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samples/landlock: Support TCP restrictions
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Add TCP restrictions to the sandboxer demo. It's possible to allow a
sandboxer to bind/connect to a list of specified ports restricting
network actions to the rest of them. This is controlled with the new
LL_TCP_BIND and LL_TCP_CONNECT environment variables.

Rename ENV_PATH_TOKEN to ENV_DELIMITER.

Signed-off-by: Konstantin Meskhidze <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[mic: Extend commit message]
Signed-off-by: Mickaël Salaün <[email protected]>
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@BoardzMaster @l0kod
BoardzMaster authored and l0kod committed Oct 26, 2023
1 parent a549d05 commit 5e990dc
Showing 1 changed file with 100 additions and 15 deletions.
115 changes: 100 additions & 15 deletions samples/landlock/sandboxer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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)
{
Expand All @@ -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;
}
Expand All @@ -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;
Expand Down Expand Up @@ -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 ( \
Expand All @@ -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",
Expand Down Expand Up @@ -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 "
Expand All @@ -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;
Expand Down

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