[PATCH v5 08/15] landlock: TCP network hooks implementation
Konstantin Meskhidze
konstantin.meskhidze at huawei.com
Thu May 19 11:40:42 UTC 2022
5/17/2022 11:51 AM, Mickaël Salaün пишет:
>
> On 16/05/2022 17:20, Konstantin Meskhidze wrote:
>> Support of socket_bind() and socket_connect() hooks.
>> Its possible to restrict binding and connecting of TCP
>> types of sockets to particular ports. Its just basic idea
>> how Landlock could support network confinement.
>>
>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.com>
>> ---
>>
>> Changes since v3:
>> * Split commit.
>> * Add SECURITY_NETWORK in config.
>> * Add IS_ENABLED(CONFIG_INET) if a kernel has no INET configuration.
>> * Add hook_socket_bind and hook_socket_connect hooks.
>>
>> Changes since v4:
>> * Factors out CONFIG_INET into make file.
>> * Refactoring 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.
>> * Refactoring add_rule_net_service() and landlock_add_rule
>> syscall to support network rule inserting.
>> * Refactoring init_layer_masks() to support network rules.
>>
>> ---
>> security/landlock/Kconfig | 1 +
>> security/landlock/Makefile | 2 +
>> security/landlock/net.c | 159 +++++++++++++++++++++++++++++++++++
>> security/landlock/net.h | 25 ++++++
>> security/landlock/ruleset.c | 15 +++-
>> security/landlock/setup.c | 2 +
>> security/landlock/syscalls.c | 63 ++++++++++++--
>> 7 files changed, 261 insertions(+), 6 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..9302e5891991
>> --- /dev/null
>> +++ b/security/landlock/net.c
>> @@ -0,0 +1,159 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Landlock LSM - Network management and hooks
>> + *
>> + * Copyright (C) 2022 Huawei Tech. Co., Ltd.
>> + */
>> +
>> +#include <linux/in.h>
>> +#include <linux/net.h>
>> +#include <linux/socket.h>
>> +#include <net/ipv6.h>
>> +
>> +#include "cred.h"
>> +#include "limits.h"
>> +#include "net.h"
>> +
>> +int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
>> + u16 port, u32 access_rights)
>> +{
>> + int err;
>> +
>> + /* Transforms relative access rights to absolute ones. */
>> + access_rights |= LANDLOCK_MASK_ACCESS_NET &
>> + ~landlock_get_net_access_mask(ruleset, 0);
>> +
>> + BUILD_BUG_ON(sizeof(port) > sizeof(uintptr_t));
>> + mutex_lock(&ruleset->lock);
>> + err = landlock_insert_rule(ruleset, NULL, port,
>> + access_rights, LANDLOCK_RULE_NET_SERVICE);
>> + 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;
>> +
>> + if (WARN_ON_ONCE(!domain))
>> + return 0;
>> + if (WARN_ON_ONCE(domain->num_layers < 1))
>> + return -EACCES;
>> +
>> + rule = landlock_find_rule(domain, port,
>> + LANDLOCK_RULE_NET_SERVICE);
>> +
>> + handled_access = init_layer_masks(domain, access_request,
>> + &layer_masks, sizeof(layer_masks),
>> + LANDLOCK_RULE_NET_SERVICE);
>> + 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:
>
> Are you sure about that?
>
> Please write a test for this case.
>
I checked the logic in Selinux LSM in a bind() hook and AF_UNSPEC
family is treated as AF_INET (only for INADDR_ANY address) but we can
discuss it.
>
>> + case AF_INET:
>> + {
>
> You don't need these braces (except if it is required by checkpatch.pl).
>
I got compilation error without braces:
...
error: a label can only be part of a statement and a declaration is not
a statement
67 | const struct sockaddr_in *const sockaddr =
...
so I added braces.
>
>> + 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
>> + }
>
> You missed some part of my patch… We should not get the port for a
> protocol we don't know, hence the WARN_ON_ONCE.
>
Sorry. I manually updated the code and missed that. I will fix it.
>
>> + 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;
>> +
>> + /* Get port value in host byte order */
>
> I moved/removed this in my patch against v4 for a reason. Please, ask if
> you don't understand or if you don't agree with something I said.
>
Sorry. I updated your changed manually and missed that.
Will be fixed.
>
>> + switch (address->sa_family) {
>> + case AF_UNSPEC:
>
> Is this correct?
Actually I did'not find any issue with bind() using AF_UNSPEC family.
(instead of connect() one and we came to an agreement that it must be
banned). So I checked athoner LSMs like Selinux and found out that
it treats bind() hook with AF_UNSPEC family as with AF_INET one.
But Selinux allows AF_UNSPEC family only for INADDR_ANY address and
I cant understand the reason now. So I let AF_UNSPEC family bind()
hook for any address, but we can discuss it. What do you think?
>
> Please write a test for this case.
>
I have one. Please check it in connect_afunspec_with_restictions
test:
...
/* Enforces the ruleset. */
enforce_ruleset(_metadata, ruleset_fd_1);
/* Creates a server socket 1 */
sockfd = create_socket(_metadata, false, false);
ASSERT_LE(0, sockfd);
/* Binds the socket 1 to address with port[0] with AF_UNSPEC
family */
self->addr4[0].sin_family = AF_UNSPEC;
ASSERT_EQ(0, bind(sockfd, (struct sockaddr *)&self->addr4[0],
sizeof(self->addr4[0])));
/* Makes connection to socket with port[0] */
ASSERT_EQ(0, connect(sockfd, (struct sockaddr *)&self->addr4[0],
sizeof(self->addr4[0])));
const int ruleset_fd_2 =
landlock_create_ruleset(&ruleset_attr_2,
sizeof(ruleset_attr_2), 0);
ASSERT_LE(0, ruleset_fd_2);
/* Allows connect and bind operations to the port[0] socket */
ASSERT_EQ(0, landlock_add_rule(ruleset_fd_2,
LANDLOCK_RULE_NET_SERVICE,
&net_service_2, 0));
...
>> + 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;
>> +
>> + /* Get port value in host byte order */
>> + 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;
>> + /*
>> + * 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..da5ce8fa04cc
>> --- /dev/null
>> +++ b/security/landlock/net.h
>> @@ -0,0 +1,25 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Landlock LSM - Network management and hooks
>> + *
>> + * Copyright (C) 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/ruleset.c b/security/landlock/ruleset.c
>> index ea9ecb3f471a..317cf98890f6 100644
>> --- a/security/landlock/ruleset.c
>> +++ b/security/landlock/ruleset.c
>> @@ -671,7 +671,7 @@ access_mask_t get_handled_accesses(
>> }
>> break;
>> default:
>> - break;
>> + return 0;
>
> Why?
You are right - this is useless code, cause anyway 0 is retured in
default rule_type. Will be fixed.
>
>
>> }
>> return access_dom;
>> }
>> @@ -763,6 +763,19 @@ access_mask_t init_layer_masks(const struct
>> landlock_ruleset *const domain,
>> }
>> }
>> break;
>> + case LANDLOCK_RULE_NET_SERVICE:
>> + for_each_set_bit(access_bit, &access_req,
>> + LANDLOCK_NUM_ACCESS_NET) {
>> + if (landlock_get_net_access_mask(domain,
>> + layer_level) &
>> + BIT_ULL(access_bit)) {
>> + (*layer_masks)[access_bit] |=
>> + BIT_ULL(layer_level);
>> + handled_accesses |=
>> + BIT_ULL(access_bit);
>> + }
>> + }
>> + break;
>> default:
>> return 0;
>> }
>> 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 812541f4e155..9454c6361011 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 */
>> @@ -299,9 +306,9 @@ static int add_rule_path_beneath(struct
>> landlock_ruleset *const ruleset,
>> * Informs about useless rule: empty allowed_access (i.e. deny
>> rules)
>> * are ignored in path walks.
>> */
>> - if (!path_beneath_attr.allowed_access) {
>> + if (!path_beneath_attr.allowed_access)
>
> Why?
Unnecessary braces for single statement blocks.
I got a warning by scripts/checkpatch.pl:
WARNING: braces {} are not necessary for single statement blocks
#309: FILE: security/landlock/syscalls.c:309:
+ if (!path_beneath_attr.allowed_access) {
+ return -ENOMSG;
+ }
>
>
>> return -ENOMSG;
>> - }
>> +
>> /*
>> * Checks that allowed_access matches the @ruleset constraints
>> * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
>> @@ -323,13 +330,54 @@ 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 *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;
>> +#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.
>> * @rule_attr: Pointer to a rule (only of type &struct
>> * landlock_path_beneath_attr for now).
>> * @flags: Must be 0.
>> @@ -340,6 +388,8 @@ 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
>> + * 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);
>> @@ -375,6 +425,9 @@ SYSCALL_DEFINE4(landlock_add_rule,
>> 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
>>
> .
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