diff options
Diffstat (limited to 'samples/landlock/sandboxer.c')
| -rw-r--r-- | samples/landlock/sandboxer.c | 539 |
1 files changed, 539 insertions, 0 deletions
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c new file mode 100644 index 000000000000..e7af02f98208 --- /dev/null +++ b/samples/landlock/sandboxer.c @@ -0,0 +1,539 @@ +// SPDX-License-Identifier: BSD-3-Clause +/* + * Simple Landlock sandbox manager able to execute a process restricted by + * user-defined file system and network access control policies. + * + * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2020 ANSSI + */ + +#define _GNU_SOURCE +#define __SANE_USERSPACE_TYPES__ +#include <arpa/inet.h> +#include <errno.h> +#include <fcntl.h> +#include <linux/landlock.h> +#include <linux/socket.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> +#include <stdbool.h> + +#if defined(__GLIBC__) +#include <linux/prctl.h> +#endif + +#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_TCP_BIND_NAME "LL_TCP_BIND" +#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" +#define ENV_SCOPED_NAME "LL_SCOPED" +#define ENV_FORCE_LOG_NAME "LL_FORCE_LOG" +#define ENV_DELIMITER ":" + +static int str2num(const char *numstr, __u64 *num_dst) +{ + char *endptr = NULL; + int err = 0; + __u64 num; + + errno = 0; + num = strtoull(numstr, &endptr, 10); + if (errno != 0) + err = errno; + /* Was the string empty, or not entirely parsed successfully? */ + else if ((*numstr == '\0') || (*endptr != '\0')) + err = EINVAL; + else + *num_dst = num; + + return err; +} + +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_DELIMITER[0]) + num_paths++; + } + } + *path_list = malloc(num_paths * sizeof(**path_list)); + if (!*path_list) + return -1; + + for (i = 0; i < num_paths; i++) + (*path_list)[i] = strsep(&env_path, ENV_DELIMITER); + + return num_paths; +} + +/* clang-format off */ + +#define ACCESS_FILE ( \ + LANDLOCK_ACCESS_FS_EXECUTE | \ + LANDLOCK_ACCESS_FS_WRITE_FILE | \ + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_TRUNCATE | \ + LANDLOCK_ACCESS_FS_IOCTL_DEV) + +/* clang-format on */ + +static int populate_ruleset_fs(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 < 0) { + fprintf(stderr, "Failed to allocate memory\n"); + goto out_free_name; + } + 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)); + continue; + } + if (fstat(path_beneath.parent_fd, &statbuf)) { + fprintf(stderr, "Failed to stat \"%s\": %s\n", + path_list[i], strerror(errno)); + 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(path_list); + free(env_path_name); + return ret; +} + +static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, + const __u64 allowed_access) +{ + int ret = 1; + char *env_port_name, *env_port_name_next, *strport; + struct landlock_net_port_attr net_port = { + .allowed_access = allowed_access, + }; + + env_port_name = getenv(env_var); + if (!env_port_name) + return 0; + env_port_name = strdup(env_port_name); + unsetenv(env_var); + + env_port_name_next = env_port_name; + while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) { + __u64 port; + + if (strcmp(strport, "") == 0) + continue; + + if (str2num(strport, &port)) { + fprintf(stderr, "Failed to parse port at \"%s\"\n", + strport); + goto out_free_name; + } + net_port.port = port; + if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT, + &net_port, 0)) { + fprintf(stderr, + "Failed to update the ruleset with port \"%llu\": %s\n", + net_port.port, strerror(errno)); + goto out_free_name; + } + } + ret = 0; + +out_free_name: + free(env_port_name); + return ret; +} + +/* Returns true on error, false otherwise. */ +static bool check_ruleset_scope(const char *const env_var, + struct landlock_ruleset_attr *ruleset_attr) +{ + char *env_type_scope, *env_type_scope_next, *ipc_scoping_name; + bool error = false; + bool abstract_scoping = false; + bool signal_scoping = false; + + /* Scoping is not supported by Landlock ABI */ + if (!(ruleset_attr->scoped & + (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL))) + goto out_unset; + + env_type_scope = getenv(env_var); + /* Scoping is not supported by the user */ + if (!env_type_scope || strcmp("", env_type_scope) == 0) + goto out_unset; + + env_type_scope = strdup(env_type_scope); + env_type_scope_next = env_type_scope; + while ((ipc_scoping_name = + strsep(&env_type_scope_next, ENV_DELIMITER))) { + if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) { + abstract_scoping = true; + } else if (strcmp("s", ipc_scoping_name) == 0 && + !signal_scoping) { + signal_scoping = true; + } else { + fprintf(stderr, "Unknown or duplicate scope \"%s\"\n", + ipc_scoping_name); + error = true; + goto out_free_name; + } + } + +out_free_name: + free(env_type_scope); + +out_unset: + if (!abstract_scoping) + ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET; + if (!signal_scoping) + ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL; + + unsetenv(env_var); + return error; +} + +/* clang-format off */ + +#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 | \ + LANDLOCK_ACCESS_FS_REFER | \ + LANDLOCK_ACCESS_FS_TRUNCATE | \ + LANDLOCK_ACCESS_FS_IOCTL_DEV) + +/* clang-format on */ + +#define LANDLOCK_ABI_LAST 7 + +#define XSTR(s) #s +#define STR(s) XSTR(s) + +/* clang-format off */ + +static const char help[] = + "usage: " ENV_FS_RO_NAME "=\"...\" " ENV_FS_RW_NAME "=\"...\" " + "[other environment variables] %1$s <cmd> [args]...\n" + "\n" + "Execute the given command in a restricted environment.\n" + "Multi-valued settings (lists of ports, paths, scopes) are colon-delimited.\n" + "\n" + "Mandatory settings:\n" + "* " ENV_FS_RO_NAME ": paths allowed to be used in a read-only way\n" + "* " ENV_FS_RW_NAME ": paths allowed to be used in a read-write way\n" + "\n" + "Optional settings (when not set, their associated access check " + "is always allowed, which is different from an empty string which " + "means an empty list):\n" + "* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n" + "* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n" + "* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n" + " - \"a\" to restrict opening abstract unix sockets\n" + " - \"s\" to restrict sending signals\n" + "\n" + "A sandboxer should not log denied access requests to avoid spamming logs, " + "but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n" + "\n" + "Example:\n" + ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " + ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " + ENV_TCP_BIND_NAME "=\"9418\" " + ENV_TCP_CONNECT_NAME "=\"80:443\" " + ENV_SCOPED_NAME "=\"a:s\" " + "%1$s bash -i\n" + "\n" + "This sandboxer can use Landlock features up to ABI version " + STR(LANDLOCK_ABI_LAST) ".\n"; + +/* clang-format on */ + +int main(const int argc, char *const argv[], char *const *const envp) +{ + const char *cmd_path; + char *const *cmd_argv; + int ruleset_fd, abi; + char *env_port_name, *env_force_log; + __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ, + access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE; + + struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = access_fs_rw, + .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | + LANDLOCK_ACCESS_NET_CONNECT_TCP, + .scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | + LANDLOCK_SCOPE_SIGNAL, + }; + int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; + int set_restrict_flags = 0; + + if (argc < 2) { + fprintf(stderr, help, argv[0]); + return 1; + } + + abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); + if (abi < 0) { + const int err = errno; + + perror("Failed to check Landlock compatibility"); + 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; + } + + /* Best-effort security. */ + switch (abi) { + case 1: + /* + * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 + * + * Note: The "refer" operations (file renaming and linking + * across different directories) are always forbidden when using + * Landlock with ABI 1. + * + * If only ABI 1 is available, this sandboxer knowingly forbids + * refer operations. + * + * If a program *needs* to do refer operations after enabling + * Landlock, it can not use Landlock at ABI level 1. To be + * compatible with different kernel versions, such programs + * should then fall back to not restrict themselves at all if + * the running kernel only supports ABI 1. + */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; + __attribute__((fallthrough)); + case 2: + /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; + __attribute__((fallthrough)); + case 3: + /* Removes network support for ABI < 4 */ + ruleset_attr.handled_access_net &= + ~(LANDLOCK_ACCESS_NET_BIND_TCP | + LANDLOCK_ACCESS_NET_CONNECT_TCP); + __attribute__((fallthrough)); + case 4: + /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; + + __attribute__((fallthrough)); + case 5: + /* Removes LANDLOCK_SCOPE_* for ABI < 6 */ + ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | + LANDLOCK_SCOPE_SIGNAL); + __attribute__((fallthrough)); + case 6: + /* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */ + supported_restrict_flags &= + ~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; + + /* Must be printed for any ABI < LANDLOCK_ABI_LAST. */ + fprintf(stderr, + "Hint: You should update the running kernel " + "to leverage Landlock features " + "provided by ABI version %d (instead of %d).\n", + LANDLOCK_ABI_LAST, abi); + __attribute__((fallthrough)); + case LANDLOCK_ABI_LAST: + break; + default: + fprintf(stderr, + "Hint: You should update this sandboxer " + "to leverage Landlock features " + "provided by ABI version %d (instead of %d).\n", + abi, LANDLOCK_ABI_LAST); + } + access_fs_ro &= ruleset_attr.handled_access_fs; + access_fs_rw &= ruleset_attr.handled_access_fs; + + /* Removes bind access attribute if not supported by a user. */ + env_port_name = getenv(ENV_TCP_BIND_NAME); + if (!env_port_name) { + ruleset_attr.handled_access_net &= + ~LANDLOCK_ACCESS_NET_BIND_TCP; + } + /* Removes connect access attribute if not supported by a user. */ + env_port_name = getenv(ENV_TCP_CONNECT_NAME); + if (!env_port_name) { + ruleset_attr.handled_access_net &= + ~LANDLOCK_ACCESS_NET_CONNECT_TCP; + } + + if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr)) + return 1; + + /* Enables optional logs. */ + env_force_log = getenv(ENV_FORCE_LOG_NAME); + if (env_force_log) { + if (strcmp(env_force_log, "1") != 0) { + fprintf(stderr, "Unknown value for " ENV_FORCE_LOG_NAME + " (only \"1\" is handled)\n"); + return 1; + } + if (!(supported_restrict_flags & + LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON)) { + fprintf(stderr, + "Audit logs not supported by current kernel\n"); + return 1; + } + set_restrict_flags |= LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; + unsetenv(ENV_FORCE_LOG_NAME); + } + + ruleset_fd = + landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); + if (ruleset_fd < 0) { + perror("Failed to create a ruleset"); + return 1; + } + + if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) { + goto err_close_ruleset; + } + if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) { + goto err_close_ruleset; + } + + if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd, + LANDLOCK_ACCESS_NET_BIND_TCP)) { + goto err_close_ruleset; + } + if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd, + LANDLOCK_ACCESS_NET_CONNECT_TCP)) { + 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, set_restrict_flags)) { + perror("Failed to enforce ruleset"); + goto err_close_ruleset; + } + close(ruleset_fd); + + cmd_path = argv[1]; + cmd_argv = argv + 1; + fprintf(stderr, "Executing the sandboxed command...\n"); + 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; +} |