Re: [PATCH v8 08/12] landlock: Implement TCP network hooks

["Konstantin Meskhidze (A)" <konstantin.meskhidze@huawei.com>]

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@huawei.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?


> 
> make C=2 security/landlock/ must not print any warning.
> 
> 
>> +{
>> +	/* 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;
> 
> You can remove this default case and move the return 0 at the end of the
> function.
> 
> 
>> +	}
>> +}
>> +
>> +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;
> 
> You can move "i" after the "dom" declaration to remove the extra braces.
> 
> 
>> +
>> +		/*
>> +		 * 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;
> 
> I'm wondering if this is the right error code for this case. EPERM may
> be more appropriate.
> 
> Thinking more about this case, I don't understand what is the rationale
> to deny such action. What would be the consequence to always allow
> connection with AF_UNSPEC (i.e. to disconnect a socket)?
> 
> 
>> +		}
>> +	}
>> +	}
>> +	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..0da1d9dff5ab
>> --- /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,
>> +			     const u16 port, access_mask_t access_rights);
>> +#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 3f196d2ce4f9..7e4a598177b8 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;
>> 
>> @@ -29,6 +30,7 @@ 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 c5a6ad4e2fca..7853f32e8325 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;
> 
> access_mask_t 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.
>> @@ -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
> 
> %LANDLOCK_RULE_NET_SERVICE
> 
> 
>> + *   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
>>    *   ruleset handled accesses);
>> @@ -373,6 +423,9 @@ 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
>> 
> .