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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
25static 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
34static 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
44static 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
55static 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
78static 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
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
101
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
136out_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
158int 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
235err_close_ruleset:
236 close(ruleset_fd);
237 return 1;
238}
239
