[PATCH v4 6/7] samples/landlock: Add sandboxer UDP access control

Matthieu Buffet
2026-05-02T12:44:41Z

Add environment variables to control associated access rights:
- LL_UDP_BIND
- LL_UDP_CONNECT_SEND

Each one takes a list of ports separated by colons, like other list
options.

Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
---
samples/landlock/sandboxer.c | 40 ++++++++++++++++++++++++++++++++++--
1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index 66e56ae275c6..94e399e6b146 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -62,6 +62,8 @@ static inline int landlock_restrict_self(const int ruleset_fd,
#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
#define ENV_SCOPED_NAME "LL_SCOPED"
#define ENV_FORCE_LOG_NAME "LL_FORCE_LOG"
+#define ENV_UDP_BIND_NAME "LL_UDP_BIND"
+#define ENV_UDP_CONNECT_SEND_NAME "LL_UDP_CONNECT_SEND"
#define ENV_DELIMITER ":"

static int str2num(const char *numstr, __u64 *num_dst)
@@ -301,7 +303,7 @@ static bool check_ruleset_scope(const char *const env_var,

/* clang-format on */

-#define LANDLOCK_ABI_LAST 9
+#define LANDLOCK_ABI_LAST 10

#define XSTR(s) #s
#define STR(s) XSTR(s)
@@ -324,6 +326,10 @@ static const char help[] =
"means an empty list):\n"
"* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n"
"* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n"
+ "* " ENV_UDP_BIND_NAME ": local UDP ports allowed to bind (server: "
+ "prepare to receive on port / client: set as source port)\n"
+ "* " ENV_UDP_CONNECT_SEND_NAME ": remote UDP ports allowed to connect "
+ "or sendmsg (client: use as destination port / server: receive only from it)\n"
"* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n"
" - \"a\" to restrict opening abstract unix sockets\n"
" - \"s\" to restrict sending signals\n"
@@ -336,6 +342,7 @@ static const char help[] =
ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
ENV_TCP_BIND_NAME "=\"9418\" "
ENV_TCP_CONNECT_NAME "=\"80:443\" "
+ ENV_UDP_CONNECT_SEND_NAME "=\"53\" "
ENV_SCOPED_NAME "=\"a:s\" "
"%1$s bash -i\n"
"\n"
@@ -356,7 +363,9 @@ int main(const int argc, char *const argv[], char *const *const envp)
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,
+ LANDLOCK_ACCESS_NET_CONNECT_TCP |
+ LANDLOCK_ACCESS_NET_BIND_UDP |
+ LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP,
.scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
LANDLOCK_SCOPE_SIGNAL,
};
@@ -444,6 +453,13 @@ int main(const int argc, char *const argv[], char *const *const envp)
/* Removes LANDLOCK_ACCESS_FS_RESOLVE_UNIX for ABI < 9 */
ruleset_attr.handled_access_fs &=
~LANDLOCK_ACCESS_FS_RESOLVE_UNIX;
+ __attribute__((fallthrough));
+ case 9:
+ /* Removes UDP support for ABI < 10 */
+ ruleset_attr.handled_access_net &=
+ ~(LANDLOCK_ACCESS_NET_BIND_UDP |
+ LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP);
+
/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
fprintf(stderr,
"Hint: You should update the running kernel "
@@ -475,6 +491,18 @@ int main(const int argc, char *const argv[], char *const *const envp)
ruleset_attr.handled_access_net &=
~LANDLOCK_ACCESS_NET_CONNECT_TCP;
}
+ /* Removes UDP bind access control if not supported by a user. */
+ env_port_name = getenv(ENV_UDP_BIND_NAME);
+ if (!env_port_name) {
+ ruleset_attr.handled_access_net &=
+ ~LANDLOCK_ACCESS_NET_BIND_UDP;
+ }
+ /* Removes UDP connect/send access control if not supported by a user. */
+ env_port_name = getenv(ENV_UDP_CONNECT_SEND_NAME);
+ if (!env_port_name) {
+ ruleset_attr.handled_access_net &=
+ ~LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP;
+ }

if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr))
return 1;
@@ -519,6 +547,14 @@ int main(const int argc, char *const argv[], char *const *const envp)
LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
goto err_close_ruleset;
}
+ if (populate_ruleset_net(ENV_UDP_BIND_NAME, ruleset_fd,
+ LANDLOCK_ACCESS_NET_BIND_UDP)) {
+ goto err_close_ruleset;
+ }
+ if (populate_ruleset_net(ENV_UDP_CONNECT_SEND_NAME, ruleset_fd,
+ LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP)) {
+ goto err_close_ruleset;
+ }

if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
perror("Failed to restrict privileges");
--
2.39.5