gh-100795: Don't call freeaddrinfo on failure. (GH-101252)

miss-islington · gpshead · sebres · web-flow · commit 81266281073f · 2023-01-23T15:27:41.000-08:00
When getaddrinfo returns an error, the output pointer is in an unknown state Don't call freeaddrinfo on it. See the issue for discussion and details with links to reasoning. _Most_ libc getaddrinfo implementations never modify the output pointer unless they are returning success. (cherry picked from commit b724ac2) Co-authored-by: Gregory P. Smith <greg@krypto.org> Co-authored-by: Sergey G. Brester <github@sebres.de> Co-authored-by: Oleg Iarygin <dralife@yandex.ru>
diff --git a/Misc/NEWS.d/next/Library/2023-01-21-16-50-22.gh-issue-100795.NPMZf7.rst b/Misc/NEWS.d/next/Library/2023-01-21-16-50-22.gh-issue-100795.NPMZf7.rst
@@ -0,0 +1,3 @@
+Avoid potential unexpected ``freeaddrinfo`` call (double free) in :mod:`socket`
+when when a libc ``getaddrinfo()`` implementation leaves garbage in an output
+pointer when returning an error. Original patch by Sergey G. Brester.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
@@ -1053,6 +1053,7 @@ setipaddr(const char *name, struct sockaddr *addr_ret, size_t addr_ret_size, int
            subsequent call to getaddrinfo() does not destroy the
            outcome of the first call. */
         if (error) {
+            res = NULL;  // no-op, remind us that it is invalid; gh-100795
             set_gaierror(error);
             return -1;
         }
@@ -1163,6 +1164,7 @@ setipaddr(const char *name, struct sockaddr *addr_ret, size_t addr_ret_size, int
 #endif
     Py_END_ALLOW_THREADS
     if (error) {
+        res = NULL;  // no-op, remind us that it is invalid; gh-100795
         set_gaierror(error);
         return -1;
     }
@@ -6514,6 +6516,7 @@ socket_getaddrinfo(PyObject *self, PyObject *args, PyObject* kwargs)
     error = getaddrinfo(hptr, pptr, &hints, &res0);
     Py_END_ALLOW_THREADS
     if (error) {
+        res0 = NULL;  // gh-100795
         set_gaierror(error);
         goto err;
     }
@@ -6608,6 +6611,7 @@ socket_getnameinfo(PyObject *self, PyObject *args)
     error = getaddrinfo(hostp, pbuf, &hints, &res);
     Py_END_ALLOW_THREADS
     if (error) {
+        res = NULL;  // gh-100795
         set_gaierror(error);
         goto fail;
     }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Avoid potential unexpected ``freeaddrinfo`` call (double free) in :mod:`socket`
	`2`	+when when a libc ``getaddrinfo()`` implementation leaves garbage in an output
	`3`	`+pointer when returning an error. Original patch by Sergey G. Brester.`