[PATCH v7 09/18] landlock: implement TCP network hooks
Mickaël Salaün
mic at digikod.net
Tue Sep 6 08:08:57 UTC 2022
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 at 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"
> +#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
>
More information about the Linux-security-module-archive
mailing list