snac2/landloc.h

/**
 *  Zero-Clause BSD
 *  ===============
 *
 *  Copyright 2024 shtrophic <christoph@liebender.dev>
 *
 *  Permission to use, copy, modify, and/or distribute this software for
 *  any purpose with or without fee is hereby granted.
 *
 *  THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL
 *  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE
 *  FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY
 *  DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 *  AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
 *  OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

/**
 * Repository: https://git.sr.ht/~shtrophic/landloc.h
 */

/**
 * Usage:
 *
 * Define a sandboxing function using the LL_BEGIN(...) and LL_END macros.
 * the arguments of LL_BEGIN are the function's signature.
 * Between those macros, implement your sandbox using LL_PATH() and LL_PORT() macros.
 * Calling LL_PATH() and LL_PORT() anywhere else will not work.
 * You may prepend `static` before LL_BEGIN to make the function static.
 * You need (should) wrap your sandboxing code in another set of braces:
 *
LL_BEGIN(my_sandbox_function, const char *rw_path) {

    LL_PATH(rw_path, LANDLOCK_ACCESS_FS_READ_FILE | LANDLOCK_ACCESS_FS_READ_DIR | LANDLOCK_ACCESS_FS_EXECUTE);
    LL_PORT(443, LANDLOCK_ACCESS_NET_CONNECT_TCP);

} LL_END

 *
 * Then, call it in your application's code.
 *

int main(void) {

    int status = my_sandbox_function("some/path");

    if (status != 0) {
        // error
    }

}

 *
 * You may define LL_PRINTERR(fmt, ...) before including this header to enable debug output:
 *

#define LL_PRINTERR(fmt, ...) fprintf(stderr, fmt "\n", __VA_ARGS__)
#include "landloc.h"

 */

#ifndef __LANDLOC_H__
#define __LANDLOC_H__

#ifndef __linux__
#   error "no landlock without linux"
#endif

#include <linux/version.h>

#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 13, 0)
#   error "no landlock on kernels older than 5.13.0"
#endif

#include <unistd.h>
#include <linux/landlock.h>
#include <sys/syscall.h>
#include <sys/prctl.h>
#include <fcntl.h>

#ifndef O_PATH
#   define O_PATH		010000000
#endif

#ifndef LL_PRINTERR
#   define LL_PRINTERR(fmt, ...) (void)fmt;
#else
#   include <string.h>
#   include <errno.h>
#endif

#ifdef LANDLOCK_ACCESS_FS_REFER
#   define LANDLOCK_ACCESS_FS_REFER_COMPAT LANDLOCK_ACCESS_FS_REFER
#   define __LL_SWITCH_FS_REFER __rattr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER_COMPAT
#else
#   define LANDLOCK_ACCESS_FS_REFER_COMPAT 0
#   define __LL_SWITCH_FS_REFER (void)0
#endif

#ifdef LANDLOCK_ACCESS_FS_TRUNCATE
#   define LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT LANDLOCK_ACCESS_FS_TRUNCATE
#   define __LL_SWITCH_FS_TRUNCATE __rattr.handled_access_fs  &= ~LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT
#else
#   define LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT 0
#   define __LL_SWITCH_FS_TRUNCATE (void)0
#endif

#ifdef LANDLOCK_ACCESS_FS_IOCTL_DEV
#   define LANDLOCK_ACCESS_FS_IOCTL_DEV_COMPAT LANDLOCK_ACCESS_FS_IOCTL_DEV
#   define __LL_SWITCH_FS_IOCTL_DEV __rattr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV_COMPAT
#else
#   define LANDLOCK_ACCESS_FS_IOCTL_DEV_COMPAT 0
#   define __LL_SWITCH_FS_IOCTL_DEV (void)0
#endif

#define LL_FS_ALL                           (\
    LANDLOCK_ACCESS_FS_EXECUTE              |\
    LANDLOCK_ACCESS_FS_WRITE_FILE           |\
    LANDLOCK_ACCESS_FS_READ_FILE            |\
    LANDLOCK_ACCESS_FS_READ_DIR             |\
    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_COMPAT         |\
    LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT      |\
    LANDLOCK_ACCESS_FS_IOCTL_DEV_COMPAT     )

#if defined(LANDLOCK_ACCESS_NET_BIND_TCP) && defined(LANDLOCK_ACCESS_NET_CONNECT_TCP)
#   define LL_HAVE_NET 1

#   define LANDLOCK_ACCESS_NET_BIND_TCP_COMPAT LANDLOCK_ACCESS_NET_BIND_TCP
#   define LANDLOCK_ACCESS_NET_CONNECT_TCP_COMPAT LANDLOCK_ACCESS_NET_CONNECT_TCP

#   define LL_NET_ALL (LANDLOCK_ACCESS_NET_BIND_TCP_COMPAT | LANDLOCK_ACCESS_NET_CONNECT_TCP_COMPAT)
#   define __LL_DECLARE_NET struct landlock_net_port_attr __nattr = {0}
#   define __LL_INIT_NET __rattr.handled_access_net = LL_NET_ALL
#   define __LL_SWITCH_NET do { __rattr.handled_access_net &= ~(LANDLOCK_ACCESS_NET_BIND_TCP | LANDLOCK_ACCESS_NET_CONNECT_TCP); } while (0)
#else
#   define LL_HAVE_NET 0

#   define LANDLOCK_ACCESS_NET_BIND_TCP_COMPAT 0
#   define LANDLOCK_ACCESS_NET_CONNECT_TCP_COMPAT 0

#   define LL_NET_ALL 0
#   define __LL_DECLARE_NET (void)0
#   define __LL_INIT_NET (void)0
#   define __LL_SWITCH_NET (void)0
#endif

#define LL_BEGIN(function, ...) int function(__VA_ARGS__) {\
    int ll_rule_fd, ll_abi;\
    struct landlock_ruleset_attr      __rattr = {0};\
    struct landlock_path_beneath_attr __pattr = {0};\
    __LL_DECLARE_NET;\
    int __err = 0;\
    __rattr.handled_access_fs  = LL_FS_ALL;\
    __LL_INIT_NET;\
    ll_abi = (int)syscall(SYS_landlock_create_ruleset, NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);\
    switch (ll_abi) {\
    case -1: return -1;\
    case  1: __LL_SWITCH_FS_REFER; __attribute__((fallthrough));\
    case  2: __LL_SWITCH_FS_TRUNCATE; __attribute__((fallthrough));\
    case  3: __LL_SWITCH_NET; __attribute__((fallthrough));\
    case  4: __LL_SWITCH_FS_IOCTL_DEV;\
    default: break;\
    }\
    ll_rule_fd = (int)syscall(SYS_landlock_create_ruleset, &__rattr, sizeof(struct landlock_ruleset_attr), 0);\
    if (-1 == ll_rule_fd) {\
        LL_PRINTERR("landlock_create_ruleset: %s", strerror(errno));\
        return -1;\
    }

#define LL_END \
    __err = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);\
    if (-1 == __err) {\
        LL_PRINTERR("set_no_new_privs: %s", strerror(errno));\
        goto __close;\
    }\
    __err = (int)syscall(SYS_landlock_restrict_self, ll_rule_fd, 0);\
    if (__err)\
        LL_PRINTERR("landlock_restrict_self: %s", strerror(errno));\
    __close: close(ll_rule_fd);\
    return __err; }

#define LL_PATH(p, rules) do {\
    const char *__path = (p);\
    __pattr.allowed_access = (rules) & __rattr.handled_access_fs;\
    if (__pattr.allowed_access != 0) {\
        __pattr.parent_fd = open(__path, O_PATH | O_CLOEXEC);\
        if (-1 == __pattr.parent_fd) {\
            LL_PRINTERR("open(%s): %s", __path, strerror(errno));\
            __err = -1;\
            goto __close;\
        }\
        __err = (int)syscall(SYS_landlock_add_rule, ll_rule_fd, LANDLOCK_RULE_PATH_BENEATH, &__pattr, 0);\
        if (__err) {\
            LL_PRINTERR("landlock_add_rule(%s): %s", __path, strerror(errno));\
            goto __close;\
        }\
        close(__pattr.parent_fd);\
    }\
} while (0)

#if LL_HAVE_NET

#define LL_PORT(p, rules) do {\
    unsigned short __port = (p);\
    __nattr.allowed_access = (rules);\
    if (ll_abi > 3 && __nattr.allowed_access != 0) {\
        __nattr.port = __port;\
        __err = (int)syscall(SYS_landlock_add_rule, ll_rule_fd, LANDLOCK_RULE_NET_PORT, &__nattr, 0);\
        if (__err) {\
            LL_PRINTERR("landlock_add_rule(%u): %s", __port, strerror(errno));\
            goto __close;\
        }\
    }\
} while (0)

#else

#define LL_PORT(p, rules) do {\
    unsigned short __port = (p);\
    __u64 __rules = (rules);\
    (void)__port;\
    (void)__rules;\
} while (0)

#endif /* LL_HAVE_NET */

#endif /* __LANDLOC_H__ */