[Python-checkins] cpython (3.5): Cleanup random.c

Tue Sep 20 16:52:41 EDT 2016

https://hg.python.org/cpython/rev/41e9e711b9b5
changeset: 103971:41e9e711b9b5
branch: 3.5
parent: 103968:de32a2426713
user: Victor Stinner <victor.stinner at gmail.com>
date: Tue Sep 20 22:26:18 2016 +0200
summary:
 Cleanup random.c
Issue #27955: modify py_getrnadom() and dev_urandom()
* Add comments from Python 3.7
* PEP 7 style: add {...}
files:
 Python/random.c | 81 ++++++++++++++++++++++++------------
 1 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/Python/random.c b/Python/random.c
--- a/Python/random.c
+++ b/Python/random.c
@@ -119,11 +119,20 @@
 #if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
 #define PY_GETRANDOM 1
 
+/* Call getrandom()
+ - Return 1 on success
+ - Return 0 if getrandom() syscall is not available (failed with ENOSYS)
+ 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:
+ 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)
 {
- /* 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()
+ failed 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
@@ -134,8 +143,9 @@
 const int flags = GRND_NONBLOCK;
 long n;
 
- if (!getrandom_works)
+ if (!getrandom_works) {
 return 0;
+ }
 
 while (0 < size) {
 #ifdef sun
@@ -171,36 +181,42 @@
 #endif
 
 if (n < 0) {
+ /* ENOSYS: getrandom() syscall not supported by the kernel (but
+ * maybe supported by the host which built Python). */
 if (errno == ENOSYS) {
 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(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 (PyErr_CheckSignals()) {
- if (!raise)
+ if (!raise) {
 Py_FatalError("getrandom() interrupted by a signal");
+ }
 return -1;
 }
+
 /* retry getrandom() */
 continue;
 }
 
- if (raise)
+ if (raise) {
 PyErr_SetFromErrno(PyExc_OSError);
- else
+ }
+ else {
 Py_FatalError("getrandom() failed");
+ }
 return -1;
 }
 
@@ -218,7 +234,9 @@
 } urandom_cache = { -1 };
 
 
-/* Read size bytes from /dev/urandom into buffer.
+/* Read 'size' random bytes from py_getrandom(). Fall back on reading from
+ /dev/urandom if getrandom() is not available.
+
 Call Py_FatalError() on error. */
 static void
 dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
@@ -229,24 +247,26 @@
 assert (0 < size);
 
 #ifdef PY_GETRANDOM
- if (py_getrandom(buffer, size, 0) == 1)
+ if (py_getrandom(buffer, size, 0) == 1) {
 return;
- /* getrandom() is not supported by the running kernel, fall back
- * on reading /dev/urandom */
+ }
+ /* getrandom() failed with ENOSYS,
+ fall back on reading /dev/urandom */
 #endif
 
 fd = _Py_open_noraise("/dev/urandom", O_RDONLY);
- if (fd < 0)
+ 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)
- {
- /* stop on error or if read(size) returned 0 */
+
+ if (n <= 0) {
+ /* read() failed or returned 0 bytes */
 Py_FatalError("Failed to read bytes from /dev/urandom");
 break;
 }
@@ -256,8 +276,10 @@
 close(fd);
 }
 
-/* Read size bytes from /dev/urandom into buffer.
- Return 0 on success, raise an exception and return -1 on error. */
+/* 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)
 {
@@ -273,12 +295,14 @@
 
 #ifdef PY_GETRANDOM
 res = py_getrandom(buffer, size, 1);
- if (res < 0)
+ if (res < 0) {
 return -1;
- if (res == 1)
+ }
+ if (res == 1) {
 return 0;
- /* getrandom() is not supported by the running kernel, fall back
- * on reading /dev/urandom */
+ }
+ /* getrandom() failed with ENOSYS,
+ fall back on reading /dev/urandom */
 #endif
 
 if (urandom_cache.fd >= 0) {
@@ -325,8 +349,9 @@
 
 do {
 n = _Py_read(fd, buffer, (size_t)size);
- if (n == -1)
+ if (n == -1) {
 return -1;
+ }
 if (n == 0) {
 PyErr_Format(PyExc_RuntimeError,
 "Failed to read %zi bytes from /dev/urandom",
-- 
Repository URL: https://hg.python.org/cpython
