[PATCH v10 09/13] landlock: Add network rules and TCP hooks support
Mickaël Salaün
mic at digikod.net
Tue Apr 4 16:42:57 UTC 2023
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 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.
>>
>>
>>> + }
>>> +#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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