landlock: Log TCP bind and connect denials

Add audit support to socket_bind and socket_connect hooks.

The related blockers are:
- net.bind_tcp
- net.connect_tcp

Audit event sample:

  type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=net.connect_tcp daddr=127.0.0.1 dest=80

Cc: Günther Noack <gnoack@google.com>
Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-16-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

security/landlock/audit.c

@@ -41,6 +41,13 @@ static const char *const fs_access_strings[] = {
 
 static_assert(ARRAY_SIZE(fs_access_strings) == LANDLOCK_NUM_ACCESS_FS);
 
+static const char *const net_access_strings[] = {
+	[BIT_INDEX(LANDLOCK_ACCESS_NET_BIND_TCP)] = "net.bind_tcp",
+	[BIT_INDEX(LANDLOCK_ACCESS_NET_CONNECT_TCP)] = "net.connect_tcp",
+};
+
+static_assert(ARRAY_SIZE(net_access_strings) == LANDLOCK_NUM_ACCESS_NET);
+
 static __attribute_const__ const char *
 get_blocker(const enum landlock_request_type type,
 	    const unsigned long access_bit)
@@ -58,6 +65,11 @@ get_blocker(const enum landlock_request_type type,
 		if (WARN_ON_ONCE(access_bit >= ARRAY_SIZE(fs_access_strings)))
 			return "unknown";
 		return fs_access_strings[access_bit];
+
+	case LANDLOCK_REQUEST_NET_ACCESS:
+		if (WARN_ON_ONCE(access_bit >= ARRAY_SIZE(net_access_strings)))
+			return "unknown";
+		return net_access_strings[access_bit];
 	}
 
 	WARN_ON_ONCE(1);

security/landlock/audit.h

@@ -18,6 +18,7 @@ enum landlock_request_type {
 	LANDLOCK_REQUEST_PTRACE = 1,
 	LANDLOCK_REQUEST_FS_CHANGE_TOPOLOGY,
 	LANDLOCK_REQUEST_FS_ACCESS,
+	LANDLOCK_REQUEST_NET_ACCESS,
 };
 
 /*

security/landlock/net.c

@@ -7,10 +7,12 @@
  */
 
 #include <linux/in.h>
+#include <linux/lsm_audit.h>
 #include <linux/net.h>
 #include <linux/socket.h>
 #include <net/ipv6.h>
 
+#include "audit.h"
 #include "common.h"
 #include "cred.h"
 #include "limits.h"
@@ -55,6 +57,7 @@ static int current_check_access_socket(struct socket *const sock,
 	};
 	const struct landlock_cred_security *const subject =
 		landlock_get_applicable_subject(current_cred(), masks, NULL);
+	struct lsm_network_audit audit_net = {};
 
 	if (!subject)
 		return 0;
@@ -68,18 +71,48 @@ static int current_check_access_socket(struct socket *const sock,
 
 	switch (address->sa_family) {
 	case AF_UNSPEC:
-	case AF_INET:
+	case AF_INET: {
+		const struct sockaddr_in *addr4;
+
 		if (addrlen < sizeof(struct sockaddr_in))
 			return -EINVAL;
-		port = ((struct sockaddr_in *)address)->sin_port;
+
+		addr4 = (struct sockaddr_in *)address;
+		port = addr4->sin_port;
+
+		if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP) {
+			audit_net.dport = port;
+			audit_net.v4info.daddr = addr4->sin_addr.s_addr;
+		} else if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
+			audit_net.sport = port;
+			audit_net.v4info.saddr = addr4->sin_addr.s_addr;
+		} else {
+			WARN_ON_ONCE(1);
+		}
 		break;
+	}
 
 #if IS_ENABLED(CONFIG_IPV6)
-	case AF_INET6:
+	case AF_INET6: {
+		const struct sockaddr_in6 *addr6;
+
 		if (addrlen < SIN6_LEN_RFC2133)
 			return -EINVAL;
-		port = ((struct sockaddr_in6 *)address)->sin6_port;
+
+		addr6 = (struct sockaddr_in6 *)address;
+		port = addr6->sin6_port;
+
+		if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP) {
+			audit_net.dport = port;
+			audit_net.v6info.daddr = addr6->sin6_addr;
+		} else if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
+			audit_net.sport = port;
+			audit_net.v6info.saddr = addr6->sin6_addr;
+		} else {
+			WARN_ON_ONCE(1);
+		}
 		break;
+	}
 #endif /* IS_ENABLED(CONFIG_IPV6) */
 
 	default:
@@ -149,6 +182,16 @@ static int current_check_access_socket(struct socket *const sock,
 				   ARRAY_SIZE(layer_masks)))
 		return 0;
 
+	audit_net.family = address->sa_family;
+	landlock_log_denial(subject,
+			    &(struct landlock_request){
+				    .type = LANDLOCK_REQUEST_NET_ACCESS,
+				    .audit.type = LSM_AUDIT_DATA_NET,
+				    .audit.u.net = &audit_net,
+				    .access = access_request,
+				    .layer_masks = &layer_masks,
+				    .layer_masks_size = ARRAY_SIZE(layer_masks),
+			    });
 	return -EACCES;
 }