Message-ID: <59356a12-75cf-32d3-ea76-daafd0788af6@digikod.net>
Date:   Tue, 14 Mar 2023 13:13:31 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>
Cc:     willemdebruijn.kernel@...il.com, gnoack3000@...il.com,
        linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, yusongping@...wei.com,
        artem.kuzin@...wei.com
Subject: Re: [PATCH v9 08/12] landlock: Add network rules and TCP hooks
 support


On 13/03/2023 10:33, Konstantin Meskhidze (A) wrote:
> 
> 
> 2/10/2023 8:39 PM, Mickaël Salaün пишет:
>>
>> On 16/01/2023 09:58, 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@...wei.com>
>>> ---
>>>
>>> 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.
>>
>> [...]
>>
>>> +static int check_socket_access(const struct landlock_ruleset *const domain,
>>> +			       struct sockaddr *address, __be16 port,
>>> +			       access_mask_t access_request)
>>> +{
>>> +	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,
>>> +	};
>>> +
>>> +	if (WARN_ON_ONCE(!domain))
>>> +		return 0;
>>> +	if (WARN_ON_ONCE(domain->num_layers < 1))
>>> +		return -EACCES;
>>> +
>>> +	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));
>>> +
>>> +		fallthrough;
>>
>> You can remove this fallthrough.
>>
>>
>>> +	}
>>> +	return allowed ? 0 : -EACCES;
>>> +}
>>> +
>>> +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 sockaddr->sin_port;
>>> +	}
>>> +#if IS_ENABLED(CONFIG_IPV6)
>>> +	case AF_INET6: {
>>> +		const struct sockaddr_in6 *const sockaddr_ip6 =
>>> +			(struct sockaddr_in6 *)address;
>>> +		return sockaddr_ip6->sin6_port;
>>> +	}
>>> +#endif
>>> +	}
>>> +	WARN_ON_ONCE(1);
>>> +	return 0;
>>> +}
>>> +
>>> +static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
>>> +			    int addrlen)
>>> +{
>>> +	int ret;
>>> +	const struct landlock_ruleset *const dom =
>>> +		landlock_get_current_domain();
>>
>> landlock_get_current_domain() should only be called by a
>> get_current_net_domain() wrapper that checks if the current domain
>> handles network accesses. See get_current_fs_domain() in patch 2/12.
> 
>     Hi Mickaël.
>     I have question:
> 
>     static access_mask_t
> get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
> {
> 	access_mask_t access_dom = 0;
> 	size_t layer_level;
> 
> 	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> 		access_dom |=
> 			landlock_get_raw_fs_access_mask(domain, layer_level);
> 	return access_dom & LANDLOCK_MASK_ACCESS_FS;
> }
> 
> landlock_get_raw_fs_access_mask() function is already mask by
> LANDLOCK_MASK_ACCESS_FS. We could get rid of access_dom masking.
> What do you think?

Right, you can remove this extra mask.

While reading the code again I found that it would be better to rename 
ACCESS_FS_INITIALLY_DENIED to LANDLOCK_ACCESS_FS_INITIALLY_DENIED.

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