[RFC PATCH v3 7/8] samples/landlock: Add sandboxer UDP access control

[Matthieu Buffet <matthieu@buffet.re>]

Add environment variables to control associated access rights:
- LL_UDP_BIND
- LL_UDP_CONNECT
- LL_UDP_SENDTO

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 | 58 ++++++++++++++++++++++++++++++++++--
 1 file changed, 56 insertions(+), 2 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index e7af02f98208..65accc095926 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -62,6 +62,9 @@ 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_NAME "LL_UDP_CONNECT"
+#define ENV_UDP_SENDTO_NAME "LL_UDP_SENDTO"
 #define ENV_DELIMITER ":"
 
 static int str2num(const char *numstr, __u64 *num_dst)
@@ -299,7 +302,7 @@ static bool check_ruleset_scope(const char *const env_var,
 
 /* clang-format on */
 
-#define LANDLOCK_ABI_LAST 7
+#define LANDLOCK_ABI_LAST 8
 
 #define XSTR(s) #s
 #define STR(s) XSTR(s)
@@ -322,6 +325,12 @@ 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_NAME ": remote UDP ports allowed to connect "
+	"(client: set as destination port / server: receive only from it)\n"
+	"* " ENV_UDP_SENDTO_NAME ": remote UDP ports allowed to send to "
+	"without prior connect()\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"
@@ -334,6 +343,8 @@ 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_NAME "=\"53\" "
+	ENV_UDP_SENDTO_NAME "=\"53\" "
 	ENV_SCOPED_NAME "=\"a:s\" "
 	"%1$s bash -i\n"
 	"\n"
@@ -354,7 +365,10 @@ 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_UDP |
+				      LANDLOCK_ACCESS_NET_SENDTO_UDP,
 		.scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
 			  LANDLOCK_SCOPE_SIGNAL,
 	};
@@ -436,6 +450,13 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		/* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */
 		supported_restrict_flags &=
 			~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
+		__attribute__((fallthrough));
+	case 7:
+		/* Removes UDP support for ABI < 8 */
+		ruleset_attr.handled_access_net &=
+			~(LANDLOCK_ACCESS_NET_BIND_UDP |
+			  LANDLOCK_ACCESS_NET_CONNECT_UDP |
+			  LANDLOCK_ACCESS_NET_SENDTO_UDP);
 
 		/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
 		fprintf(stderr,
@@ -468,6 +489,27 @@ 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 access control if not supported by a user. */
+	env_port_name = getenv(ENV_UDP_CONNECT_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_CONNECT_UDP;
+	}
+	/*
+	 * Removes UDP send with explicit address access control if not
+	 * supported by a user.
+	 */
+	env_port_name = getenv(ENV_UDP_SENDTO_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_SENDTO_UDP;
+	}
 
 	if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr))
 		return 1;
@@ -512,6 +554,18 @@ 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_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_CONNECT_UDP)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset_net(ENV_UDP_SENDTO_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_SENDTO_UDP)) {
+		goto err_close_ruleset;
+	}
 
 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
 		perror("Failed to restrict privileges");
-- 
2.47.3