Date:   Tue, 14 Mar 2023 17:38:33 +0300
From:   "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>
To:     Mickaël Salaün <mic@...ikod.net>
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



3/14/2023 3:13 PM, Mickaël Salaün пишет:
> 
> 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.

   Ok. Will be renamed..
> .

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