[PATCH v10 09/13] landlock: Add network rules and TCP hooks support
Mickaël Salaün
mic at digikod.net
Thu Apr 6 10:28:26 UTC 2023
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,
};
>>
>>> 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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