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![Mickaël Salaün](/assets/img/avatar_default.png)
Let's follow a consistent and documented coding style. Everything may not be to our liking but it is better than tacit knowledge. Moreover, this will help maintain style consistency between different developers. This contains only whitespace changes. Automatically formatted with: clang-format-14 -i samples/landlock/*.[ch] Link: https://lore.kernel.org/r/20220506160513.523257-8-mic@digikod.net Cc: stable@vger.kernel.org Signed-off-by: Mickaël Salaün <mic@digikod.net>
255 lines
6.6 KiB
C
255 lines
6.6 KiB
C
// SPDX-License-Identifier: BSD-3-Clause
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/*
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* Simple Landlock sandbox manager able to launch a process restricted by a
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* user-defined filesystem access control policy.
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*
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* Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2020 ANSSI
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*/
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#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/landlock.h>
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#include <linux/prctl.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/prctl.h>
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#include <sys/stat.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#ifndef landlock_create_ruleset
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static inline int
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landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
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const size_t size, const __u32 flags)
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{
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return syscall(__NR_landlock_create_ruleset, attr, size, flags);
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}
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#endif
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#ifndef landlock_add_rule
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static inline int landlock_add_rule(const int ruleset_fd,
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const enum landlock_rule_type rule_type,
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const void *const rule_attr,
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const __u32 flags)
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{
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return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
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flags);
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}
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#endif
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#ifndef landlock_restrict_self
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static inline int landlock_restrict_self(const int ruleset_fd,
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const __u32 flags)
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{
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return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
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}
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#endif
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#define ENV_FS_RO_NAME "LL_FS_RO"
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#define ENV_FS_RW_NAME "LL_FS_RW"
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#define ENV_PATH_TOKEN ":"
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static int parse_path(char *env_path, const char ***const path_list)
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{
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int i, num_paths = 0;
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if (env_path) {
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num_paths++;
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for (i = 0; env_path[i]; i++) {
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if (env_path[i] == ENV_PATH_TOKEN[0])
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num_paths++;
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}
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}
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*path_list = malloc(num_paths * sizeof(**path_list));
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for (i = 0; i < num_paths; i++)
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(*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
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return num_paths;
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}
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/* clang-format off */
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#define ACCESS_FILE ( \
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LANDLOCK_ACCESS_FS_EXECUTE | \
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LANDLOCK_ACCESS_FS_WRITE_FILE | \
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LANDLOCK_ACCESS_FS_READ_FILE)
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/* clang-format on */
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static int populate_ruleset(const char *const env_var, const int ruleset_fd,
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const __u64 allowed_access)
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{
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int num_paths, i, ret = 1;
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char *env_path_name;
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const char **path_list = NULL;
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struct landlock_path_beneath_attr path_beneath = {
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.parent_fd = -1,
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};
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env_path_name = getenv(env_var);
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if (!env_path_name) {
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/* Prevents users to forget a setting. */
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fprintf(stderr, "Missing environment variable %s\n", env_var);
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return 1;
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}
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env_path_name = strdup(env_path_name);
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unsetenv(env_var);
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num_paths = parse_path(env_path_name, &path_list);
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if (num_paths == 1 && path_list[0][0] == '\0') {
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/*
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* Allows to not use all possible restrictions (e.g. use
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* LL_FS_RO without LL_FS_RW).
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*/
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ret = 0;
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goto out_free_name;
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}
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for (i = 0; i < num_paths; i++) {
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struct stat statbuf;
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path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
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if (path_beneath.parent_fd < 0) {
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fprintf(stderr, "Failed to open \"%s\": %s\n",
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path_list[i], strerror(errno));
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goto out_free_name;
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}
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if (fstat(path_beneath.parent_fd, &statbuf)) {
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close(path_beneath.parent_fd);
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goto out_free_name;
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}
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path_beneath.allowed_access = allowed_access;
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if (!S_ISDIR(statbuf.st_mode))
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path_beneath.allowed_access &= ACCESS_FILE;
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if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
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&path_beneath, 0)) {
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fprintf(stderr,
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"Failed to update the ruleset with \"%s\": %s\n",
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path_list[i], strerror(errno));
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close(path_beneath.parent_fd);
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goto out_free_name;
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}
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close(path_beneath.parent_fd);
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}
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ret = 0;
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out_free_name:
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free(path_list);
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free(env_path_name);
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return ret;
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}
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/* clang-format off */
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#define ACCESS_FS_ROUGHLY_READ ( \
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LANDLOCK_ACCESS_FS_EXECUTE | \
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LANDLOCK_ACCESS_FS_READ_FILE | \
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LANDLOCK_ACCESS_FS_READ_DIR)
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#define ACCESS_FS_ROUGHLY_WRITE ( \
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LANDLOCK_ACCESS_FS_WRITE_FILE | \
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LANDLOCK_ACCESS_FS_REMOVE_DIR | \
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LANDLOCK_ACCESS_FS_REMOVE_FILE | \
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LANDLOCK_ACCESS_FS_MAKE_CHAR | \
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LANDLOCK_ACCESS_FS_MAKE_DIR | \
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LANDLOCK_ACCESS_FS_MAKE_REG | \
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LANDLOCK_ACCESS_FS_MAKE_SOCK | \
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LANDLOCK_ACCESS_FS_MAKE_FIFO | \
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LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
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LANDLOCK_ACCESS_FS_MAKE_SYM)
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/* clang-format on */
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int main(const int argc, char *const argv[], char *const *const envp)
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{
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const char *cmd_path;
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char *const *cmd_argv;
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int ruleset_fd;
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struct landlock_ruleset_attr ruleset_attr = {
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.handled_access_fs = ACCESS_FS_ROUGHLY_READ |
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ACCESS_FS_ROUGHLY_WRITE,
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};
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if (argc < 2) {
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fprintf(stderr,
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"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
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fprintf(stderr,
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"Launch a command in a restricted environment.\n\n");
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fprintf(stderr, "Environment variables containing paths, "
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"each separated by a colon:\n");
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fprintf(stderr,
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"* %s: list of paths allowed to be used in a read-only way.\n",
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ENV_FS_RO_NAME);
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fprintf(stderr,
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"* %s: list of paths allowed to be used in a read-write way.\n",
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ENV_FS_RW_NAME);
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fprintf(stderr,
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"\nexample:\n"
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"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
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"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
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"%s bash -i\n",
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
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return 1;
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}
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ruleset_fd =
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landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
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if (ruleset_fd < 0) {
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const int err = errno;
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perror("Failed to create a ruleset");
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switch (err) {
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case ENOSYS:
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fprintf(stderr,
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"Hint: Landlock is not supported by the current kernel. "
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"To support it, build the kernel with "
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"CONFIG_SECURITY_LANDLOCK=y and prepend "
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"\"landlock,\" to the content of CONFIG_LSM.\n");
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break;
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case EOPNOTSUPP:
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fprintf(stderr,
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"Hint: Landlock is currently disabled. "
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"It can be enabled in the kernel configuration by "
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"prepending \"landlock,\" to the content of CONFIG_LSM, "
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"or at boot time by setting the same content to the "
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"\"lsm\" kernel parameter.\n");
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break;
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}
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return 1;
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}
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if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
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ACCESS_FS_ROUGHLY_READ)) {
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goto err_close_ruleset;
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}
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if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd,
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ACCESS_FS_ROUGHLY_READ |
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ACCESS_FS_ROUGHLY_WRITE)) {
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goto err_close_ruleset;
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}
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if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
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perror("Failed to restrict privileges");
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goto err_close_ruleset;
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}
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if (landlock_restrict_self(ruleset_fd, 0)) {
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perror("Failed to enforce ruleset");
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goto err_close_ruleset;
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}
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close(ruleset_fd);
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cmd_path = argv[1];
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cmd_argv = argv + 1;
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execvpe(cmd_path, cmd_argv, envp);
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fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
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strerror(errno));
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fprintf(stderr, "Hint: access to the binary, the interpreter or "
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"shared libraries may be denied.\n");
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return 1;
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err_close_ruleset:
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close(ruleset_fd);
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return 1;
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}
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