On 16/05/2022 17:20, Konstantin Meskhidze wrote:
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@xxxxxxxxxx>
---
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;
I think network ports should be optional to be able to test without that
(and not break compatibility). You can pass &ruleset_attr as argument to
update it accordingly:
- without environment variable: no network restriction;
- with empty environment variable: all connect (or bind) denied;
- otherwise: only allow the listed ports.
+ }
+ 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);
This is good and will be better with clang-format. ;)
+ 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\" "
Bind ports example should reference unprivileged ports such as "9418"
(git, not well-known but OK).
+ "%s=\"10000:12000\" "
Connect ports example should reference well-known ports such as "80:443".
"%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);
+
Why?
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;
- }
Why? I know that checkpatch.pl prints a warning for that but I
delibirately chooe to use curly braces even for "if" statements with one
line because it is safer. This code may be copied/pasted and I'd like
others to avoid introducing goto-fail-like issues.
- 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))
So please use curly braces here too.
+ 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;
What‽
/* 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
