[PATCH v14 11/12] samples/landlock: Support TCP restrictions

[Konstantin Meskhidze <konstantin.meskhidze@huawei.com>]

Add TCP restrictions to the sandboxer demo. It's possible
to allow a sandboxer to bind/connect to a list of particular
ports restricting network actions to the rest of ports.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---

Changes since v13:
* Refactors commit message.

Changes since v12:
* Defines __SANE_USERSPACE_TYPES__ to avoid warnings for PowerPC.

Changes since v11:
* Changes ENV_PATH_TOKEN to ENV_DELIMITER.
* Refactors populate_ruleset_net():
  - Deletes parse_port_num() helper.
  - Uses strsep() instead of strtok().
* Fixes wrong printf format.

Changes since v10:
* Refactors populate_ruleset_net() helper.
* Code style minor fix.

Changes since v9:
* Deletes ports converting.
* Minor fixes.

Changes since v8:
* Convert ports to __be16.
* Minor fixes.

Changes since v7:
* Removes network support if ABI < 4.
* Removes network support if not set by a user.

Changes since v6:
* Removes network support if ABI < 3.

Changes since v5:
* Makes network ports sandboxing optional.
* Fixes some logic errors.
* Formats code with clang-format-14.

Changes since v4:
* Adds ENV_TCP_BIND_NAME "LL_TCP_BIND" and
ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" variables
to insert TCP ports.
* Renames populate_ruleset() to populate_ruleset_fs().
* Adds populate_ruleset_net() and parse_port_num() helpers.
* Refactors main() to support network sandboxing.

---
 samples/landlock/sandboxer.c | 115 ++++++++++++++++++++++++++++++-----
 1 file changed, 100 insertions(+), 15 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index e2056c8b902c..08596c0ef070 100644
--- 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 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
 	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 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,

 /* 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;
--
2.25.1