Message-ID: <71dd7517-4d3c-b644-18bd-cb792d68bcd8@digikod.net>
Date:   Tue, 6 Sep 2022 10:08:57 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
        gnoack3000@...il.com
Cc:     willemdebruijn.kernel@...il.com,
        linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, yusongping@...wei.com,
        hukeping@...wei.com, anton.sirazetdinov@...wei.com
Subject: Re: [PATCH v7 09/18] landlock: implement TCP network hooks


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.


> could support network confinement.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.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"

> +#include "cred.h"
> +#include "limits.h"
> +#include "net.h"

#include "ruleset.h"

> +
> +int landlock_append_net_rule(struct landlock_ruleset *const ruleset, u16 port,
> +			     u32 access_rights)

Please constify all arguments, in this function and others.

> +{
> +	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

> +		/*
> +		 * 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?


> +#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.


>    * @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).


> + *   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
> 

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