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Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.

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A pthread_atfork() child handler is used to seeded the PRNG with pid, time
and some stack data.
This commit is contained in:
Christian Heimes 2013-08-21 13:26:34 +02:00
commit 6acbe2aaa3
6 changed files with 123 additions and 0 deletions
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72
Modules/_ssl.c
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@ -18,6 +18,11 @@
#ifdef WITH_THREAD
#include "pythread.h"
#ifdef HAVE_PTHREAD_ATFORK
# include <pthread.h>
#endif
#define PySSL_BEGIN_ALLOW_THREADS_S(save) \
do { if (_ssl_locks_count>0) { (save) = PyEval_SaveThread(); } } while (0)
#define PySSL_END_ALLOW_THREADS_S(save) \
@ -2936,7 +2941,69 @@ 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 */
_PyTime_timeval tp; /* current time */
} seed;
#ifdef WITH_VALGRIND
VALGRIND_MAKE_MEM_DEFINED(seed.stack, sizeof(seed.stack));
#endif
seed.pid = getpid();
_PyTime_gettimeofday(&(seed.tp));
#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 */
PyDoc_STRVAR(PySSL_get_default_verify_paths_doc,
"get_default_verify_paths() -> tuple\n\
@ -3549,5 +3616,10 @@ PyInit__ssl(void)
if (r == NULL || PyModule_AddObject(m, "_OPENSSL_API_VERSION", r))
return NULL;
#ifdef PYSSL_RAND_ATFORK
if (PySSL_RAND_atfork() == -1)
return NULL;
#endif
return m;
}