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Message-ID: <ae75cb3c-2b08-2260-041a-36ee643996ad@digikod.net>
Date: Mon, 9 Jan 2023 13:38:48 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>,
netdev@...r.kernel.org, linux-api@...r.kernel.org,
"Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
Cc: willemdebruijn.kernel@...il.com, gnoack3000@...il.com,
linux-security-module@...r.kernel.org,
netfilter-devel@...r.kernel.org, artem.kuzin@...wei.com
Subject: Re: [PATCH v8 08/12] landlock: Implement TCP network hooks
On 09/01/2023 09:07, Konstantin Meskhidze (A) wrote:
>
>
> 1/6/2023 10:30 PM, Mickaël Salaün пишет:
>>
>> On 05/01/2023 09:57, Konstantin Meskhidze (A) wrote:
>>>
>>>
>>> 11/17/2022 9:43 PM, Mickaël Salaün пишет:
>>>>
>>>> On 21/10/2022 17:26, Konstantin Meskhidze wrote:
>>>>> This patch adds support of socket_bind() and socket_connect() hooks.
>>>>> It's possible to restrict binding and connecting of TCP sockets to
>>>>> particular ports.
>>>>
>>>> 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@...wei.com>
>>>>> ---
>>>>>
>>>>> Changes since v7:
>>>>> * Minor fixes.
>>>>> * Refactors commit message.
>>>>>
>>>>> 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 | 164 +++++++++++++++++++++++++++++++++++
>>>>> security/landlock/net.h | 26 ++++++
>>>>> security/landlock/setup.c | 2 +
>>>>> security/landlock/syscalls.c | 59 ++++++++++++-
>>>>> 6 files changed, 251 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..39e8a156a1f4
>>>>> --- /dev/null
>>>>> +++ b/security/landlock/net.c
>>>>> @@ -0,0 +1,164 @@
>>>>> +// 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 u16 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_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)
>>>>
>>>> get_port() should return a __be16 type. This enables to avoid converting
>>>> port when checking a rule.
>>>
>>> In this case a user must do a coverting port into __be16:
>>>
>>> struct landlock_net_service_attr net_service = {
>>> .allowed_access = LANDLOCK_ACCESS_NET_BIND_TCP,
>>>
>>> .port = htons(sock_port),
>>> };
>>> I think that a user should not think about this conversion cause it
>>> makes UAPI more complex to use. Lets do this under kernel's hood and let
>>> it as it is now -> u16 port.
>>>
>>> What do you think?
>>
>> BE and LE conversions may be error prone without strong typing, but the
>> current Linux network UAPI uses this convention (see related syscalls),
>> so developers already use htons() in their applications. I think it is
>> less hazardous to use the same convention. It would be nice to have the
>> point of view of network and API folks though.
>
> Ok. Thanks. Let ports be in BE format like in network packets.
>
> What should a selftest with port conversion be like?
>
> 1. Set a port with a Landlock rule with no conversion. get an error
> wit bind/connect actions.
> 2. Convert a port with htons(sock_port). get no error.
>
> What do you think?
Right, you can do both on a LE architecture (that must be checked in the
test or it should be skipped), test with a port value that has different
representation in LE and BE.
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