net.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Landlock - Network management and hooks
 *
 * Copyright © 2022-2023 Huawei Tech. Co., Ltd.
 * Copyright © 2022-2025 Microsoft Corporation
 */

#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"
#include "net.h"
#include "ruleset.h"

int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
			     const u16 port, access_mask_t access_rights)
{
	int err;
	const struct landlock_id id = {
		.key.data = (__force uintptr_t)htons(port),
		.type = LANDLOCK_KEY_NET_PORT,
	};

	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));

	/* Transforms relative access rights to absolute ones. */
	access_rights |= LANDLOCK_MASK_ACCESS_NET &
			 ~landlock_get_net_access_mask(ruleset, 0);

	mutex_lock(&ruleset->lock);
	err = landlock_insert_rule(ruleset, id, access_rights);
	mutex_unlock(&ruleset->lock);

	return err;
}

static int current_check_access_socket(struct socket *const sock,
				       struct sockaddr *const address,
				       const int addrlen,
				       access_mask_t access_request)
{
	__be16 port;
	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_NET] = {};
	const struct landlock_rule *rule;
	struct landlock_id id = {
		.type = LANDLOCK_KEY_NET_PORT,
	};
	const struct access_masks masks = {
		.net = access_request,
	};
	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;

	if (!sk_is_tcp(sock->sk))
		return 0;

	/* Checks for minimal header length to safely read sa_family. */
	if (addrlen < offsetofend(typeof(*address), sa_family))
		return -EINVAL;

	switch (address->sa_family) {
	case AF_UNSPEC:
		if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP) {
			/*
			 * Connecting to an address with AF_UNSPEC dissolves
			 * the TCP association, which have the same effect as
			 * closing the connection while retaining the socket
			 * object (i.e., the file descriptor).  As for dropping
			 * privileges, closing connections is always allowed.
			 *
			 * For a TCP access control system, this request is
			 * legitimate. Let the network stack handle potential
			 * inconsistencies and return -EINVAL if needed.
			 */
			return 0;
		} else if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
			/*
			 * Binding to an AF_UNSPEC address is treated
			 * differently by IPv4 and IPv6 sockets. The socket's
			 * family may change under our feet due to
			 * setsockopt(IPV6_ADDRFORM), but that's ok: we either
			 * reject entirely or require
			 * %LANDLOCK_ACCESS_NET_BIND_TCP for the given port, so
			 * it cannot be used to bypass the policy.
			 *
			 * IPv4 sockets map AF_UNSPEC to AF_INET for
			 * retrocompatibility for bind accesses, only if the
			 * address is INADDR_ANY (cf. __inet_bind). IPv6
			 * sockets always reject it.
			 *
			 * Checking the address is required to not wrongfully
			 * return -EACCES instead of -EAFNOSUPPORT or -EINVAL.
			 * We could return 0 and let the network stack handle
			 * these checks, but it is safer to return a proper
			 * error and test consistency thanks to kselftest.
			 */
			if (sock->sk->__sk_common.skc_family == AF_INET) {
				const struct sockaddr_in *const sockaddr =
					(struct sockaddr_in *)address;

				if (addrlen < sizeof(struct sockaddr_in))
					return -EINVAL;

				if (sockaddr->sin_addr.s_addr !=
				    htonl(INADDR_ANY))
					return -EAFNOSUPPORT;
			} else {
				if (addrlen < SIN6_LEN_RFC2133)
					return -EINVAL;
				else
					return -EAFNOSUPPORT;
			}
		} else {
			WARN_ON_ONCE(1);
		}
		/* Only for bind(AF_UNSPEC+INADDR_ANY) on IPv4 socket. */
		fallthrough;
	case AF_INET: {
		const struct sockaddr_in *addr4;

		if (addrlen < sizeof(struct sockaddr_in))
			return -EINVAL;

		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: {
		const struct sockaddr_in6 *addr6;

		if (addrlen < SIN6_LEN_RFC2133)
			return -EINVAL;

		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:
		return 0;
	}

	/*
	 * Checks sa_family consistency to not wrongfully return
	 * -EACCES instead of -EINVAL.  Valid sa_family changes are
	 * only (from AF_INET or AF_INET6) to AF_UNSPEC.
	 *
	 * We could return 0 and let the network stack handle this
	 * check, but it is safer to return a proper error and test
	 * consistency thanks to kselftest.
	 */
	if (address->sa_family != sock->sk->__sk_common.skc_family &&
	    address->sa_family != AF_UNSPEC)
		return -EINVAL;

	id.key.data = (__force uintptr_t)port;
	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));

	rule = landlock_find_rule(subject->domain, id);
	access_request = landlock_init_layer_masks(subject->domain,
						   access_request, &layer_masks,
						   LANDLOCK_KEY_NET_PORT);
	if (landlock_unmask_layers(rule, access_request, &layer_masks,
				   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;
}

static int hook_socket_bind(struct socket *const sock,
			    struct sockaddr *const address, const int addrlen)
{
	return current_check_access_socket(sock, address, addrlen,
					   LANDLOCK_ACCESS_NET_BIND_TCP);
}

static int hook_socket_connect(struct socket *const sock,
			       struct sockaddr *const address,
			       const int addrlen)
{
	return current_check_access_socket(sock, address, addrlen,
					   LANDLOCK_ACCESS_NET_CONNECT_TCP);
}

static struct security_hook_list landlock_hooks[] __ro_after_init = {
	LSM_HOOK_INIT(socket_bind, hook_socket_bind),
	LSM_HOOK_INIT(socket_connect, hook_socket_connect),
};

__init void landlock_add_net_hooks(void)
{
	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
			   &landlock_lsmid);
}