lib:util: Add support to keep talloc chunks secret

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlet <abartlet@samba.org>

lib/util/talloc_keep_secret.c

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2019      Andreas Schneider <asn@samba.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "includes.h"
+#include "talloc_keep_secret.h"
+
+static int talloc_keep_secret_destructor(void *ptr)
+{
+	size_t size = talloc_get_size(ptr);
+
+	if (unlikely(size == 0)) {
+		return 0;
+	}
+
+	memset_s(ptr, size, 0, size);
+
+	return 0;
+}
+
+void _talloc_keep_secret(void *ptr, const char *name)
+{
+	size_t size;
+
+	if (unlikely(ptr == NULL)) {
+#ifdef DEVELOPER
+		smb_panic("Invalid talloc pointer");
+#endif
+		return;
+	}
+
+	size = talloc_get_size(ptr);
+	if (unlikely(size == 0)) {
+		return;
+	}
+
+	talloc_set_name_const(ptr, name);
+	talloc_set_destructor(ptr, talloc_keep_secret_destructor);
+}

lib/util/talloc_keep_secret.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2019      Andreas Schneider <asn@samba.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _TALLOC_KEEP_SECRET_H
+#define _TALLOC_KEEP_SECRET_H
+
+#ifdef DOXYGEN
+/**
+ * @brief Keep the memory secret when freeing.
+ *
+ * This can be used to define memory as secret. For example memory which holds
+ * passwords or other secrets like session keys. The memory will be zeroed
+ * before is being freed.
+ *
+ * If you duplicate memory, e.g. using talloc_strdup() or talloc_asprintf() you
+ * need to call talloc_keep_secret() on the newly allocated memory too!
+ *
+ * @param[in]  ptr      The talloc chunk to mark as secure.
+ *
+ * @warning Do not use this in combination with talloc_realloc().
+ */
+void talloc_keep_secret(const void *ptr);
+#else
+#define talloc_keep_secret(ptr) _talloc_keep_secret(ptr, #ptr);
+void _talloc_keep_secret(void *ptr, const char *name);
+#endif
+
+#endif /* _TALLOC_KEEP_SECRET_H */

lib/util/wscript_build

@@ -115,16 +115,34 @@ else:
                      install=False)
 
     bld.SAMBA_LIBRARY('samba-util',
-                  source='''talloc_stack.c smb_threads.c
-                    rbtree.c rfc1738.c system.c getpass.c
-                    genrand_util.c fsusage.c
-                    params.c util_id.c util_net.c
-                    util_strlist_v3.c util_paths.c
-                    idtree_random.c base64.c
-                    util_str.c util_str_common.c ms_fnmatch.c
-                    server_id.c dprintf.c
-                    tevent_debug.c memcache.c unix_match.c tfork.c
-                    tftw.c''',
+                  source='''
+                         base64.c
+                         dprintf.c
+                         fsusage.c
+                         genrand_util.c
+                         getpass.c
+                         idtree_random.c
+                         memcache.c
+                         ms_fnmatch.c
+                         params.c
+                         rbtree.c
+                         rfc1738.c
+                         server_id.c
+                         smb_threads.c
+                         system.c
+                         talloc_keep_secret.c
+                         talloc_stack.c
+                         tevent_debug.c
+                         tfork.c
+                         tftw.c
+                         unix_match.c
+                         util_id.c
+                         util_net.c
+                         util_paths.c
+                         util_str.c
+                         util_str_common.c
+                         util_strlist_v3.c
+                         ''',
                   deps='samba-util-core DYNCONFIG close-low-fd tiniparser genrand util_str_hex',
                   public_deps='talloc tevent execinfo pthread LIBCRYPTO charset util_setid',
                   public_headers='''