.5
+and default branches:
+
+* Python 3.5 only uses getrandom() in non-blocking mode: flags=GRND_NONBLOCK
+* If getrandom() fails with EAGAIN: py_getrandom() immediately fails and
+  remembers that getrandom() doesn't work.
+* Python 3.5 has no _PyOS_URandomNonblock() function: _PyOS_URandom()
+  works in non-blocking mode on Python 3.5
+
+diff --git a/Python/random.c b/Python/random.c
+--- Python/random.c
++++ Python/random.c
+@@ -1,6 +1,9 @@
+ #include "Python.h"
+ #ifdef MS_WINDOWS
+ #  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
+@@ -37,10 +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;
+ }
+ 
+@@ -53,8 +55,9 @@ win32_urandom(unsigned char *buffer, Py_
+ 
+     if (hCryptProv == 0)
+     {
+-        if (win32_urandom_init(raise) == -1)
++        if (win32_urandom_init(raise) == -1) {
+             return -1;
++        }
+     }
+ 
+     while (size > 0)
+@@ -63,11 +66,9 @@ win32_urandom(unsigned char *buffer, Py_
+         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;
+@@ -76,58 +77,23 @@ win32_urandom(unsigned char *buffer, Py_
+     return 0;
+ }
+ 
+-/* Issue #25003: Don't use getentropy() on Solaris (available since
+- * Solaris 11.3), it is blocking whereas os.urandom() should not block. */
+-#elif defined(HAVE_GETENTROPY) && !defined(sun)
+-#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.
+-
+-   If fatal is nonzero, call Py_FatalError() instead of raising an exception
+-   on error. */
+-static int
+-py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
+-{
+-    while (size > 0) {
+-        Py_ssize_t len = Py_MIN(size, 256);
+-        int res;
+-
+-        if (!fatal) {
+-            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");
+-        }
+-
+-        buffer += len;
+-        size -= len;
+-    }
+-    return 0;
+-}
+-
+-#else
++#else /* !MS_WINDOWS */
+ 
+ #if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
+ #define PY_GETRANDOM 1
+ 
+-/* Call getrandom()
++/* Call getrandom() to get random bytes:
++
+    - Return 1 on success
+-   - Return 0 if getrandom() syscall is not available (failed with ENOSYS or
+-     EPERM) or if getrandom(GRND_NONBLOCK) failed with EAGAIN (system urandom
+-     not initialized yet) and raise=0.
++   - 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:
+-     getrandom() failed with EINTR and the Python signal handler raised an
+-     exception, or getrandom() failed with a different 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)
+ {
+@@ -142,16 +108,19 @@ py_getrandom(void *buffer, Py_ssize_t si
+      * 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 */
++           to 1024 bytes. Call it multiple times if more bytes are
++           requested. */
+         n = Py_MIN(size, 1024);
+ #else
+         n = Py_MIN(size, LONG_MAX);
+@@ -161,34 +130,35 @@ py_getrandom(void *buffer, Py_ssize_t si
+ #ifdef HAVE_GETRANDOM
+         if (raise) {
+             Py_BEGIN_ALLOW_THREADS
+-            n = getrandom(buffer, n, flags);
++            n = getrandom(dest, n, flags);
+             Py_END_ALLOW_THREADS
+         }
+         else {
+-            n = getrandom(buffer, n, flags);
++            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 */
++           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, buffer, n, flags);
++            n = syscall(SYS_getrandom, dest, n, flags);
+             Py_END_ALLOW_THREADS
+         }
+         else {
+-            n = syscall(SYS_getrandom, buffer, n, flags);
++            n = syscall(SYS_getrandom, dest, n, flags);
+         }
+ #endif
+ 
+         if (n < 0) {
+-            /* ENOSYS: getrandom() syscall not supported by the kernel (but
+-             * maybe supported by the host which built Python). EPERM:
+-             * getrandom() syscall blocked by SECCOMP or something else. */
++            /* 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
+@@ -202,32 +172,101 @@ py_getrandom(void *buffer, Py_ssize_t si
+             }
+ 
+             if (errno == EINTR) {
+-                if (PyErr_CheckSignals()) {
+-                    if (!raise) {
+-                        Py_FatalError("getrandom() interrupted by a signal");
++                if (raise) {
++                    if (PyErr_CheckSignals()) {
++                        return -1;
+                     }
+-                    return -1;
+                 }
+ 
+-                /* retry getrandom() */
++                /* retry getrandom() if it was interrupted by a signal */
+                 continue;
+             }
+ 
+             if (raise) {
+                 PyErr_SetFromErrno(PyExc_OSError);
+             }
+-            else {
+-                Py_FatalError("getrandom() failed");
++            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. */
++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 += n;
+-        size -= n;
++        buffer += len;
++        size -= len;
+     }
+     return 1;
+ }
+-#endif
++#endif /* defined(HAVE_GETENTROPY) && !defined(sun) */
++
+ 
+ static struct {
+     int fd;
+@@ -235,136 +274,123 @@ static struct {
+     ino_t st_ino;
+ } urandom_cache = { -1 };
+ 
++/* Read random bytes from the /dev/urandom device:
+ 
+-/* 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
+ 
+-   Call Py_FatalError() on error. */
+-static void
+-dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
++   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;
+ 
+-    assert (0 < size);
++    if (raise) {
++        struct _Py_stat_struct st;
+ 
+-#ifdef PY_GETRANDOM
+-    if (py_getrandom(buffer, size, 0) == 1) {
+-        return;
++        if (urandom_cache.fd >= 0) {
++            /* 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 {
++            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);
+     }
+-    /* getrandom() failed with ENOSYS or EPERM,
+-       fall back on reading /dev/urandom */
+-#endif
+-
+-    fd = _Py_open_noraise("/dev/urandom", O_RDONLY);
+-    if (fd < 0) {
+-        Py_FatalError("Failed to open /dev/urandom");
+-    }
+-
+-    while (0 < size)
+-    {
+-        do {
+-            n = read(fd, buffer, (size_t)size);
+-        } while (n < 0 && errno == EINTR);
+-
+-        if (n <= 0) {
+-            /* read() failed or returned 0 bytes */
+-            Py_FatalError("Failed to read bytes from /dev/urandom");
+-            break;
+-        }
+-        buffer += n;
+-        size -= n;
+-    }
+-    close(fd);
+-}
+-
+-/* 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 and return -1 on error. */
+-static int
+-dev_urandom_python(char *buffer, Py_ssize_t size)
+-{
+-    int fd;
+-    Py_ssize_t n;
+-    struct _Py_stat_struct st;
+-#ifdef PY_GETRANDOM
+-    int res;
+-#endif
+-
+-    if (size <= 0)
+-        return 0;
+-
+-#ifdef PY_GETRANDOM
+-    res = py_getrandom(buffer, size, 1);
+-    if (res < 0) {
+-        return -1;
+-    }
+-    if (res == 1) {
+-        return 0;
+-    }
+-    /* getrandom() failed with ENOSYS or EPERM,
+-       fall back on reading /dev/urandom */
+-#endif
+-
+-    if (urandom_cache.fd >= 0) {
+-        /* 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 {
+-        fd = _Py_open("/dev/urandom", O_RDONLY);
++        fd = _Py_open_noraise("/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)) {
++
++        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;
+             }
+-            else {
+-                urandom_cache.fd = fd;
+-                urandom_cache.st_dev = st.st_dev;
+-                urandom_cache.st_ino = st.st_ino;
+-            }
++
++            buffer += n;
++            size -= n;
+         }
++        close(fd);
+     }
+-
+-    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);
+-
+     return 0;
+ }
+ 
+@@ -376,8 +402,8 @@ dev_urandom_close(void)
+         urandom_cache.fd = -1;
+     }
+ }
++#endif /* !MS_WINDOWS */
+ 
+-#endif
+ 
+ /* Fill buffer with pseudo-random bytes generated by a linear congruent
+    generator (LCG):
+@@ -400,29 +426,98 @@ lcg_urandom(unsigned int x0, unsigned ch
+     }
+ }
+ 
++/* 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:
++
++   - 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) {
++        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)
++#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. */
++   Return 0 on success. Raise an exception and return -1 on error. */
+ int
+ _PyOS_URandom(void *buffer, Py_ssize_t size)
+ {
+-    if (size < 0) {
+-        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, 1);
+-#elif defined(PY_GETENTROPY)
+-    return py_getentropy(buffer, size, 0);
+-#else
+-    return dev_urandom_python((char*)buffer, size);
+-#endif
++    return pyurandom(buffer, size, 1);
+ }
+ 
+ void
+@@ -463,13 +558,14 @@ 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");
++        }
+     }
+ }
+ 
+@@ -481,8 +577,6 @@ void
+         CryptReleaseContext(hCryptProv, 0);
+         hCryptProv = 0;
+     }
+-#elif defined(PY_GETENTROPY)
+-    /* nothing to clean */
+ #else
+     dev_urandom_close();
+ #endif
+
diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index 6e41108df6..2a7257b21d 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -325,6 +325,7 @@ data types.")
               (patches (search-patches
                         "python-fix-tests.patch"
                         "python-3.5-fix-tests.patch"
+                        "python-3.5-getentropy-on-old-kernels.patch"
                         "python-3-deterministic-build-info.patch"
                         "python-3-search-paths.patch"))
               (patch-flags '("-p0"))