Re: [PATCH v8 11/12] samples/landlock: Add network demo

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11/16/2022 5:25 PM, Mickaël Salaün пишет:

On 21/10/2022 17:26, Konstantin Meskhidze wrote:
This commit adds network 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@xxxxxxxxxx>
---

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 | 129 +++++++++++++++++++++++++++++++----
  1 file changed, 116 insertions(+), 13 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index fd4237c64fb2..68582b0d7c85 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 ( \
@@ -81,8 +97,8 @@ 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 +159,48 @@ 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) {
+		ret = 0;
+		goto out_free_name;

This is a bug because env_port_name is not allocated. This should simply
return 0.


+	}
+	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 ( \
@@ -164,41 +222,63 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
  	LANDLOCK_ACCESS_FS_REFER | \
  	LANDLOCK_ACCESS_FS_TRUNCATE)

+#define ACCESS_NET_BIND_CONNECT ( \
+	LANDLOCK_ACCESS_NET_BIND_TCP | \
+	LANDLOCK_ACCESS_NET_CONNECT_TCP)

You can remove ACCESS_NET_BIND_CONNECT and make the underlying access
rights explicit.


+
  /* 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;
+	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE,
+	      access_net_tcp = ACCESS_NET_BIND_CONNECT;
  	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);
  		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",
@@ -240,7 +320,10 @@ 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 &= ~ACCESS_NET_BIND_CONNECT;

You can check the TCP environment variables here and error out if one is
set.

Please keep the newline here.


  		fprintf(stderr,
  			"Hint: You should update the running kernel "
  			"to leverage Landlock features "
@@ -259,16 +342,36 @@ 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) {

You can move this logic at the populate_ruleset_net() call site and
update this helper to not call getenv() twice for the same variable.

  But here I exclude ruleset attributes, not rule itself. It will break
  the logic: creating a ruleset then applying rules.
  I suggest to leave here as its.


+		access_net_tcp &= ~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) {
+		access_net_tcp &= ~LANDLOCK_ACCESS_NET_CONNECT_TCP;
+	}
+	ruleset_attr.handled_access_net &= access_net_tcp;

There is no need for access_net_tcp.

+
  	ruleset_fd =
  		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
  	if (ruleset_fd < 0) {
  		perror("Failed to create a ruleset");
  		return 1;
  	}

newline

-	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;
+	}

newline

+	if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_BIND_TCP)) {
  		goto err_close_ruleset;
  	}
-	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
+	if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
  		goto err_close_ruleset;
  	}

newline

  	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
--
2.25.1

.



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