[LTP] [PATCH 4/4] syscalls/add_key03: new test for forging user keyrings

Eric Biggers
2017-10-10T17:51:20Z

Add a test for a bug which allowed a user to create the user and user
session keyrings for another user.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
runtest/syscalls | 1 +
testcases/kernel/syscalls/.gitignore | 1 +
testcases/kernel/syscalls/add_key/add_key03.c | 122 ++++++++++++++++++++++++++
3 files changed, 124 insertions(+)
create mode 100644 testcases/kernel/syscalls/add_key/add_key03.c

diff --git a/runtest/syscalls b/runtest/syscalls
index 649dbfa6c..0d2254393 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -13,6 +13,7 @@ acct01 acct01

add_key01 add_key01
add_key02 add_key02
+add_key03 add_key03

adjtimex01 adjtimex01
adjtimex02 adjtimex02
diff --git a/testcases/kernel/syscalls/.gitignore b/testcases/kernel/syscalls/.gitignore
index 53ad7ca2b..7dea3b2c7 100644
--- a/testcases/kernel/syscalls/.gitignore
+++ b/testcases/kernel/syscalls/.gitignore
@@ -8,6 +8,7 @@
/acct/acct01
/add_key/add_key01
/add_key/add_key02
+/add_key/add_key03
/adjtimex/adjtimex01
/adjtimex/adjtimex02
/alarm/alarm01
diff --git a/testcases/kernel/syscalls/add_key/add_key03.c b/testcases/kernel/syscalls/add_key/add_key03.c
new file mode 100644
index 000000000..8c68f8635
--- /dev/null
+++ b/testcases/kernel/syscalls/add_key/add_key03.c
@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2017 Google, Inc.
+ *
+ * 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 2 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/>.
+ */
+
+/*
+ * Regression test for commit 237bbd29f7a0 ("KEYS: prevent creating a different
+ * user's keyrings"). The bug allowed any random user to create a keyring named
+ * "_uid.$UID" (or "_uid_ses.$UID"), and it would become the user keyring (or
+ * user session keyring) for user $UID, provided that it hadn't already been
+ * created.
+ *
+ * This test must be run as root so that it has permission to switch to another
+ * user ID and check whether the keyrings are wrong. However, the underlying
+ * bug is actually reachable/exploitable by a non-root user.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "tst_test.h"
+#include "lapi/keyctl.h"
+
+static key_serial_t create_keyring(const char *description)
+{
+ TEST(add_key("keyring", description, NULL, 0,
+ KEY_SPEC_PROCESS_KEYRING));
+ if (TEST_RETURN < 0) {
+ tst_brk(TBROK | TTERRNO,
+ "unable to create keyring '%s'", description);
+ }
+ return TEST_RETURN;
+}
+
+static key_serial_t get_keyring_id(key_serial_t special_id)
+{
+ TEST(keyctl(KEYCTL_GET_KEYRING_ID, special_id, 1));
+ if (TEST_RETURN < 0) {
+ tst_brk(TBROK | TTERRNO,
+ "unable to get ID of keyring %d", special_id);
+ }
+ return TEST_RETURN;
+}
+
+static void unlink_keyring(key_serial_t id)
+{
+ TEST(keyctl(KEYCTL_UNLINK, id, KEY_SPEC_PROCESS_KEYRING));
+ if (TEST_RETURN < 0) {
+ tst_brk(TBROK | TTERRNO,
+ "unable to unlink the keyring we created");
+ }
+}
+
+static void do_test(void)
+{
+ int i;
+
+ /*
+ * Try with multiple user IDs before reporting success. By chance, some
+ * users may already have an existing user keyring; the bug will not be
+ * reproducible for them.
+ */
+ for (i = 0; i < 10; i++) {
+ char description[32];
+ uid_t uid;
+ key_serial_t fake_user_keyring;
+ key_serial_t fake_user_session_keyring;
+
+ uid = rand();
+ if (uid == 0)
+ continue;
+
+ sprintf(description, "_uid.%u", uid);
+ fake_user_keyring = create_keyring(description);
+ sprintf(description, "_uid_ses.%u", uid);
+ fake_user_session_keyring = create_keyring(description);
+
+ TEST(setreuid(uid, 0));
+ if (TEST_RETURN < 0) {
+ tst_brk(TBROK | TTERRNO,
+ "unable to set real uid to %u", uid);
+ }
+
+ if (fake_user_keyring == get_keyring_id(KEY_SPEC_USER_KEYRING)) {
+ tst_brk(TFAIL,
+ "created user keyring for another user");
+ }
+
+ if (fake_user_session_keyring ==
+ get_keyring_id(KEY_SPEC_USER_SESSION_KEYRING)) {
+ tst_brk(TFAIL,
+ "created user session keyring for another user");
+ }
+
+ TEST(setreuid(0, 0));
+ if (TEST_RETURN < 0)
+ tst_brk(TBROK | TTERRNO, "unable to reset real uid");
+ uid++;
+
+ unlink_keyring(fake_user_keyring);
+ unlink_keyring(fake_user_session_keyring);
+ }
+ tst_res(TPASS, "expectedly could not create another user's keyrings");
+}
+
+static struct tst_test test = {
+ .test_all = do_test,
+ .needs_root = 1,
+};
--
2.14.2.920.gcf0c67979c-goog