1 // SPDX-License-Identifier: GPL-2.0
2 
3 /*
4  * Copyright (C) 2020 Google LLC.
5  */
6 
7 #include <test_progs.h>
8 #include <linux/limits.h>
9 
10 #include "bprm_opts.skel.h"
11 #include "network_helpers.h"
12 #include "task_local_storage_helpers.h"
13 
14 static const char * const bash_envp[] = { "TMPDIR=shouldnotbeset", NULL };
15 
update_storage(int map_fd,int secureexec)16 static int update_storage(int map_fd, int secureexec)
17 {
18 	int task_fd, ret = 0;
19 
20 	task_fd = sys_pidfd_open(getpid(), 0);
21 	if (task_fd < 0)
22 		return errno;
23 
24 	ret = bpf_map_update_elem(map_fd, &task_fd, &secureexec, BPF_NOEXIST);
25 	if (ret)
26 		ret = errno;
27 
28 	close(task_fd);
29 	return ret;
30 }
31 
run_set_secureexec(int map_fd,int secureexec)32 static int run_set_secureexec(int map_fd, int secureexec)
33 {
34 	int child_pid, child_status, ret, null_fd;
35 
36 	child_pid = fork();
37 	if (child_pid == 0) {
38 		null_fd = open("/dev/null", O_WRONLY);
39 		if (null_fd == -1)
40 			exit(errno);
41 		dup2(null_fd, STDOUT_FILENO);
42 		dup2(null_fd, STDERR_FILENO);
43 		close(null_fd);
44 
45 		/* Ensure that all executions from hereon are
46 		 * secure by setting a local storage which is read by
47 		 * the bprm_creds_for_exec hook and sets bprm->secureexec.
48 		 */
49 		ret = update_storage(map_fd, secureexec);
50 		if (ret)
51 			exit(ret);
52 
53 		/* If the binary is executed with securexec=1, the dynamic
54 		 * loader ingores and unsets certain variables like LD_PRELOAD,
55 		 * TMPDIR etc. TMPDIR is used here to simplify the example, as
56 		 * LD_PRELOAD requires a real .so file.
57 		 *
58 		 * If the value of TMPDIR is set, the bash command returns 10
59 		 * and if the value is unset, it returns 20.
60 		 */
61 		execle("/bin/bash", "bash", "-c",
62 		       "[[ -z \"${TMPDIR}\" ]] || exit 10 && exit 20", NULL,
63 		       bash_envp);
64 		exit(errno);
65 	} else if (child_pid > 0) {
66 		waitpid(child_pid, &child_status, 0);
67 		ret = WEXITSTATUS(child_status);
68 
69 		/* If a secureexec occurred, the exit status should be 20 */
70 		if (secureexec && ret == 20)
71 			return 0;
72 
73 		/* If normal execution happened, the exit code should be 10 */
74 		if (!secureexec && ret == 10)
75 			return 0;
76 	}
77 
78 	return -EINVAL;
79 }
80 
test_test_bprm_opts(void)81 void test_test_bprm_opts(void)
82 {
83 	int err, duration = 0;
84 	struct bprm_opts *skel = NULL;
85 
86 	skel = bprm_opts__open_and_load();
87 	if (CHECK(!skel, "skel_load", "skeleton failed\n"))
88 		goto close_prog;
89 
90 	err = bprm_opts__attach(skel);
91 	if (CHECK(err, "attach", "attach failed: %d\n", err))
92 		goto close_prog;
93 
94 	/* Run the test with the secureexec bit unset */
95 	err = run_set_secureexec(bpf_map__fd(skel->maps.secure_exec_task_map),
96 				 0 /* secureexec */);
97 	if (CHECK(err, "run_set_secureexec:0", "err = %d\n", err))
98 		goto close_prog;
99 
100 	/* Run the test with the secureexec bit set */
101 	err = run_set_secureexec(bpf_map__fd(skel->maps.secure_exec_task_map),
102 				 1 /* secureexec */);
103 	if (CHECK(err, "run_set_secureexec:1", "err = %d\n", err))
104 		goto close_prog;
105 
106 close_prog:
107 	bprm_opts__destroy(skel);
108 }
109