[PATCH v10 09/13] landlock: Add network rules and TCP hooks support
Konstantin Meskhidze (A)
konstantin.meskhidze at huawei.com
Thu Apr 6 10:30:32 UTC 2023
4/6/2023 1:28 PM, Mickaël Salaün пишет:
>
> On 05/04/2023 19:42, Konstantin Meskhidze (A) wrote:
>>
>>
>> 4/4/2023 7:42 PM, Mickaël Salaün пишет:
>>>
>>> On 04/04/2023 11:31, Konstantin Meskhidze (A) wrote:
>>>>
>>>>
>>>> 3/31/2023 8:24 PM, Mickaël Salaün пишет:
>>>>>
>>>>> 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
>>>>
>>>> Got it.
>>>>>
>>>>>> +{
>>>>>> + 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.
>>>>
>>>> I thought we came to a conclusion to stick to host endianess and
>>>> let kernel do the checks under the hood:
>>>> https://lore.kernel.org/linux-security-module/278ab07f-7583-a4e0-3d37-1bacd091531d@digikod.net/
>>>>
>>>> Did I misunderstand something?
>>>
>>> We indeed stick to the host endianess for the UAPI/syscalls, but
>>> internally the kernel has to do the conversion with as it is currently
>>> done by calling ntohs(). To avoid calling ntohs() every time get_port()
>>> is called, we can instead only call htons() when creating rules (i.e.
>>> one-time htons call instead of multiple ntohs calls).
>>>
>> Do you mean we need to covert port in landlock_append_net_rule():
>>
>> ...
>>
>> int err;
>> const struct landlock_id id = {
>> .key.data = ntohs(port),
>> .type = LANDLOCK_KEY_NET_PORT,
>> };
>> BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
>> ...
>> ????
>
> landlock_append_net_rule() takes a u16 (host endianess, which is the
> case with this patch series) and should store a big endian 16-bit
> integer. See my patch:
>
> const struct landlock_id id = {
> - .key.data = port,
> + .key.data = (__force uintptr_t)htons(port),
> .type = LANDLOCK_KEY_NET_PORT,
> };
>
Thanks. Already took a look.
>
>
>>>
>>>> Do you mean we need to do port converting __be16 -> u16 in
>>>> check_socket_access()???
>>>
>>> Removing the ntohs() call from get_port() enables to return __be16
>>> instead of u16, and check_socket_access() will then need to use the same
>>> type.
>>
>> Ok. I got it. Thanks.
>>>
>>>
>>>>>
>>>>>
>>>>>> + }
>>>>>> +#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);
>>>
>>> get_port() is called before check_addrlen(), which is an issue.
>>>
>>> You'll find attached a patch for these fixes, please squash it in this
>>> one for the next version.
>>>
>>> I'll send other reviews by the end of the week.
>>>
>>>
>>>>>> +}
>>>>>> +
>>>>>> +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);
>>>>>> +}
>>>>>
>>>>> [...]
>>>>> .
> .
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