Re: [PATCH v10 09/13] landlock: Add network rules and TCP hooks support

["Konstantin Meskhidze (A)" <konstantin.meskhidze@huawei.com>]

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@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);
>>>>>> +}
>>>>>
>>>>> [...]
>>>>> .
> .