[PATCH v9 08/12] landlock: Add network rules and TCP hooks support
Mickaël Salaün
mic at digikod.net
Tue Mar 14 12:13:31 UTC 2023
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 at huawei.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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