[PATCH v10 09/13] landlock: Add network rules and TCP hooks support
Konstantin Meskhidze (A)
konstantin.meskhidze at huawei.com
Wed Apr 5 17:42:29 UTC 2023
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));
...
????
>
>> 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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