diff options
Diffstat (limited to 'samples/landlock/sandboxer.c')
| -rw-r--r-- | samples/landlock/sandboxer.c | 238 |
1 files changed, 238 insertions, 0 deletions
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c new file mode 100644 index 000000000000..7a15910d2171 --- /dev/null +++ b/samples/landlock/sandboxer.c @@ -0,0 +1,238 @@ +// SPDX-License-Identifier: BSD-3-Clause +/* + * Simple Landlock sandbox manager able to launch a process restricted by a + * user-defined filesystem access control policy. + * + * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2020 ANSSI + */ + +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <linux/landlock.h> +#include <linux/prctl.h> +#include <stddef.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/prctl.h> +#include <sys/stat.h> +#include <sys/syscall.h> +#include <unistd.h> + +#ifndef landlock_create_ruleset +static inline int landlock_create_ruleset( + const struct landlock_ruleset_attr *const attr, + const size_t size, const __u32 flags) +{ + return syscall(__NR_landlock_create_ruleset, attr, size, flags); +} +#endif + +#ifndef landlock_add_rule +static inline int landlock_add_rule(const int ruleset_fd, + const enum landlock_rule_type rule_type, + const void *const rule_attr, const __u32 flags) +{ + return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, + rule_attr, flags); +} +#endif + +#ifndef landlock_restrict_self +static inline int landlock_restrict_self(const int ruleset_fd, + const __u32 flags) +{ + return syscall(__NR_landlock_restrict_self, ruleset_fd, flags); +} +#endif + +#define ENV_FS_RO_NAME "LL_FS_RO" +#define ENV_FS_RW_NAME "LL_FS_RW" +#define ENV_PATH_TOKEN ":" + +static int parse_path(char *env_path, const char ***const path_list) +{ + int i, num_paths = 0; + + if (env_path) { + num_paths++; + for (i = 0; env_path[i]; i++) { + if (env_path[i] == ENV_PATH_TOKEN[0]) + num_paths++; + } + } + *path_list = malloc(num_paths * sizeof(**path_list)); + for (i = 0; i < num_paths; i++) + (*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN); + + return num_paths; +} + +#define ACCESS_FILE ( \ + LANDLOCK_ACCESS_FS_EXECUTE | \ + LANDLOCK_ACCESS_FS_WRITE_FILE | \ + LANDLOCK_ACCESS_FS_READ_FILE) + +static int populate_ruleset( + const char *const env_var, const int ruleset_fd, + const __u64 allowed_access) +{ + int num_paths, i, ret = 1; + char *env_path_name; + const char **path_list = NULL; + struct landlock_path_beneath_attr path_beneath = { + .parent_fd = -1, + }; + + env_path_name = getenv(env_var); + if (!env_path_name) { + /* Prevents users to forget a setting. */ + fprintf(stderr, "Missing environment variable %s\n", env_var); + return 1; + } + env_path_name = strdup(env_path_name); + unsetenv(env_var); + num_paths = parse_path(env_path_name, &path_list); + if (num_paths == 1 && path_list[0][0] == '\0') { + /* + * Allows to not use all possible restrictions (e.g. use + * LL_FS_RO without LL_FS_RW). + */ + ret = 0; + goto out_free_name; + } + + for (i = 0; i < num_paths; i++) { + struct stat statbuf; + + path_beneath.parent_fd = open(path_list[i], O_PATH | + O_CLOEXEC); + if (path_beneath.parent_fd < 0) { + fprintf(stderr, "Failed to open \"%s\": %s\n", + path_list[i], + strerror(errno)); + goto out_free_name; + } + if (fstat(path_beneath.parent_fd, &statbuf)) { + close(path_beneath.parent_fd); + goto out_free_name; + } + path_beneath.allowed_access = allowed_access; + if (!S_ISDIR(statbuf.st_mode)) + path_beneath.allowed_access &= ACCESS_FILE; + if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, + &path_beneath, 0)) { + fprintf(stderr, "Failed to update the ruleset with \"%s\": %s\n", + path_list[i], strerror(errno)); + close(path_beneath.parent_fd); + goto out_free_name; + } + close(path_beneath.parent_fd); + } + ret = 0; + +out_free_name: + free(env_path_name); + return ret; +} + +#define ACCESS_FS_ROUGHLY_READ ( \ + LANDLOCK_ACCESS_FS_EXECUTE | \ + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_READ_DIR) + +#define ACCESS_FS_ROUGHLY_WRITE ( \ + LANDLOCK_ACCESS_FS_WRITE_FILE | \ + LANDLOCK_ACCESS_FS_REMOVE_DIR | \ + LANDLOCK_ACCESS_FS_REMOVE_FILE | \ + LANDLOCK_ACCESS_FS_MAKE_CHAR | \ + LANDLOCK_ACCESS_FS_MAKE_DIR | \ + LANDLOCK_ACCESS_FS_MAKE_REG | \ + LANDLOCK_ACCESS_FS_MAKE_SOCK | \ + LANDLOCK_ACCESS_FS_MAKE_FIFO | \ + LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ + LANDLOCK_ACCESS_FS_MAKE_SYM) + +int main(const int argc, char *const argv[], char *const *const envp) +{ + const char *cmd_path; + char *const *cmd_argv; + int ruleset_fd; + struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = ACCESS_FS_ROUGHLY_READ | + ACCESS_FS_ROUGHLY_WRITE, + }; + + if (argc < 2) { + fprintf(stderr, "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n", + ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]); + fprintf(stderr, "Launch a command in a restricted environment.\n\n"); + fprintf(stderr, "Environment variables containing paths, " + "each separated by a colon:\n"); + fprintf(stderr, "* %s: list of paths allowed to be used in a read-only way.\n", + ENV_FS_RO_NAME); + fprintf(stderr, "* %s: list of paths allowed to be used in a read-write way.\n", + ENV_FS_RW_NAME); + fprintf(stderr, "\nexample:\n" + "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" " + "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " + "%s bash -i\n", + ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]); + return 1; + } + + ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); + if (ruleset_fd < 0) { + const int err = errno; + + perror("Failed to create a ruleset"); + switch (err) { + case ENOSYS: + fprintf(stderr, "Hint: Landlock is not supported by the current kernel. " + "To support it, build the kernel with " + "CONFIG_SECURITY_LANDLOCK=y and prepend " + "\"landlock,\" to the content of CONFIG_LSM.\n"); + break; + case EOPNOTSUPP: + fprintf(stderr, "Hint: Landlock is currently disabled. " + "It can be enabled in the kernel configuration by " + "prepending \"landlock,\" to the content of CONFIG_LSM, " + "or at boot time by setting the same content to the " + "\"lsm\" kernel parameter.\n"); + break; + } + return 1; + } + if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, + ACCESS_FS_ROUGHLY_READ)) { + goto err_close_ruleset; + } + if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, + ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE)) { + goto err_close_ruleset; + } + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { + perror("Failed to restrict privileges"); + goto err_close_ruleset; + } + if (landlock_restrict_self(ruleset_fd, 0)) { + perror("Failed to enforce ruleset"); + goto err_close_ruleset; + } + close(ruleset_fd); + + cmd_path = argv[1]; + cmd_argv = argv + 1; + execvpe(cmd_path, cmd_argv, envp); + fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, + strerror(errno)); + fprintf(stderr, "Hint: access to the binary, the interpreter or " + "shared libraries may be denied.\n"); + return 1; + +err_close_ruleset: + close(ruleset_fd); + return 1; +} |