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

["Mickaël Salaün" <mic@digikod.net>]

On 31/03/2023 19:24, Mickaël Salaün wrote:
> 
> 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@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.

You can then return a __be16 type here and at least also use __be16 in 
check_socket_access().

> 
> 
>> +	}
>> +#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);
>> +}
> 
> [...]