[PATCH v10 09/13] landlock: Add network rules and TCP hooks support

[Mickaël Salaün]

On 23/03/2023 09:52, Konstantin Meskhidze wrote:
> This commit adds network rules support in the ruleset management
> helpers and the landlock_create_ruleset syscall.
> Refactor user space API to support network actions. Add new network
> access flags, network rule and network attributes. Increment Landlock
> ABI version. Expand access_masks_t to u32 to be sure network access
> rights can be stored. Implement socket_bind() and socket_connect()
> LSM hooks, which enable to restrict TCP socket binding and connection
> to specific ports.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.com>
> ---
> 
> Changes since v9:
> * Changes UAPI port field to __u64.
> * Moves shared code into check_socket_access().
> * Adds get_raw_handled_net_accesses() and
> get_current_net_domain() helpers.
> * Minor fixes.
> 
> Changes since v8:
> * Squashes commits.
> * Refactors commit message.
> * Changes UAPI port field to __be16.
> * Changes logic of bind/connect hooks with AF_UNSPEC families.
> * Adds address length checking.
> * Minor fixes.
> 
> Changes since v7:
> * Squashes commits.
> * Increments ABI version to 4.
> * Refactors commit message.
> * Minor fixes.
> 
> Changes since v6:
> * Renames landlock_set_net_access_mask() to landlock_add_net_access_mask()
>    because it OR values.
> * Makes landlock_add_net_access_mask() more resilient incorrect values.
> * Refactors landlock_get_net_access_mask().
> * Renames LANDLOCK_MASK_SHIFT_NET to LANDLOCK_SHIFT_ACCESS_NET and use
>    LANDLOCK_NUM_ACCESS_FS as value.
> * Updates access_masks_t to u32 to support network access actions.
> * Refactors landlock internal functions to support network actions with
>    landlock_key/key_type/id types.
> 
> Changes since v5:
> * Gets rid of partial revert from landlock_add_rule
> syscall.
> * Formats code with clang-format-14.
> 
> Changes since v4:
> * Refactors landlock_create_ruleset() - splits ruleset and
> masks checks.
> * Refactors landlock_create_ruleset() and landlock mask
> setters/getters to support two rule types.
> * Refactors landlock_add_rule syscall add_rule_path_beneath
> function by factoring out get_ruleset_from_fd() and
> landlock_put_ruleset().
> 
> Changes since v3:
> * Splits commit.
> * Adds network rule support for internal landlock functions.
> * Adds set_mask and get_mask for network.
> * Adds rb_root root_net_port.
> 
> ---
>   include/uapi/linux/landlock.h                |  49 +++++
>   security/landlock/Kconfig                    |   1 +
>   security/landlock/Makefile                   |   2 +
>   security/landlock/limits.h                   |   6 +-
>   security/landlock/net.c                      | 198 +++++++++++++++++++
>   security/landlock/net.h                      |  26 +++
>   security/landlock/ruleset.c                  |  52 ++++-
>   security/landlock/ruleset.h                  |  63 +++++-
>   security/landlock/setup.c                    |   2 +
>   security/landlock/syscalls.c                 |  72 ++++++-
>   tools/testing/selftests/landlock/base_test.c |   2 +-
>   11 files changed, 450 insertions(+), 23 deletions(-)
>   create mode 100644 security/landlock/net.c
>   create mode 100644 security/landlock/net.h

[...]

> diff --git a/security/landlock/net.c b/security/landlock/net.c

[...]

> +static int check_addrlen(const struct sockaddr *const address, int addrlen)

const int addrlen

> +{
> +	if (addrlen < offsetofend(struct sockaddr, sa_family))
> +		return -EINVAL;
> +	switch (address->sa_family) {
> +	case AF_UNSPEC:
> +	case AF_INET:
> +		if (addrlen < sizeof(struct sockaddr_in))
> +			return -EINVAL;
> +		return 0;
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case AF_INET6:
> +		if (addrlen < SIN6_LEN_RFC2133)
> +			return -EINVAL;
> +		return 0;
> +#endif
> +	}
> +	WARN_ON_ONCE(1);
> +	return 0;
> +}
> +
> +static u16 get_port(const struct sockaddr *const address)
> +{
> +	/* Gets port value in host byte order. */
> +	switch (address->sa_family) {
> +	case AF_UNSPEC:
> +	case AF_INET: {
> +		const struct sockaddr_in *const sockaddr =
> +			(struct sockaddr_in *)address;
> +		return ntohs(sockaddr->sin_port);

Storing ports in big endian (in rulesets) would avoid converting them 
every time the kernel checks a socket port. The above comment should 
then be updated too.


> +	}
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case AF_INET6: {
> +		const struct sockaddr_in6 *const sockaddr_ip6 =
> +			(struct sockaddr_in6 *)address;
> +		return ntohs(sockaddr_ip6->sin6_port);
> +	}
> +#endif
> +	}
> +	WARN_ON_ONCE(1);
> +	return 0;
> +}
> +
> +static int check_socket_access(struct socket *sock, struct sockaddr *address, int addrlen, u16 port,
> +			       access_mask_t access_request)
> +{
> +	int ret;
> +	bool allowed = false;
> +	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_NET] = {};
> +	const struct landlock_rule *rule;
> +	access_mask_t handled_access;
> +	const struct landlock_id id = {
> +		.key.data = port,
> +		.type = LANDLOCK_KEY_NET_PORT,
> +	};
> +	const struct landlock_ruleset *const domain = get_current_net_domain();
> +
> +	if (WARN_ON_ONCE(!domain))
> +		return 0;
> +	if (WARN_ON_ONCE(domain->num_layers < 1))
> +		return -EACCES;
> +	/* Check if it's a TCP socket. */
> +	if (sock->type != SOCK_STREAM)
> +		return 0;
> +
> +	ret = check_addrlen(address, addrlen);
> +	if (ret)
> +		return ret;
> +
> +	switch (address->sa_family) {
> +	case AF_UNSPEC:
> +		/*
> +		 * 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.
> +		 */
> +		if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP)
> +			return 0;
> +
> +		/*
> +		 * For compatibility reason, accept AF_UNSPEC for bind
> +		 * accesses (mapped to AF_INET) only if the address is
> +		 * INADDR_ANY (cf. __inet_bind).  Checking the address is
> +		 * required to not wrongfully return -EACCES instead of
> +		 * -EAFNOSUPPORT.
> +		 */
> +		if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
> +			const struct sockaddr_in *const sockaddr =
> +				(struct sockaddr_in *)address;
> +
> +			if (sockaddr->sin_addr.s_addr != htonl(INADDR_ANY))
> +				return -EAFNOSUPPORT;
> +		}
> +
> +		fallthrough;
> +	case AF_INET:
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case AF_INET6:
> +#endif
> +		rule = landlock_find_rule(domain, id);
> +		handled_access = landlock_init_layer_masks(
> +			domain, access_request, &layer_masks,
> +			LANDLOCK_KEY_NET_PORT);
> +		allowed = landlock_unmask_layers(rule, handled_access,
> +						 &layer_masks,
> +						 ARRAY_SIZE(layer_masks));
> +	}
> +	return allowed ? 0 : -EACCES;
> +}
> +
> +static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
> +			    int addrlen)
> +{
> +	return check_socket_access(sock, address, addrlen, get_port(address),
> +				   LANDLOCK_ACCESS_NET_BIND_TCP);
> +}
> +
> +static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
> +			       int addrlen)
> +{
> +	return check_socket_access(sock, address, addrlen, get_port(address),
> +				   LANDLOCK_ACCESS_NET_CONNECT_TCP);
> +}

[...]