Issue #25003: On Solaris 11.3 or newer, os.urandom() now uses the getrandom()

function instead of the getentropy() function. The getentropy() function is
blocking to generate very good quality entropy, os.urandom() doesn't need such
high-quality entropy.

1 files changed, 34 insertions, 15 deletions

diff --git a/Python/random.c b/Python/random.c
index ea09e84..1d57b1b 100644
--- a/Python/random.c
+++ b/Python/random.c
@@ -6,7 +6,9 @@
 #  ifdef HAVE_SYS_STAT_H
 #    include <sys/stat.h>
 #  endif
-#  ifdef HAVE_GETRANDOM_SYSCALL
+#  ifdef HAVE_GETRANDOM
+#    include <sys/random.h>
+#  elif defined(HAVE_GETRANDOM_SYSCALL)
 #    include <sys/syscall.h>
 #  endif
 #endif
@@ -70,7 +72,9 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
     return 0;
 }
 
-#elif HAVE_GETENTROPY
+#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.
 
@@ -105,16 +109,19 @@ py_getentropy(unsigned char *buffer, Py_ssize_t size, int fatal)
     return 0;
 }
 
-#else   /* !HAVE_GETENTROPY */
+#else
+
+#if defined(HAVE_GETRANDOM) || defined(HAVE_GETRANDOM_SYSCALL)
+#define PY_GETRANDOM 1
 
-#ifdef HAVE_GETRANDOM_SYSCALL
 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 later */
+    /* Is getrandom() supported by the running kernel?
+     * Need Linux kernel 3.17 or newer, or Solaris 11.3 or newer */
     static int getrandom_works = 1;
-    /* Use /dev/urandom, block if the kernel has no entropy */
+    /* Use non-blocking /dev/urandom device. On Linux at boot, the getrandom()
+     * syscall blocks until /dev/urandom is initialized with enough entropy. */
     const int flags = 0;
     int n;
 
@@ -124,7 +131,18 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
     while (0 < size) {
         errno = 0;
 
-        /* Use syscall() because the libc doesn't expose getrandom() yet, see:
+#ifdef HAVE_GETRANDOM
+        if (raise) {
+            Py_BEGIN_ALLOW_THREADS
+            n = getrandom(buffer, size, flags);
+            Py_END_ALLOW_THREADS
+        }
+        else {
+            n = getrandom(buffer, size, 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
@@ -134,6 +152,7 @@ py_getrandom(void *buffer, Py_ssize_t size, int raise)
         else {
             n = syscall(SYS_getrandom, buffer, size, flags);
         }
+#endif
 
         if (n < 0) {
             if (errno == ENOSYS) {
@@ -182,7 +201,7 @@ dev_urandom_noraise(unsigned char *buffer, Py_ssize_t size)
 
     assert (0 < size);
 
-#ifdef HAVE_GETRANDOM_SYSCALL
+#ifdef PY_GETRANDOM
     if (py_getrandom(buffer, size, 0) == 1)
         return;
     /* getrandom() is not supported by the running kernel, fall back
@@ -218,14 +237,14 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
     int fd;
     Py_ssize_t n;
     struct _Py_stat_struct st;
-#ifdef HAVE_GETRANDOM_SYSCALL
+#ifdef PY_GETRANDOM
     int res;
 #endif
 
     if (size <= 0)
         return 0;
 
-#ifdef HAVE_GETRANDOM_SYSCALL
+#ifdef PY_GETRANDOM
     res = py_getrandom(buffer, size, 1);
     if (res < 0)
         return -1;
@@ -304,7 +323,7 @@ dev_urandom_close(void)
     }
 }
 
-#endif /* HAVE_GETENTROPY */
+#endif
 
 /* Fill buffer with pseudo-random bytes generated by a linear congruent
    generator (LCG):
@@ -345,7 +364,7 @@ _PyOS_URandom(void *buffer, Py_ssize_t size)
 
 #ifdef MS_WINDOWS
     return win32_urandom((unsigned char *)buffer, size, 1);
-#elif HAVE_GETENTROPY
+#elif defined(PY_GETENTROPY)
     return py_getentropy(buffer, size, 0);
 #else
     return dev_urandom_python((char*)buffer, size);
@@ -392,7 +411,7 @@ _PyRandom_Init(void)
     else {
 #ifdef MS_WINDOWS
         (void)win32_urandom(secret, secret_size, 0);
-#elif HAVE_GETENTROPY
+#elif defined(PY_GETENTROPY)
         (void)py_getentropy(secret, secret_size, 1);
 #else
         dev_urandom_noraise(secret, secret_size);
@@ -408,7 +427,7 @@ _PyRandom_Fini(void)
         CryptReleaseContext(hCryptProv, 0);
         hCryptProv = 0;
     }
-#elif HAVE_GETENTROPY
+#elif defined(PY_GETENTROPY)
     /* nothing to clean */
 #else
     dev_urandom_close();