From: Christian Heimes <christian@cheimes.de>
Date: Wed, 21 Aug 2013 11:26:05 +0000 (+0200)
Subject: Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.
X-Git-Tag: v2.7.6rc1~214
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0d604cf65e66f20fca345c4da4526552622a2501;p=thirdparty%2FPython%2Fcpython.git

Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.
A pthread_atfork() child handler is used to seeded the PRNG with pid, time
and some stack data.
---

diff --git a/Misc/NEWS b/Misc/NEWS
index 4c39da3748fc..04317f839993 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -32,6 +32,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.
+  A pthread_atfork() child handler is used to seeded the PRNG with pid, time
+  and some stack data.
+
 - Issue #8865: Concurrent invocation of select.poll.poll() now raises a
   RuntimeError exception.  Patch by Christian Schubert.
 
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index b3eb6ec339bb..1c769edb0913 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -18,6 +18,11 @@
 
 #ifdef WITH_THREAD
 #include "pythread.h"
+
+#ifdef HAVE_PTHREAD_ATFORK
+#  include <pthread.h>
+#endif
+
 #define PySSL_BEGIN_ALLOW_THREADS { \
             PyThreadState *_save = NULL;  \
             if (_ssl_locks_count>0) {_save = PyEval_SaveThread();}
@@ -1621,7 +1626,69 @@ Queries the entropy gather daemon (EGD) on the socket named by 'path'.\n\
 Returns number of bytes read.  Raises SSLError if connection to EGD\n\
 fails or if it does not provide enough data to seed PRNG.");
 
+/* Seed OpenSSL's PRNG at fork(), http://bugs.python.org/issue18747
+ *
+ * The child handler seeds the PRNG from pseudo-random data like pid, the
+ * current time (nanoseconds, miliseconds or seconds) and an uninitialized
+ * array. The array contains stack variables that are impossible to predict
+ * on most systems, e.g. function return address (subject to ASLR), the
+ * stack protection canary and automatic variables.
+ * The code is inspired by Apache's ssl_rand_seed() function.
+ *
+ * Note:
+ * The code uses pthread_atfork() until Python has a proper atfork API. The
+ * handlers are not removed from the child process.
+ */
+
+#if defined(HAVE_PTHREAD_ATFORK) && defined(WITH_THREAD)
+#define PYSSL_RAND_ATFORK 1
+
+static void
+PySSL_RAND_atfork_child(void)
+{
+    struct {
+        char stack[128];    /* uninitialized (!) stack data, 128 is an
+                               arbitrary number. */
+        pid_t pid;          /* current pid */
+        time_t time;        /* current time */
+    } seed;
+
+#ifdef WITH_VALGRIND
+    VALGRIND_MAKE_MEM_DEFINED(seed.stack, sizeof(seed.stack));
 #endif
+    seed.pid = getpid();
+    seed.time = time(NULL);
+
+#if 0
+    fprintf(stderr, "PySSL_RAND_atfork_child() seeds %i bytes in pid %i\n",
+            (int)sizeof(seed), seed.pid);
+#endif
+    RAND_add((unsigned char *)&seed, sizeof(seed), 0.0);
+}
+
+static int
+PySSL_RAND_atfork(void)
+{
+    static int registered = 0;
+    int retval;
+
+    if (registered)
+        return 0;
+
+    retval = pthread_atfork(NULL,                     /* prepare */
+                            NULL,                     /* parent */
+                            PySSL_RAND_atfork_child); /* child */
+    if (retval != 0) {
+        PyErr_SetFromErrno(PyExc_OSError);
+        return -1;
+    }
+    registered = 1;
+    return 0;
+}
+#endif /* HAVE_PTHREAD_ATFORK */
+
+#endif /* HAVE_OPENSSL_RAND */
+
 
 /* List of functions exported by this module. */
 
@@ -1833,4 +1900,9 @@ init_ssl(void)
     r = PyString_FromString(SSLeay_version(SSLEAY_VERSION));
     if (r == NULL || PyModule_AddObject(m, "OPENSSL_VERSION", r))
         return;
+
+#ifdef PYSSL_RAND_ATFORK
+    if (PySSL_RAND_atfork() == -1)
+        return;
+#endif
 }
diff --git a/configure b/configure
index 5f376af77567..68e47842b564 100755
--- a/configure
+++ b/configure
@@ -9627,6 +9627,17 @@ $as_echo "#define HAVE_BROKEN_PTHREAD_SIGMASK 1" >>confdefs.h
 
             ;;
         esac
+fi
+done
+
+      for ac_func in pthread_atfork
+do :
+  ac_fn_c_check_func "$LINENO" "pthread_atfork" "ac_cv_func_pthread_atfork"
+if test "x$ac_cv_func_pthread_atfork" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_PTHREAD_ATFORK 1
+_ACEOF
+
 fi
 done
 
diff --git a/configure.ac b/configure.ac
index b4ed0107a83d..d922bc7cb176 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2569,6 +2569,7 @@ if test "$posix_threads" = "yes"; then
             [Define if pthread_sigmask() does not work on your system.])
             ;;
         esac])
+      AC_CHECK_FUNCS(pthread_atfork)
 fi
 
 
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 65df68aed9f6..8ac017e2383e 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -520,6 +520,9 @@
 /* Define if you have GNU PTH threads. */
 #undef HAVE_PTH
 
+/* Define to 1 if you have the `pthread_atfork' function. */
+#undef HAVE_PTHREAD_ATFORK
+
 /* Defined for Solaris 2.6 bug in pthread header. */
 #undef HAVE_PTHREAD_DESTRUCTOR