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>
This commit is contained in:
Konstantin Meskhidze
Mickaël Salaün
parent
a549d055a2
commit
5e990dcef1
@ -8,6 +8,8 @@
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*/
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#define _GNU_SOURCE
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#define __SANE_USERSPACE_TYPES__
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#include <arpa/inet.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/landlock.h>
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@ -51,7 +53,9 @@ static inline int landlock_restrict_self(const int ruleset_fd,
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#define ENV_FS_RO_NAME "LL_FS_RO"
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#define ENV_FS_RW_NAME "LL_FS_RW"
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#define ENV_PATH_TOKEN ":"
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#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
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#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
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#define ENV_DELIMITER ":"
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static int parse_path(char *env_path, const char ***const path_list)
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{
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@ -60,13 +64,13 @@ static int parse_path(char *env_path, const char ***const path_list)
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if (env_path) {
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num_paths++;
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for (i = 0; env_path[i]; i++) {
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if (env_path[i] == ENV_PATH_TOKEN[0])
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if (env_path[i] == ENV_DELIMITER[0])
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num_paths++;
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}
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}
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*path_list = malloc(num_paths * sizeof(**path_list));
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for (i = 0; i < num_paths; i++)
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(*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
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(*path_list)[i] = strsep(&env_path, ENV_DELIMITER);
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return num_paths;
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}
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@ -81,8 +85,8 @@ static int parse_path(char *env_path, const char ***const path_list)
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/* clang-format on */
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static int populate_ruleset(const char *const env_var, const int ruleset_fd,
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const __u64 allowed_access)
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static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
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const __u64 allowed_access)
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{
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int num_paths, i, ret = 1;
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char *env_path_name;
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@ -143,6 +147,39 @@ out_free_name:
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return ret;
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}
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static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
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const __u64 allowed_access)
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{
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int ret = 1;
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char *env_port_name, *strport;
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struct landlock_net_port_attr net_port = {
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.allowed_access = allowed_access,
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.port = 0,
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};
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env_port_name = getenv(env_var);
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if (!env_port_name)
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return 0;
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env_port_name = strdup(env_port_name);
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unsetenv(env_var);
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while ((strport = strsep(&env_port_name, ENV_DELIMITER))) {
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net_port.port = atoi(strport);
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if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
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&net_port, 0)) {
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fprintf(stderr,
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"Failed to update the ruleset with port \"%llu\": %s\n",
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net_port.port, strerror(errno));
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goto out_free_name;
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}
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}
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ret = 0;
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out_free_name:
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free(env_port_name);
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return ret;
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}
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/* clang-format off */
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#define ACCESS_FS_ROUGHLY_READ ( \
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@ -166,39 +203,58 @@ out_free_name:
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/* clang-format on */
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#define LANDLOCK_ABI_LAST 3
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#define LANDLOCK_ABI_LAST 4
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int main(const int argc, char *const argv[], char *const *const envp)
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{
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const char *cmd_path;
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char *const *cmd_argv;
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int ruleset_fd, abi;
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char *env_port_name;
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__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
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access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
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struct landlock_ruleset_attr ruleset_attr = {
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.handled_access_fs = access_fs_rw,
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.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
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LANDLOCK_ACCESS_NET_CONNECT_TCP,
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};
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if (argc < 2) {
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fprintf(stderr,
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"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
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"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
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"<cmd> [args]...\n\n",
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
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ENV_TCP_CONNECT_NAME, argv[0]);
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fprintf(stderr,
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"Launch a command in a restricted environment.\n\n");
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fprintf(stderr, "Environment variables containing paths, "
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"each separated by a colon:\n");
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fprintf(stderr,
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"Environment variables containing paths and ports "
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"each separated by a colon:\n");
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fprintf(stderr,
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"* %s: list of paths allowed to be used in a read-only way.\n",
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ENV_FS_RO_NAME);
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fprintf(stderr,
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"* %s: list of paths allowed to be used in a read-write way.\n",
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"* %s: list of paths allowed to be used in a read-write way.\n\n",
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ENV_FS_RW_NAME);
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fprintf(stderr,
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"Environment variables containing ports are optional "
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"and could be skipped.\n");
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fprintf(stderr,
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"* %s: list of ports allowed to bind (server).\n",
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ENV_TCP_BIND_NAME);
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fprintf(stderr,
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"* %s: list of ports allowed to connect (client).\n",
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ENV_TCP_CONNECT_NAME);
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fprintf(stderr,
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"\nexample:\n"
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"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
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"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
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"%s=\"9418\" "
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"%s=\"80:443\" "
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"%s bash -i\n\n",
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
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ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
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ENV_TCP_CONNECT_NAME, argv[0]);
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fprintf(stderr,
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"This sandboxer can use Landlock features "
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"up to ABI version %d.\n",
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@ -255,7 +311,12 @@ int main(const int argc, char *const argv[], char *const *const envp)
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case 2:
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/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
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ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
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__attribute__((fallthrough));
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case 3:
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/* Removes network support for ABI < 4 */
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ruleset_attr.handled_access_net &=
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~(LANDLOCK_ACCESS_NET_BIND_TCP |
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LANDLOCK_ACCESS_NET_CONNECT_TCP);
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fprintf(stderr,
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"Hint: You should update the running kernel "
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"to leverage Landlock features "
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@ -274,18 +335,42 @@ int main(const int argc, char *const argv[], char *const *const envp)
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access_fs_ro &= ruleset_attr.handled_access_fs;
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access_fs_rw &= ruleset_attr.handled_access_fs;
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/* Removes bind access attribute if not supported by a user. */
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env_port_name = getenv(ENV_TCP_BIND_NAME);
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if (!env_port_name) {
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ruleset_attr.handled_access_net &=
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~LANDLOCK_ACCESS_NET_BIND_TCP;
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}
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/* Removes connect access attribute if not supported by a user. */
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env_port_name = getenv(ENV_TCP_CONNECT_NAME);
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if (!env_port_name) {
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ruleset_attr.handled_access_net &=
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~LANDLOCK_ACCESS_NET_CONNECT_TCP;
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}
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ruleset_fd =
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landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
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if (ruleset_fd < 0) {
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perror("Failed to create a ruleset");
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return 1;
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}
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if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
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if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
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goto err_close_ruleset;
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}
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if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
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if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
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goto err_close_ruleset;
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}
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if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
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LANDLOCK_ACCESS_NET_BIND_TCP)) {
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goto err_close_ruleset;
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}
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if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
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LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
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goto err_close_ruleset;
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}
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if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
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perror("Failed to restrict privileges");
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goto err_close_ruleset;
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