sandbox-and-launch.c

 1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Sandbox itself and execute another program (in a different mount point).
 4 *
 5 * Used by layout1.umount_sandboxer from fs_test.c
 6 *
 7 * Copyright © 2024-2025 Microsoft Corporation
 8 */
 9
10#define _GNU_SOURCE
11#include <errno.h>
12#include <stdio.h>
13#include <stdlib.h>
14#include <sys/prctl.h>
15#include <unistd.h>
16
17#include "wrappers.h"
18
19int main(int argc, char *argv[])
20{
21	struct landlock_ruleset_attr ruleset_attr = {
22		.scoped = LANDLOCK_SCOPE_SIGNAL,
23	};
24	int pipe_child, pipe_parent, ruleset_fd;
25	char buf;
26
27	/*
28	 * The first argument must be the file descriptor number of a pipe.
29	 * The second argument must be the program to execute.
30	 */
31	if (argc != 4) {
32		fprintf(stderr, "Wrong number of arguments (not three)\n");
33		return 1;
34	}
35
36	pipe_child = atoi(argv[2]);
37	pipe_parent = atoi(argv[3]);
38
39	ruleset_fd =
40		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
41	if (ruleset_fd < 0) {
42		perror("Failed to create ruleset");
43		return 1;
44	}
45
46	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
47		perror("Failed to call prctl()");
48		return 1;
49	}
50
51	if (landlock_restrict_self(ruleset_fd, 0)) {
52		perror("Failed to restrict self");
53		return 1;
54	}
55
56	if (close(ruleset_fd)) {
57		perror("Failed to close ruleset");
58		return 1;
59	}
60
61	/* Signals that we are sandboxed. */
62	errno = 0;
63	if (write(pipe_child, ".", 1) != 1) {
64		perror("Failed to write to the second argument");
65		return 1;
66	}
67
68	/* Waits for the parent to try to umount. */
69	if (read(pipe_parent, &buf, 1) != 1) {
70		perror("Failed to write to the third argument");
71		return 1;
72	}
73
74	/* Shifts arguments. */
75	argv[0] = argv[1];
76	argv[1] = argv[2];
77	argv[2] = argv[3];
78	argv[3] = NULL;
79	execve(argv[0], argv, NULL);
80	perror("Failed to execute the provided binary");
81	return 1;
82}