Re: [PATCH v7 09/18] landlock: implement TCP network hooks

["Mickaël Salaün" <mic@digikod.net>]

On 10/09/2022 22:28, Konstantin Meskhidze (A) wrote:
> 
> 
> 9/6/2022 11:08 AM, Mickaël Salaün пишет:
>>
>> On 29/08/2022 19:03, Konstantin Meskhidze wrote:
>>> This patch adds support of socket_bind() and socket_connect() hooks.
>>> It's possible to restrict binding and connecting of TCP types of
>>> sockets to particular ports. It's just basic idea of how Landlock
>>
>> I guess it's not a basic idea anymore.
> 
>     Got it. Will be fixed.
>>
>>
>>> could support network confinement.
>>>
>>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
>>> ---
>>>
>>> Changes since v6:
>>> * Updates copyright.
>>> * Refactors landlock_append_net_rule() and check_socket_access()
>>>     functions with landlock_id type.
>>>
>>> Changes since v5:
>>> * Fixes some logic errors.
>>> * Formats code with clang-format-14.
>>>
>>> Changes since v4:
>>> * Factors out CONFIG_INET into make file.
>>> * Refactors check_socket_access().
>>> * Adds helper get_port().
>>> * Adds CONFIG_IPV6 in get_port(), hook_socket_bind/connect
>>> functions to support AF_INET6 family.
>>> * Adds AF_UNSPEC family support in hook_socket_bind/connect
>>> functions.
>>> * Refactors add_rule_net_service() and landlock_add_rule
>>> syscall to support network rule inserting.
>>> * Refactors init_layer_masks() to support network rules.
>>>
>>> Changes since v3:
>>> * Splits commit.
>>> * Adds SECURITY_NETWORK in config.
>>> * Adds IS_ENABLED(CONFIG_INET) if a kernel has no INET configuration.
>>> * Adds hook_socket_bind and hook_socket_connect hooks.
>>>
>>> ---
>>>    security/landlock/Kconfig    |   1 +
>>>    security/landlock/Makefile   |   2 +
>>>    security/landlock/net.c      | 161 +++++++++++++++++++++++++++++++++++
>>>    security/landlock/net.h      |  26 ++++++
>>>    security/landlock/setup.c    |   2 +
>>>    security/landlock/syscalls.c |  59 ++++++++++++-
>>>    6 files changed, 248 insertions(+), 3 deletions(-)
>>>    create mode 100644 security/landlock/net.c
>>>    create mode 100644 security/landlock/net.h
>>>
>>> diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
>>> index 8e33c4e8ffb8..10c099097533 100644
>>> --- a/security/landlock/Kconfig
>>> +++ b/security/landlock/Kconfig
>>> @@ -3,6 +3,7 @@
>>>    config SECURITY_LANDLOCK
>>>    	bool "Landlock support"
>>>    	depends on SECURITY && !ARCH_EPHEMERAL_INODES
>>> +	select SECURITY_NETWORK
>>>    	select SECURITY_PATH
>>>    	help
>>>    	  Landlock is a sandboxing mechanism that enables processes to restrict
>>> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
>>> index 7bbd2f413b3e..53d3c92ae22e 100644
>>> --- a/security/landlock/Makefile
>>> +++ b/security/landlock/Makefile
>>> @@ -2,3 +2,5 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
>>>
>>>    landlock-y := setup.o syscalls.o object.o ruleset.o \
>>>    	cred.o ptrace.o fs.o
>>> +
>>> +landlock-$(CONFIG_INET) += net.o
>>> \ No newline at end of file
>>> diff --git a/security/landlock/net.c b/security/landlock/net.c
>>> new file mode 100644
>>> index 000000000000..0d249ad619bf
>>> --- /dev/null
>>> +++ b/security/landlock/net.c
>>> @@ -0,0 +1,161 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * Landlock LSM - Network management and hooks
>>> + *
>>> + * Copyright © 2022 Huawei Tech. Co., Ltd.
>>> + * Copyright © 2022 Microsoft Corporation
>>> + */
>>> +
>>> +#include <linux/in.h>
>>> +#include <linux/net.h>
>>> +#include <linux/socket.h>
>>> +#include <net/ipv6.h>
>>> +
>>
>> #include "common.h"
> 
>     This include is in net.h one.

There is no use of it in net.h it should only be here.


>>
>>> +#include "cred.h"
>>> +#include "limits.h"
>>> +#include "net.h"
>>
>> #include "ruleset.h"
> 
>     The same as above.

ruleset.h should be included both in net.h and net.c because it is used 
in both.


>>
>>> +
>>> +int landlock_append_net_rule(struct landlock_ruleset *const ruleset, u16 port,
>>> +			     u32 access_rights)
>>
>> Please constify all arguments, in this function and others.
> 
>     Ok. Thanks.
>>
>>> +{
>>> +	int err;
>>> +	const struct landlock_id id = {
>>> +		.key.data = port,
>>> +		.type = LANDLOCK_KEY_NET_PORT,
>>> +	};
>>> +	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
>>> +
>>> +	/* Transforms relative access rights to absolute ones. */
>>> +	access_rights |= LANDLOCK_MASK_ACCESS_NET &
>>> +			 ~landlock_get_net_access_mask(ruleset, 0);
>>> +
>>> +	mutex_lock(&ruleset->lock);
>>> +	err = landlock_insert_rule(ruleset, id, access_rights);
>>> +	mutex_unlock(&ruleset->lock);
>>> +
>>> +	return err;
>>> +}
>>> +
>>> +static int check_socket_access(const struct landlock_ruleset *const domain,
>>> +			       u16 port, access_mask_t access_request)
>>> +{
>>> +	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,
>>> +	};
>>> +
>>> +	if (WARN_ON_ONCE(!domain))
>>> +		return 0;
>>> +	if (WARN_ON_ONCE(domain->num_layers < 1))
>>> +		return -EACCES;
>>> +
>>> +	rule = landlock_find_rule(domain, id);
>>> +	handled_access = init_layer_masks(domain, access_request, &layer_masks,
>>> +					  LANDLOCK_KEY_NET_PORT);
>>> +	allowed = unmask_layers(rule, handled_access, &layer_masks,
>>> +				ARRAY_SIZE(layer_masks));
>>> +
>>> +	return allowed ? 0 : -EACCES;
>>> +}
>>> +
>>> +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);
>>> +	}
>>> +#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 hook_socket_bind(struct socket *sock, struct sockaddr *address,
>>> +			    int addrlen)
>>> +{
>>> +	const struct landlock_ruleset *const dom =
>>> +		landlock_get_current_domain();
>>> +
>>> +	if (!dom)
>>> +		return 0;
>>> +
>>> +	/* Check if it's a TCP socket. */
>>> +	if (sock->type != SOCK_STREAM)
>>> +		return 0;
>>> +
>>> +	switch (address->sa_family) {
>>> +	case AF_UNSPEC:
>>> +	case AF_INET:
>>> +#if IS_ENABLED(CONFIG_IPV6)
>>> +	case AF_INET6:
>>> +#endif
>>> +		return check_socket_access(dom, get_port(address),
>>> +					   LANDLOCK_ACCESS_NET_BIND_TCP);
>>> +	default:
>>> +		return 0;
>>> +	}
>>> +}
>>> +
>>> +static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
>>> +			       int addrlen)
>>> +{
>>> +	const struct landlock_ruleset *const dom =
>>> +		landlock_get_current_domain();
>>> +
>>> +	if (!dom)
>>> +		return 0;
>>> +
>>> +	/* Check if it's a TCP socket. */
>>> +	if (sock->type != SOCK_STREAM)
>>> +		return 0;
>>> +
>>> +	/* Check if the hook is AF_INET* socket's action. */
>>> +	switch (address->sa_family) {
>>> +	case AF_INET:
>>> +#if IS_ENABLED(CONFIG_IPV6)
>>> +	case AF_INET6:
>>> +#endif
>>> +		return check_socket_access(dom, get_port(address),
>>> +					   LANDLOCK_ACCESS_NET_CONNECT_TCP);
>>> +	case AF_UNSPEC: {
>>> +		u16 i;
>>
>> break line
> 
>     Do you mean adding empty line here?

yes


>>
>>> +		/*
>>> +		 * If just in a layer a mask supports connect access,
>>> +		 * the socket_connect() hook with AF_UNSPEC family flag
>>> +		 * must be banned. This prevents from disconnecting already
>>> +		 * connected sockets.
>>> +		 */
>>> +		for (i = 0; i < dom->num_layers; i++) {
>>> +			if (landlock_get_net_access_mask(dom, i) &
>>> +			    LANDLOCK_ACCESS_NET_CONNECT_TCP)
>>> +				return -EACCES;
>>> +		}
>>> +	}
>>> +	}
>>> +	return 0;
>>> +}
>>> +
>>> +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
>>> +	LSM_HOOK_INIT(socket_bind, hook_socket_bind),
>>> +	LSM_HOOK_INIT(socket_connect, hook_socket_connect),
>>> +};
>>> +
>>> +__init void landlock_add_net_hooks(void)
>>> +{
>>> +	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
>>> +			   LANDLOCK_NAME);
>>> +}
>>> diff --git a/security/landlock/net.h b/security/landlock/net.h
>>> new file mode 100644
>>> index 000000000000..2c63a8f1b258
>>> --- /dev/null
>>> +++ b/security/landlock/net.h
>>> @@ -0,0 +1,26 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Landlock LSM - Network management and hooks
>>> + *
>>> + * Copyright © 2022 Huawei Tech. Co., Ltd.
>>> + */
>>> +
>>> +#ifndef _SECURITY_LANDLOCK_NET_H
>>> +#define _SECURITY_LANDLOCK_NET_H
>>> +
>>> +#include "common.h"
>>> +#include "ruleset.h"
>>> +#include "setup.h"
>>> +
>>> +#if IS_ENABLED(CONFIG_INET)
>>> +__init void landlock_add_net_hooks(void);
>>> +
>>> +int landlock_append_net_rule(struct landlock_ruleset *const ruleset, u16 port,
>>> +			     u32 access_hierarchy);
>>> +#else /* IS_ENABLED(CONFIG_INET) */
>>> +static inline void landlock_add_net_hooks(void)
>>> +{
>>> +}
>>> +#endif /* IS_ENABLED(CONFIG_INET) */
>>> +
>>> +#endif /* _SECURITY_LANDLOCK_NET_H */
>>> diff --git a/security/landlock/setup.c b/security/landlock/setup.c
>>> index f8e8e980454c..8059dc0b47d3 100644
>>> --- a/security/landlock/setup.c
>>> +++ b/security/landlock/setup.c
>>> @@ -14,6 +14,7 @@
>>>    #include "fs.h"
>>>    #include "ptrace.h"
>>>    #include "setup.h"
>>> +#include "net.h"
>>>
>>>    bool landlock_initialized __lsm_ro_after_init = false;
>>>
>>> @@ -28,6 +29,7 @@ static int __init landlock_init(void)
>>>    	landlock_add_cred_hooks();
>>>    	landlock_add_ptrace_hooks();
>>>    	landlock_add_fs_hooks();
>>> +	landlock_add_net_hooks();
>>>    	landlock_initialized = true;
>>>    	pr_info("Up and running.\n");
>>>    	return 0;
>>> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
>>> index 641155f6f6f8..16880e951346 100644
>>> --- a/security/landlock/syscalls.c
>>> +++ b/security/landlock/syscalls.c
>>> @@ -29,6 +29,7 @@
>>>    #include "cred.h"
>>>    #include "fs.h"
>>>    #include "limits.h"
>>> +#include "net.h"
>>>    #include "ruleset.h"
>>>    #include "setup.h"
>>>
>>> @@ -74,7 +75,8 @@ static void build_check_abi(void)
>>>    {
>>>    	struct landlock_ruleset_attr ruleset_attr;
>>>    	struct landlock_path_beneath_attr path_beneath_attr;
>>> -	size_t ruleset_size, path_beneath_size;
>>> +	struct landlock_net_service_attr net_service_attr;
>>> +	size_t ruleset_size, path_beneath_size, net_service_size;
>>>
>>>    	/*
>>>    	 * For each user space ABI structures, first checks that there is no
>>> @@ -90,6 +92,11 @@ static void build_check_abi(void)
>>>    	path_beneath_size += sizeof(path_beneath_attr.parent_fd);
>>>    	BUILD_BUG_ON(sizeof(path_beneath_attr) != path_beneath_size);
>>>    	BUILD_BUG_ON(sizeof(path_beneath_attr) != 12);
>>> +
>>> +	net_service_size = sizeof(net_service_attr.allowed_access);
>>> +	net_service_size += sizeof(net_service_attr.port);
>>> +	BUILD_BUG_ON(sizeof(net_service_attr) != net_service_size);
>>> +	BUILD_BUG_ON(sizeof(net_service_attr) != 10);
>>>    }
>>>
>>>    /* Ruleset handling */
>>> @@ -322,13 +329,54 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
>>>    	return err;
>>>    }
>>>
>>> +static int add_rule_net_service(struct landlock_ruleset *ruleset,
>>> +				const void __user *const rule_attr)
>>> +{
>>> +#if IS_ENABLED(CONFIG_INET)
>>> +	struct landlock_net_service_attr net_service_attr;
>>> +	int res;
>>> +	u32 mask;
>>> +
>>> +	/* Copies raw user space buffer, only one type for now. */
>>> +	res = copy_from_user(&net_service_attr, rule_attr,
>>> +			     sizeof(net_service_attr));
>>> +	if (res)
>>> +		return -EFAULT;
>>> +
>>> +	/*
>>> +	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
>>> +	 * are ignored by network actions.
>>> +	 */
>>> +	if (!net_service_attr.allowed_access)
>>> +		return -ENOMSG;
>>> +
>>> +	/*
>>> +	 * Checks that allowed_access matches the @ruleset constraints
>>> +	 * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
>>> +	 */
>>> +	mask = landlock_get_net_access_mask(ruleset, 0);
>>> +	if ((net_service_attr.allowed_access | mask) != mask)
>>> +		return -EINVAL;
>>> +
>>> +	/* Denies inserting a rule with port 0. */
>>> +	if (net_service_attr.port == 0)
>>> +		return -EINVAL;
>>> +
>>> +	/* Imports the new rule. */
>>> +	return landlock_append_net_rule(ruleset, net_service_attr.port,
>>> +					net_service_attr.allowed_access);
>>> +#else /* IS_ENABLED(CONFIG_INET) */
>>> +	return -EAFNOSUPPORT;
>>
>> I think this is the right approach to return -EAFNOSUPPORT here instead
>> of with landlock_create_ruleset() because if some network features are
>> not available this means that they will be denied. Only allowing some
>> exception (i.e. with a rule) would not make sense because it could work
>> at the end. This should be explained in the documentation.
>>
>> Landlock libraries would have to handle this error type as not-an-error
>> most of the time though, except when users want to be sure the running
>> system support such network feature.
>>
>> Any though?
> 
>     Yeah. I think the same - it's possible to create ruleset with network
> access attributes but if INET is not configured, it would be impossible
> to apply network rules and even try to call network syscalls
> corresponding applied attributes.
> 
>    Please could you explain more detailed about not-an-error handling logic?

It will depend on the best-effort level user space wants. Applications 
should already know by that time that there is no network support from 
the kernel.

Günther, what do you think about that?


>>
>>
>>> +#endif /* IS_ENABLED(CONFIG_INET) */
>>> +}
>>> +
>>>    /**
>>>     * sys_landlock_add_rule - Add a new rule to a ruleset
>>>     *
>>>     * @ruleset_fd: File descriptor tied to the ruleset that should be extended
>>>     *		with the new rule.
>>> - * @rule_type: Identify the structure type pointed to by @rule_attr (only
>>> - *             LANDLOCK_RULE_PATH_BENEATH for now).
>>> + * @rule_type: Identify the structure type pointed to by @rule_attr:
>>> + *             LANDLOCK_RULE_PATH_BENEATH or LANDLOCK_RULE_NET_SERVICE.
>>
>> %LANDLOCK_RULE_PATH_BENEATH or %LANDLOCK_RULE_NET_SERVICE.
>>
>     Got it.
>>
>>>     * @rule_attr: Pointer to a rule (only of type &struct
>>>     *             landlock_path_beneath_attr for now).
>>>     * @flags: Must be 0.
>>> @@ -339,6 +387,8 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
>>>     * Possible returned errors are:
>>>     *
>>>     * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
>>> + * - EAFNOSUPPORT: @rule_type is LANDLOCK_RULE_NET_SERVICE but TCP/IP is not
>>
>> %EAFNOSUPPORT
>> %LANDLOCK_RULE_NET_SERVICE
>>
>> BTW, I'll send a patch soon to fix some documentation style
>> inconsistency, including the missing "%" for defined values (e.g. errno).
>>
>    That would be great. Thanks.
>>
>>> + *   supported by the running kernel;
>>>     * - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
>>>     *   &landlock_path_beneath_attr.allowed_access is not a subset of the rule's
>>>     *   accesses);
>>> @@ -374,6 +424,9 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
>>>    	case LANDLOCK_RULE_PATH_BENEATH:
>>>    		err = add_rule_path_beneath(ruleset, rule_attr);
>>>    		break;
>>> +	case LANDLOCK_RULE_NET_SERVICE:
>>> +		err = add_rule_net_service(ruleset, rule_attr);
>>> +		break;
>>>    	default:
>>>    		err = -EINVAL;
>>>    		break;
>>> --
>>> 2.25.1
>>>
>> .