Merge tag 'gpio-updates-for-v5.14-rc5' of git://git.kernel.org/pub/scm/linux/kernel...
[linux-2.6-microblaze.git] / samples / landlock / sandboxer.c
1 // SPDX-License-Identifier: BSD-3-Clause
2 /*
3  * Simple Landlock sandbox manager able to launch a process restricted by a
4  * user-defined filesystem access control policy.
5  *
6  * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
7  * Copyright © 2020 ANSSI
8  */
9
10 #define _GNU_SOURCE
11 #include <errno.h>
12 #include <fcntl.h>
13 #include <linux/landlock.h>
14 #include <linux/prctl.h>
15 #include <stddef.h>
16 #include <stdio.h>
17 #include <stdlib.h>
18 #include <string.h>
19 #include <sys/prctl.h>
20 #include <sys/stat.h>
21 #include <sys/syscall.h>
22 #include <unistd.h>
23
24 #ifndef landlock_create_ruleset
25 static inline int landlock_create_ruleset(
26                 const struct landlock_ruleset_attr *const attr,
27                 const size_t size, const __u32 flags)
28 {
29         return syscall(__NR_landlock_create_ruleset, attr, size, flags);
30 }
31 #endif
32
33 #ifndef landlock_add_rule
34 static inline int landlock_add_rule(const int ruleset_fd,
35                 const enum landlock_rule_type rule_type,
36                 const void *const rule_attr, const __u32 flags)
37 {
38         return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type,
39                         rule_attr, flags);
40 }
41 #endif
42
43 #ifndef landlock_restrict_self
44 static inline int landlock_restrict_self(const int ruleset_fd,
45                 const __u32 flags)
46 {
47         return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
48 }
49 #endif
50
51 #define ENV_FS_RO_NAME "LL_FS_RO"
52 #define ENV_FS_RW_NAME "LL_FS_RW"
53 #define ENV_PATH_TOKEN ":"
54
55 static int parse_path(char *env_path, const char ***const path_list)
56 {
57         int i, num_paths = 0;
58
59         if (env_path) {
60                 num_paths++;
61                 for (i = 0; env_path[i]; i++) {
62                         if (env_path[i] == ENV_PATH_TOKEN[0])
63                                 num_paths++;
64                 }
65         }
66         *path_list = malloc(num_paths * sizeof(**path_list));
67         for (i = 0; i < num_paths; i++)
68                 (*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
69
70         return num_paths;
71 }
72
73 #define ACCESS_FILE ( \
74         LANDLOCK_ACCESS_FS_EXECUTE | \
75         LANDLOCK_ACCESS_FS_WRITE_FILE | \
76         LANDLOCK_ACCESS_FS_READ_FILE)
77
78 static int populate_ruleset(
79                 const char *const env_var, const int ruleset_fd,
80                 const __u64 allowed_access)
81 {
82         int num_paths, i, ret = 1;
83         char *env_path_name;
84         const char **path_list = NULL;
85         struct landlock_path_beneath_attr path_beneath = {
86                 .parent_fd = -1,
87         };
88
89         env_path_name = getenv(env_var);
90         if (!env_path_name) {
91                 /* Prevents users to forget a setting. */
92                 fprintf(stderr, "Missing environment variable %s\n", env_var);
93                 return 1;
94         }
95         env_path_name = strdup(env_path_name);
96         unsetenv(env_var);
97         num_paths = parse_path(env_path_name, &path_list);
98         if (num_paths == 1 && path_list[0][0] == '\0') {
99                 /*
100                  * Allows to not use all possible restrictions (e.g. use
101                  * LL_FS_RO without LL_FS_RW).
102                  */
103                 ret = 0;
104                 goto out_free_name;
105         }
106
107         for (i = 0; i < num_paths; i++) {
108                 struct stat statbuf;
109
110                 path_beneath.parent_fd = open(path_list[i], O_PATH |
111                                 O_CLOEXEC);
112                 if (path_beneath.parent_fd < 0) {
113                         fprintf(stderr, "Failed to open \"%s\": %s\n",
114                                         path_list[i],
115                                         strerror(errno));
116                         goto out_free_name;
117                 }
118                 if (fstat(path_beneath.parent_fd, &statbuf)) {
119                         close(path_beneath.parent_fd);
120                         goto out_free_name;
121                 }
122                 path_beneath.allowed_access = allowed_access;
123                 if (!S_ISDIR(statbuf.st_mode))
124                         path_beneath.allowed_access &= ACCESS_FILE;
125                 if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
126                                         &path_beneath, 0)) {
127                         fprintf(stderr, "Failed to update the ruleset with \"%s\": %s\n",
128                                         path_list[i], strerror(errno));
129                         close(path_beneath.parent_fd);
130                         goto out_free_name;
131                 }
132                 close(path_beneath.parent_fd);
133         }
134         ret = 0;
135
136 out_free_name:
137         free(env_path_name);
138         return ret;
139 }
140
141 #define ACCESS_FS_ROUGHLY_READ ( \
142         LANDLOCK_ACCESS_FS_EXECUTE | \
143         LANDLOCK_ACCESS_FS_READ_FILE | \
144         LANDLOCK_ACCESS_FS_READ_DIR)
145
146 #define ACCESS_FS_ROUGHLY_WRITE ( \
147         LANDLOCK_ACCESS_FS_WRITE_FILE | \
148         LANDLOCK_ACCESS_FS_REMOVE_DIR | \
149         LANDLOCK_ACCESS_FS_REMOVE_FILE | \
150         LANDLOCK_ACCESS_FS_MAKE_CHAR | \
151         LANDLOCK_ACCESS_FS_MAKE_DIR | \
152         LANDLOCK_ACCESS_FS_MAKE_REG | \
153         LANDLOCK_ACCESS_FS_MAKE_SOCK | \
154         LANDLOCK_ACCESS_FS_MAKE_FIFO | \
155         LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
156         LANDLOCK_ACCESS_FS_MAKE_SYM)
157
158 int main(const int argc, char *const argv[], char *const *const envp)
159 {
160         const char *cmd_path;
161         char *const *cmd_argv;
162         int ruleset_fd;
163         struct landlock_ruleset_attr ruleset_attr = {
164                 .handled_access_fs = ACCESS_FS_ROUGHLY_READ |
165                         ACCESS_FS_ROUGHLY_WRITE,
166         };
167
168         if (argc < 2) {
169                 fprintf(stderr, "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
170                                 ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
171                 fprintf(stderr, "Launch a command in a restricted environment.\n\n");
172                 fprintf(stderr, "Environment variables containing paths, "
173                                 "each separated by a colon:\n");
174                 fprintf(stderr, "* %s: list of paths allowed to be used in a read-only way.\n",
175                                 ENV_FS_RO_NAME);
176                 fprintf(stderr, "* %s: list of paths allowed to be used in a read-write way.\n",
177                                 ENV_FS_RW_NAME);
178                 fprintf(stderr, "\nexample:\n"
179                                 "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
180                                 "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
181                                 "%s bash -i\n",
182                                 ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
183                 return 1;
184         }
185
186         ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
187         if (ruleset_fd < 0) {
188                 const int err = errno;
189
190                 perror("Failed to create a ruleset");
191                 switch (err) {
192                 case ENOSYS:
193                         fprintf(stderr, "Hint: Landlock is not supported by the current kernel. "
194                                         "To support it, build the kernel with "
195                                         "CONFIG_SECURITY_LANDLOCK=y and prepend "
196                                         "\"landlock,\" to the content of CONFIG_LSM.\n");
197                         break;
198                 case EOPNOTSUPP:
199                         fprintf(stderr, "Hint: Landlock is currently disabled. "
200                                         "It can be enabled in the kernel configuration by "
201                                         "prepending \"landlock,\" to the content of CONFIG_LSM, "
202                                         "or at boot time by setting the same content to the "
203                                         "\"lsm\" kernel parameter.\n");
204                         break;
205                 }
206                 return 1;
207         }
208         if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
209                                 ACCESS_FS_ROUGHLY_READ)) {
210                 goto err_close_ruleset;
211         }
212         if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd,
213                                 ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE)) {
214                 goto err_close_ruleset;
215         }
216         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
217                 perror("Failed to restrict privileges");
218                 goto err_close_ruleset;
219         }
220         if (landlock_restrict_self(ruleset_fd, 0)) {
221                 perror("Failed to enforce ruleset");
222                 goto err_close_ruleset;
223         }
224         close(ruleset_fd);
225
226         cmd_path = argv[1];
227         cmd_argv = argv + 1;
228         execvpe(cmd_path, cmd_argv, envp);
229         fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
230                         strerror(errno));
231         fprintf(stderr, "Hint: access to the binary, the interpreter or "
232                         "shared libraries may be denied.\n");
233         return 1;
234
235 err_close_ruleset:
236         close(ruleset_fd);
237         return 1;
238 }