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.
+ 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
.
