samples/landlock: Support TCP restrictions

Add TCP restrictions to the sandboxer demo. It's possible to allow a
sandboxer to bind/connect to a list of specified ports restricting
network actions to the rest of them. This is controlled with the new
LL_TCP_BIND and LL_TCP_CONNECT environment variables.

Rename ENV_PATH_TOKEN to ENV_DELIMITER.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20231026014751.414649-12-konstantin.meskhidze@huawei.com
[mic: Extend commit message]
Signed-off-by: Mickaël Salaün <mic@digikod.net>

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index e2056c8b902c55408816d6db69b9d29dfe86d542..08596c0ef0707c3cb478a4c3c24540020c9848f6 100644 (file)
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -8,6 +8,8 @@
  */
 
 #define _GNU_SOURCE
+#define __SANE_USERSPACE_TYPES__
+#include <arpa/inet.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/landlock.h>
@@ -51,7 +53,9 @@ static inline int landlock_restrict_self(const int ruleset_fd,
 
 #define ENV_FS_RO_NAME "LL_FS_RO"
 #define ENV_FS_RW_NAME "LL_FS_RW"
-#define ENV_PATH_TOKEN ":"
+#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
+#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
+#define ENV_DELIMITER ":"
 
 static int parse_path(char *env_path, const char ***const path_list)
 {
@@ -60,13 +64,13 @@ static int parse_path(char *env_path, const char ***const path_list)
        if (env_path) {
                num_paths++;
                for (i = 0; env_path[i]; i++) {
-                       if (env_path[i] == ENV_PATH_TOKEN[0])
+                       if (env_path[i] == ENV_DELIMITER[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);
+               (*path_list)[i] = strsep(&env_path, ENV_DELIMITER);
 
        return num_paths;
 }
@@ -81,8 +85,8 @@ static int parse_path(char *env_path, const char ***const path_list)
 
 /* clang-format on */
 
-static int populate_ruleset(const char *const env_var, const int ruleset_fd,
-                           const __u64 allowed_access)
+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;
@@ -143,6 +147,39 @@ out_free_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, *strport;
+       struct landlock_net_port_attr net_port = {
+               .allowed_access = allowed_access,
+               .port = 0,
+       };
+
+       env_port_name = getenv(env_var);
+       if (!env_port_name)
+               return 0;
+       env_port_name = strdup(env_port_name);
+       unsetenv(env_var);
+
+       while ((strport = strsep(&env_port_name, ENV_DELIMITER))) {
+               net_port.port = atoi(strport);
+               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;
+}
+
 /* clang-format off */
 
 #define ACCESS_FS_ROUGHLY_READ ( \
@@ -166,39 +203,58 @@ out_free_name:
 
 /* clang-format on */
 
-#define LANDLOCK_ABI_LAST 3
+#define LANDLOCK_ABI_LAST 4
 
 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;
        __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,
        };
 
        if (argc < 2) {
                fprintf(stderr,
-                       "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
-                       ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+                       "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
+                       "<cmd> [args]...\n\n",
+                       ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
+                       ENV_TCP_CONNECT_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,
+                       "Environment variables containing paths and ports "
+                       "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",
+                       "* %s: list of paths allowed to be used in a read-write way.\n\n",
                        ENV_FS_RW_NAME);
+               fprintf(stderr,
+                       "Environment variables containing ports are optional "
+                       "and could be skipped.\n");
+               fprintf(stderr,
+                       "* %s: list of ports allowed to bind (server).\n",
+                       ENV_TCP_BIND_NAME);
+               fprintf(stderr,
+                       "* %s: list of ports allowed to connect (client).\n",
+                       ENV_TCP_CONNECT_NAME);
                fprintf(stderr,
                        "\nexample:\n"
                        "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
                        "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
+                       "%s=\"9418\" "
+                       "%s=\"80:443\" "
                        "%s bash -i\n\n",
-                       ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+                       ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
+                       ENV_TCP_CONNECT_NAME, argv[0]);
                fprintf(stderr,
                        "This sandboxer can use Landlock features "
                        "up to ABI version %d.\n",
@@ -255,7 +311,12 @@ int main(const int argc, char *const argv[], char *const *const envp)
        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);
                fprintf(stderr,
                        "Hint: You should update the running kernel "
                        "to leverage Landlock features "
@@ -274,18 +335,42 @@ int main(const int argc, char *const argv[], char *const *const envp)
        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;
+       }
+
        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(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
+
+       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(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
+
+       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;