Merge pull request 'Port sandboxing to linux via landlock' (#226) from shtrophic/snac2:master into master

Reviewed-on: https://codeberg.org/grunfink/snac2/pulls/226

5 files changed, 358 insertions, 39 deletions

diff --git a/Makefile b/Makefile
index 05e65f5..2977cd4 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ CFLAGS?=-g -Wall -Wextra -pedantic
 
 all: snac
 
-snac: snac.o main.o data.o http.o httpd.o webfinger.o \
+snac: snac.o main.o sandbox.o data.o http.o httpd.o webfinger.o \
     activitypub.o html.o utils.o format.o upgrade.o mastoapi.o
         $(CC) $(CFLAGS) -L$(PREFIX)/lib *.o -lcurl -lcrypto $(LDFLAGS) -pthread -o $@
 
@@ -36,6 +36,9 @@ uninstall:
 activitypub.o: activitypub.c xs.h xs_json.h xs_curl.h xs_mime.h \
  xs_openssl.h xs_regex.h xs_time.h xs_set.h xs_match.h snac.h \
  http_codes.h
+sandbox.o: sandbox.c xs.h xs_hex.h xs_io.h xs_json.h xs_openssl.h \
+ xs_glob.h xs_set.h xs_time.h xs_regex.h xs_match.h xs_unicode.h \
+ landloc.h snac.h
 data.o: data.c xs.h xs_hex.h xs_io.h xs_json.h xs_openssl.h xs_glob.h \
  xs_set.h xs_time.h xs_regex.h xs_match.h xs_unicode.h xs_random.h snac.h \
  http_codes.h
diff --git a/data.c b/data.c
index e5d7258..0fd3528 100644
--- a/data.c
+++ b/data.c
@@ -115,44 +115,7 @@ int srv_open(const char *basedir, int auto_upgrade)
 #define st_mtim st_mtimespec
 #endif
 
-#ifdef __OpenBSD__
-    if (xs_is_true(xs_dict_get(srv_config, "disable_openbsd_security"))) {
-        srv_debug(1, xs_dup("OpenBSD security disabled by admin"));
-    }
-    else {
-        int smail = !xs_is_true(xs_dict_get(srv_config, "disable_email_notifications"));
-        const char *address = xs_dict_get(srv_config, "address");
-
-        srv_debug(1, xs_fmt("Calling unveil()"));
-        unveil(basedir,                "rwc");
-        unveil("/tmp",                 "rwc");
-        unveil("/etc/resolv.conf",     "r");
-        unveil("/etc/hosts",           "r");
-        unveil("/etc/ssl/openssl.cnf", "r");
-        unveil("/etc/ssl/cert.pem",    "r");
-        unveil("/usr/share/zoneinfo",  "r");
-
-        if (smail)
-            unveil("/usr/sbin/sendmail",   "x");
-
-        if (*address == '/')
-            unveil(address, "rwc");
-
-        unveil(NULL,                   NULL);
-
-        srv_debug(1, xs_fmt("Calling pledge()"));
-
-        xs *p = xs_str_new("stdio rpath wpath cpath flock inet proc dns fattr");
-
-        if (smail)
-            p = xs_str_cat(p, " exec");
-
-        if (*address == '/')
-            p = xs_str_cat(p, " unix");
-
-        pledge(p, NULL);
-    }
-#endif /* __OpenBSD__ */
+    sbox_enter(srv_basedir);
 
     /* read (and drop) emojis.json, possibly creating it */
     xs_free(emojis());
diff --git a/landloc.h b/landloc.h
new file mode 100644
index 0000000..1e717c9
--- /dev/null
+++ b/landloc.h
@@ -0,0 +1,238 @@
+/**
+ *  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__ */
diff --git a/sandbox.c b/sandbox.c
new file mode 100644
index 0000000..f417e86
--- /dev/null
+++ b/sandbox.c
@@ -0,0 +1,113 @@
+#include "xs.h"
+
+#include "snac.h"
+
+#include <unistd.h>
+
+#if defined (__linux__)
+
+#define LL_PRINTERR(fmt, ...) srv_debug(0, xs_fmt(fmt, __VA_ARGS__))
+#include "landloc.h"
+
+static
+LL_BEGIN(sbox_enter_linux_, const char* basedir, const char *address, int smail) {
+
+    const unsigned long long
+        rd = LANDLOCK_ACCESS_FS_READ_DIR,
+        rf = LANDLOCK_ACCESS_FS_READ_FILE,
+        w  = LANDLOCK_ACCESS_FS_WRITE_FILE      |
+             LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT,
+        c  = LANDLOCK_ACCESS_FS_MAKE_DIR        |
+             LANDLOCK_ACCESS_FS_MAKE_REG        |
+             LANDLOCK_ACCESS_FS_TRUNCATE_COMPAT |
+             LANDLOCK_ACCESS_FS_MAKE_SYM        |
+             LANDLOCK_ACCESS_FS_REMOVE_DIR      |
+             LANDLOCK_ACCESS_FS_REMOVE_FILE     |
+             LANDLOCK_ACCESS_FS_REFER_COMPAT,
+        s  = LANDLOCK_ACCESS_FS_MAKE_SOCK,
+        x  = LANDLOCK_ACCESS_FS_EXECUTE;
+
+    LL_PATH(basedir,                rf|rd|w|c);
+    LL_PATH("/tmp",                 rf|rd|w|c);
+#ifndef WITHOUT_SHM
+    LL_PATH("/dev/shm",             rf|w|c   );
+#endif
+    LL_PATH("/etc/resolv.conf",     rf       );
+    LL_PATH("/etc/hosts",           rf       );
+    LL_PATH("/etc/ssl/openssl.cnf", rf       );
+    LL_PATH("/etc/ssl/cert.pem",    rf       );
+    LL_PATH("/usr/share/zoneinfo",  rf       );
+
+    if (*address == '/')
+        LL_PATH(address, s);
+
+    if (smail)
+        LL_PATH("/usr/sbin/sendmail", x);
+
+    if (*address != '/') {
+        unsigned short listen_port = xs_number_get(xs_dict_get(srv_config, "port"));
+        LL_PORT(listen_port, LANDLOCK_ACCESS_NET_BIND_TCP_COMPAT);
+    }
+
+    LL_PORT(80,  LANDLOCK_ACCESS_NET_CONNECT_TCP_COMPAT);
+    LL_PORT(443, LANDLOCK_ACCESS_NET_CONNECT_TCP_COMPAT);
+
+} LL_END
+
+#endif
+
+void sbox_enter(const char *basedir)
+{
+    if (xs_is_true(xs_dict_get(srv_config, "disable_openbsd_security"))) {
+        srv_log(xs_dup("disable_openbsd_security is deprecated. Use disable_sandbox instead."));
+        return;
+    }
+    if (xs_is_true(xs_dict_get(srv_config, "disable_sandbox"))) {
+        srv_debug(0, xs_dup("Sandbox disabled by admin"));
+        return;
+    }
+
+    const char *address = xs_dict_get(srv_config, "address");
+
+    int smail = !xs_is_true(xs_dict_get(srv_config, "disable_email_notifications"));
+
+#if defined (__OpenBSD__)
+    srv_debug(1, xs_fmt("Calling unveil()"));
+    unveil(basedir,                "rwc");
+    unveil("/tmp",                 "rwc");
+    unveil("/etc/resolv.conf",     "r");
+    unveil("/etc/hosts",           "r");
+    unveil("/etc/ssl/openssl.cnf", "r");
+    unveil("/etc/ssl/cert.pem",    "r");
+    unveil("/usr/share/zoneinfo",  "r");
+
+    if (smail)
+        unveil("/usr/sbin/sendmail",   "x");
+
+    if (*address == '/')
+        unveil(address, "rwc");
+
+    unveil(NULL,                   NULL);
+
+    srv_debug(1, xs_fmt("Calling pledge()"));
+
+    xs *p = xs_str_new("stdio rpath wpath cpath flock inet proc dns fattr");
+
+    if (smail)
+        p = xs_str_cat(p, " exec");
+
+    if (*address == '/')
+        p = xs_str_cat(p, " unix");
+
+    pledge(p, NULL);
+
+    xs_free(p);
+#elif defined (__linux__)
+    
+    if (sbox_enter_linux_(basedir, address, smail) == 0)
+        srv_log(xs_dup("landlocked"));
+    else
+        srv_log(xs_dup("landlocking failed"));
+
+#endif
+}
diff --git a/snac.h b/snac.h
index c9ba28b..ec3ee5c 100644
--- a/snac.h
+++ b/snac.h
@@ -75,6 +75,8 @@ void snac_log(snac *user, xs_str *str);
 int srv_open(const char *basedir, int auto_upgrade);
 void srv_free(void);
 
+void sbox_enter(const char *basedir);
+
 int user_open(snac *snac, const char *uid);
 void user_free(snac *snac);
 xs_list *user_list(void);