[PATCH v9 08/12] landlock: Add network rules and TCP hooks support
Mickaël Salaün
mic at digikod.net
Tue Feb 21 18:04:44 UTC 2023
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 at 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);
> +}
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