[PATCH v9 08/12] landlock: Add network rules and TCP hooks support
Konstantin Meskhidze (A)
konstantin.meskhidze at huawei.com
Mon Mar 6 10:18:40 UTC 2023
2/21/2023 9:04 PM, Mickaël Salaün пишет:
>
>
> 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.
>
Ok. I got it.
>
>> +}
>> +
>> +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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