Date:   Wed, 5 Apr 2023 20:42:29 +0300
From:   "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>
To:     Mickaël Salaün <mic@...ikod.net>
CC:     <willemdebruijn.kernel@...il.com>, <gnoack3000@...il.com>,
        <linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
        <netfilter-devel@...r.kernel.org>, <yusongping@...wei.com>,
        <artem.kuzin@...wei.com>
Subject: Re: [PATCH v10 09/13] landlock: Add network rules and TCP hooks
 support



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@...wei.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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