[PATCH v5 15/15] samples/landlock: adds network demo

Konstantin Meskhidze konstantin.meskhidze at huawei.com
Mon May 16 15:20:38 UTC 2022


This commit adds network demo. It's possible to
allow a sandoxer to bind/connect to a list of
particular ports restricting networks actions to
the rest of ports.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.com>
---

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.
* Refactoring main() to support network sandboxing.

---
 samples/landlock/sandboxer.c | 105 +++++++++++++++++++++++++++++++----
 security/landlock/ruleset.h  |   4 +-
 2 files changed, 95 insertions(+), 14 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index 3e404e51ec64..4006c42eec1c 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -51,6 +51,8 @@ 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_TCP_BIND_NAME "LL_TCP_BIND"
+#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
 #define ENV_PATH_TOKEN ":"

 static int parse_path(char *env_path, const char ***const path_list)
@@ -71,6 +73,20 @@ static int parse_path(char *env_path, const char ***const path_list)
 	return num_paths;
 }

+static int parse_port_num(char *env_port)
+{
+	int i, num_ports = 0;
+
+	if (env_port) {
+		num_ports++;
+		for (i = 0; env_port[i]; i++) {
+			if (env_port[i] == ENV_PATH_TOKEN[0])
+				num_ports++;
+		}
+	}
+	return num_ports;
+}
+
 /* clang-format off */

 #define ACCESS_FILE ( \
@@ -80,7 +96,7 @@ 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,
+static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
 			    const __u64 allowed_access)
 {
 	int num_paths, i, ret = 1;
@@ -142,6 +158,49 @@ 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 num_ports, i, ret = 1;
+	char *env_port_name;
+	struct landlock_net_service_attr net_service = {
+		.allowed_access = 0,
+		.port = 0,
+	};
+
+	env_port_name = getenv(env_var);
+	if (!env_port_name) {
+		/* Prevents users to forget a setting. */
+		fprintf(stderr, "Missing environment variable %s\n", env_var);
+		return 1;
+	}
+	env_port_name = strdup(env_port_name);
+	unsetenv(env_var);
+	num_ports = parse_port_num(env_port_name);
+
+	if (num_ports == 1 && (strtok(env_port_name, ENV_PATH_TOKEN) == NULL)) {
+		ret = 0;
+		goto out_free_name;
+	}
+
+	for (i = 0; i < num_ports; i++) {
+		net_service.allowed_access = allowed_access;
+		net_service.port = atoi(strsep(&env_port_name, ENV_PATH_TOKEN));
+		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE,
+					&net_service, 0)) {
+			fprintf(stderr, "Failed to update the ruleset with port \"%d\": %s\n",
+					net_service.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 ( \
@@ -173,19 +232,24 @@ int main(const int argc, char *const argv[], char *const *const envp)
 	char *const *cmd_argv;
 	int ruleset_fd, abi;
 	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
-	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
+	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE,
+	      access_net_tcp = LANDLOCK_ACCESS_NET_BIND_TCP |
+					LANDLOCK_ACCESS_NET_CONNECT_TCP;
 	struct landlock_ruleset_attr ruleset_attr = {
 		.handled_access_fs = access_fs_rw,
+		.handled_access_net = access_net_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);
@@ -193,11 +257,19 @@ int main(const int argc, char *const argv[], char *const *const envp)
 			"* %s: list of paths allowed to be used in a read-write way.\n",
 			ENV_FS_RW_NAME);
 		fprintf(stderr,
-			"\nexample:\n"
+			"* %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=\"15000:16000\" "
+			"%s=\"10000:12000\" "
 			"%s bash -i\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]);
 		return 1;
 	}

@@ -234,16 +306,25 @@ int main(const int argc, char *const argv[], char *const *const envp)

 	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(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
+
+	if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw))
 		goto err_close_ruleset;
-	}
+
+	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;
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 916b30b31c06..e1ff40f238a6 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -19,7 +19,7 @@
 #include "limits.h"
 #include "object.h"

-typedef u16 access_mask_t;
+typedef u32 access_mask_t;

 /* Makes sure all filesystem access rights can be stored. */
 static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
@@ -157,7 +157,7 @@ struct landlock_ruleset {
 			 * layers are set once and never changed for the
 			 * lifetime of the ruleset.
 			 */
-			u32 access_masks[];
+			access_mask_t access_masks[];
 		};
 	};
 };
--
2.25.1



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