Re: [PATCH v9 08/12] landlock: Add network rules and TCP hooks support

["Mickaël Salaün" <mic@digikod.net>]

On 16/01/2023 09:58, 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 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                      | 200 +++++++++++++++++++
>   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, 452 insertions(+), 23 deletions(-)
>   create mode 100644 security/landlock/net.c
>   create mode 100644 security/landlock/net.h
> 
> diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
> index f3223f964691..ae11c663c975 100644
> --- a/include/uapi/linux/landlock.h
> +++ b/include/uapi/linux/landlock.h
> @@ -31,6 +31,13 @@ struct landlock_ruleset_attr {
>   	 * this access right.
>   	 */
>   	__u64 handled_access_fs;
> +
> +	/**
> +	 * @handled_access_net: Bitmask of actions (cf. `Network flags`_)
> +	 * that is handled by this ruleset and should then be forbidden if no
> +	 * rule explicitly allow them.
> +	 */
> +	__u64 handled_access_net;
>   };
>   
>   /*
> @@ -54,6 +61,11 @@ enum landlock_rule_type {
>   	 * landlock_path_beneath_attr .
>   	 */
>   	LANDLOCK_RULE_PATH_BENEATH = 1,
> +	/**
> +	 * @LANDLOCK_RULE_NET_SERVICE: Type of a &struct
> +	 * landlock_net_service_attr .
> +	 */
> +	LANDLOCK_RULE_NET_SERVICE = 2,
>   };
>   
>   /**
> @@ -79,6 +91,24 @@ struct landlock_path_beneath_attr {
>   	 */
>   } __attribute__((packed));
>   
> +/**
> + * struct landlock_net_service_attr - TCP subnet definition
> + *
> + * Argument of sys_landlock_add_rule().
> + */
> +struct landlock_net_service_attr {
> +	/**
> +	 * @allowed_access: Bitmask of allowed access network for services
> +	 * (cf. `Network flags`_).
> +	 */
> +	__u64 allowed_access;
> +	/**
> +	 * @port: Network port.
> +	 */
> +	__be16 port;
> +
> +} __attribute__((packed));
> +
>   /**
>    * DOC: fs_access
>    *
> @@ -173,4 +203,23 @@ struct landlock_path_beneath_attr {
>   #define LANDLOCK_ACCESS_FS_TRUNCATE			(1ULL << 14)
>   /* clang-format on */
>   
> +/**
> + * DOC: net_access
> + *
> + * Network flags
> + * ~~~~~~~~~~~~~~~~
> + *
> + * These flags enable to restrict a sandboxed process to a set of network
> + * actions.
> + *
> + * TCP sockets with allowed actions:
> + *
> + * - %LANDLOCK_ACCESS_NET_BIND_TCP: Bind a TCP socket to a local port.
> + * - %LANDLOCK_ACCESS_NET_CONNECT_TCP: Connect an active TCP socket to
> + *   a remote port.
> + */
> +/* clang-format off */
> +#define LANDLOCK_ACCESS_NET_BIND_TCP			(1ULL << 0)
> +#define LANDLOCK_ACCESS_NET_CONNECT_TCP			(1ULL << 1)
> +/* clang-format on */
>   #endif /* _UAPI_LINUX_LANDLOCK_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/limits.h b/security/landlock/limits.h
> index bafb3b8dc677..8a1a6463c64e 100644
> --- a/security/landlock/limits.h
> +++ b/security/landlock/limits.h
> @@ -23,6 +23,10 @@
>   #define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
>   #define LANDLOCK_SHIFT_ACCESS_FS	0
>   
> -/* clang-format on */
> +#define LANDLOCK_LAST_ACCESS_NET	LANDLOCK_ACCESS_NET_CONNECT_TCP
> +#define LANDLOCK_MASK_ACCESS_NET	((LANDLOCK_LAST_ACCESS_NET << 1) - 1)
> +#define LANDLOCK_NUM_ACCESS_NET		__const_hweight64(LANDLOCK_MASK_ACCESS_NET)
> +#define LANDLOCK_SHIFT_ACCESS_NET	LANDLOCK_NUM_ACCESS_FS
>   
> +/* clang-format on */
>   #endif /* _SECURITY_LANDLOCK_LIMITS_H */
> diff --git a/security/landlock/net.c b/security/landlock/net.c
> new file mode 100644
> index 000000000000..338bd6dd8e3f
> --- /dev/null
> +++ b/security/landlock/net.c
> @@ -0,0 +1,200 @@
> +// 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,
> +			     const __be16 port, access_mask_t access_rights)
> +{
> +	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_addrlen(const struct sockaddr *const address, int addrlen)
> +{
> +	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 int check_socket_access(const struct landlock_ruleset *const domain,
> +			       struct sockaddr *address, __be16 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;
> +
> +	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));
> +
> +		fallthrough;
> +	}
> +	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 sockaddr->sin_port;
> +	}
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case AF_INET6: {
> +		const struct sockaddr_in6 *const sockaddr_ip6 =
> +			(struct sockaddr_in6 *)address;
> +		return sockaddr_ip6->sin6_port;
> +	}
> +#endif
> +	}
> +	WARN_ON_ONCE(1);
> +	return 0;
> +}
> +
> +static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
> +			    int addrlen)
> +{
> +	int ret;
> +	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;
> +
> +	ret = check_addrlen(address, addrlen);
> +	if (ret)
> +		return ret;
> +
> +	return check_socket_access(dom, address, get_port(address),
> +				   LANDLOCK_ACCESS_NET_BIND_TCP);

Both hook_socket_bind() and hook_socket_connect() looks the same except 
the access right. All this code could be moved to check_socket_access(). 
get_port() would need to be defined before.


> +}
> +
> +static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
> +			       int addrlen)
> +{
> +	int ret;
> +	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;
> +
> +	ret = check_addrlen(address, addrlen);
> +	if (ret)
> +		return ret;
> +
> +	return check_socket_access(dom, address, get_port(address),
> +				   LANDLOCK_ACCESS_NET_CONNECT_TCP);
> +}