1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (c) 2017 Google, Inc.
4 */
5
6/*
7 * Regression test for commit 237bbd29f7a0 ("KEYS: prevent creating a different
8 * user's keyrings").  The bug allowed any random user to create a keyring named
9 * "_uid.$UID" (or "_uid_ses.$UID"), and it would become the user keyring (or
10 * user session keyring) for user $UID, provided that it hadn't already been
11 * created.
12 *
13 * This test must be run as root so that it has permission to switch to another
14 * user ID and check whether the keyrings are wrong.  However, the underlying
15 * bug is actually reachable/exploitable by a non-root user.
16 */
17
18#include <errno.h>
19#include <pwd.h>
20#include <stdio.h>
21
22#include "tst_test.h"
23#include "lapi/keyctl.h"
24
25static key_serial_t create_keyring(const char *description)
26{
27	TEST(add_key("keyring", description, NULL, 0,
28		     KEY_SPEC_PROCESS_KEYRING));
29	if (TST_RET < 0) {
30		tst_brk(TBROK | TTERRNO,
31			"unable to create keyring '%s'", description);
32	}
33	return TST_RET;
34}
35
36static key_serial_t get_keyring_id(key_serial_t special_id)
37{
38	TEST(keyctl(KEYCTL_GET_KEYRING_ID, special_id, 1));
39	if (TST_RET < 0) {
40		tst_brk(TBROK | TTERRNO,
41			"unable to get ID of keyring %d", special_id);
42	}
43	return TST_RET;
44}
45
46static void do_test(void)
47{
48	uid_t uid = 1;
49	char description[32];
50	key_serial_t fake_user_keyring;
51	key_serial_t fake_user_session_keyring;
52
53	/*
54	 * We need a user to forge the keyrings for.  But the bug is not
55	 * reproducible for a UID which already has its keyrings, so find an
56	 * unused UID.  Note that it would be better to directly check for the
57	 * presence of the UID's keyrings than to search the passwd file.
58	 * However, that's not easy to do given that even if we assumed the UID
59	 * temporarily to check, KEYCTL_GET_KEYRING_ID for the user and user
60	 * session keyrings will create them rather than failing (even if the
61	 * 'create' argument is 0).
62	 */
63	while (getpwuid(uid))
64		uid++;
65
66	sprintf(description, "_uid.%u", uid);
67	fake_user_keyring = create_keyring(description);
68	sprintf(description, "_uid_ses.%u", uid);
69	fake_user_session_keyring = create_keyring(description);
70
71	SAFE_SETUID(uid);
72
73	if (fake_user_keyring == get_keyring_id(KEY_SPEC_USER_KEYRING))
74		tst_brk(TFAIL, "created user keyring for another user");
75
76	if (fake_user_session_keyring ==
77	    get_keyring_id(KEY_SPEC_USER_SESSION_KEYRING))
78		tst_brk(TFAIL, "created user session keyring for another user");
79
80	tst_res(TPASS, "expectedly could not create another user's keyrings");
81}
82
83static struct tst_test test = {
84	.test_all = do_test,
85	.needs_root = 1,
86	.tags = (const struct tst_tag[]) {
87		{"linux-git", "237bbd29f7a0"},
88		{}
89	}
90};
91