Message-ID: <ad7d294e-267c-d233-e8d6-c92108f229d8@huawei.com>
Date: Wed, 11 Oct 2023 04:53:57 +0300
From: "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>
To: Mickaël Salaün <mic@...ikod.net>
CC: <willemdebruijn.kernel@...il.com>, <gnoack3000@...il.com>,
	<linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
	<netfilter-devel@...r.kernel.org>, <yusongping@...wei.com>,
	<artem.kuzin@...wei.com>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v12 08/12] landlock: Add network rules and TCP hooks
 support



10/2/2023 11:26 PM, Mickaël Salaün пишет:
> Thanks for this new version Konstantin. I pushed this series, with minor
> changes, to -next. So far, no warning. But it needs some changes, mostly
> kernel-only, but also one with the handling of port 0 with bind (see my
> review below).
> 
> On Wed, Sep 20, 2023 at 05:26:36PM +0800, 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 enables to restrict TCP socket binding and connection
>> to specific ports.
>> The new landlock_net_port_attr structure has two fields. The allowed_access
>> field contains the LANDLOCK_ACCESS_NET_* rights. The port field contains
>> the port value according to the allowed protocol. This field can
>> take up to a 64-bit value [1] but the maximum value depends on the related
>> protocol (e.g. 16-bit for TCP).
>> 
>> [1]
>> https://lore.kernel.org/r/278ab07f-7583-a4e0-3d37-1bacd091531d@digikod.net
>> 
>> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
>> ---
>> 
>> Changes since v11:
>> * Replace dates with "2022-2023" in net.c/h files headers.
>> * Removes WARN_ON_ONCE(!domain) in check_socket_access().
>> * Using "typeof(*address)" instead of offsetofend(struct sockaddr, sa_family).
>> * Renames LANDLOCK_RULE_NET_SERVICE to LANDLOCK_RULE_NET_PORT.
>> * Renames landlock_net_service_attr to landlock_net_port_attr.
>> * Defines two add_rule_net_service() functions according to
>>   IS_ENABLED(CONFIG_INET) instead of changing the body of the only
>>   function.
>> * Adds af_family consistency check while handling AF_UNSPEC specifically.
>> * Adds bind_access_mask in add_rule_net_service() to deny all rules with bind
>>   action on port zero.
>> * Minor fixes.
>> * Refactors commit message.
>> 
>> Changes since v10:
>> * Removes "packed" attribute.
>> * Applies Mickaёl's patch with some refactoring.
>> * Deletes get_port() and check_addrlen() helpers.
>> * Refactors check_socket_access() by squashing get_port() and
>>   check_addrlen() helpers into it.
>> * Fixes commit message.
>> 
>> Changes since v9:
>> * Changes UAPI port field to __u64.
>> * Moves shared code into check_socket_access().
>> * Adds get_raw_handled_net_accesses() and
>>   get_current_net_domain() helpers.
>> * Minor fixes.
>> 
>> 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                |  47 ++++
>>  security/landlock/Kconfig                    |   3 +-
>>  security/landlock/Makefile                   |   2 +
>>  security/landlock/limits.h                   |   5 +
>>  security/landlock/net.c                      | 241 +++++++++++++++++++
>>  security/landlock/net.h                      |  35 +++
>>  security/landlock/ruleset.c                  |  62 ++++-
>>  security/landlock/ruleset.h                  |  59 ++++-
>>  security/landlock/setup.c                    |   2 +
>>  security/landlock/syscalls.c                 |  33 ++-
>>  tools/testing/selftests/landlock/base_test.c |   2 +-
>>  11 files changed, 467 insertions(+), 24 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 81d09ef9aa50..3b8400e8a4d9 100644
>> --- a/include/uapi/linux/landlock.h
>> +++ b/include/uapi/linux/landlock.h
>> @@ -31,6 +31,12 @@ 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 +60,11 @@ enum landlock_rule_type {
>>  	 * landlock_path_beneath_attr .
>>  	 */
>>  	LANDLOCK_RULE_PATH_BENEATH = 1,
>> +	/**
>> +	 * @LANDLOCK_RULE_NET_PORT: Type of a &struct
>> +	 * landlock_net_port_attr .
>> +	 */
>> +	LANDLOCK_RULE_NET_PORT = 2,
>>  };
>> 
>>  /**
>> @@ -79,6 +90,23 @@ struct landlock_path_beneath_attr {
>>  	 */
>>  } __attribute__((packed));
>> 
>> +/**
>> + * struct landlock_net_port_attr - Network service definition
> 
> "Network port definition"
> 
> 
>> diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
>> index c1e862a38410..10c099097533 100644
>> --- a/security/landlock/Kconfig
>> +++ b/security/landlock/Kconfig
>> @@ -2,7 +2,8 @@
>> 
>>  config SECURITY_LANDLOCK
>>  	bool "Landlock support"
>> -	depends on SECURITY
>> +	depends on SECURITY && !ARCH_EPHEMERAL_INODES
> 
> !ARCH_EPHEMERAL_INODES is definitely gone now.
> 
>> +	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..93c9c6f91556 100644
>> --- a/security/landlock/limits.h
>> +++ b/security/landlock/limits.h
>> @@ -23,6 +23,11 @@
>>  #define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
>>  #define LANDLOCK_SHIFT_ACCESS_FS	0
>> 
>> +#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..62b830653e25
>> --- /dev/null
>> +++ b/security/landlock/net.c
>> @@ -0,0 +1,241 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Landlock LSM - Network management and hooks
>> + *
>> + * Copyright © 2022-2023 Huawei Tech. Co., Ltd.
>> + * Copyright © 2022-2023 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)
> 
> This function is only used in add_rule_net_service(), so it should not
> be exported, and we can merge it (into landlock_add_rule_net_port).
> 
>> +{
>> +	int err;
>> +	const struct landlock_id id = {
>> +		.key.data = (__force uintptr_t)htons(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;
>> +}
>> +
>> +int add_rule_net_service(struct landlock_ruleset *ruleset,
> 
> We should only export functions with a "landlock_" prefix, and "service"
> is now replaced with "port", which gives landlock_add_rule_net_port().
> 
> For consistency, we should also rename add_rule_path_beneath() into
> landlock_add_rule_path_beneath(), move it into fs.c, and merge
> landlock_append_fs_rule() into it (being careful to not move the related
> code to ease review). This change should be part of the "landlock:
> Refactor landlock_add_rule() syscall" patch. Please be careful to keep
> the other changes happening in other patches.
> 
> 
>> +			 const void __user *const rule_attr)
>> +{
>> +	struct landlock_net_port_attr net_port_attr;
>> +	int res;
>> +	access_mask_t mask, bind_access_mask;
>> +
>> +	/* Copies raw user space buffer. */
>> +	res = copy_from_user(&net_port_attr, rule_attr, sizeof(net_port_attr));
> 
> We should include <linux/uaccess.h> because of copy_from_user().
> 
> Same for landlock_add_rule_path_beneath().
> 
>> +	if (res)
>> +		return -EFAULT;
>> +
>> +	/*
>> +	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
>> +	 * are ignored by network actions.
>> +	 */
>> +	if (!net_port_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_port_attr.allowed_access | mask) != mask)
>> +		return -EINVAL;
>> +
>> +	/*
>> +	 * Denies inserting a rule with port 0 (for bind action) or
>> +	 * higher than 65535.
>> +	 */
>> +	bind_access_mask = net_port_attr.allowed_access &
>> +			   LANDLOCK_ACCESS_NET_BIND_TCP;
>> +	if (((net_port_attr.port == 0) &&
>> +	     (bind_access_mask == LANDLOCK_ACCESS_NET_BIND_TCP)) ||
> 
> For context about "port 0 binding" see
> https://lore.kernel.org/all/7cb458f1-7aff-ccf3-abfd-b563bfc65b84@huawei.com/
> 
> I previously said:
>>> > To say it another way, we should not allow to add a rule with port
>>> > 0 for
>>> > LANDLOCK_ACCESS_NET_BIND_TCP, but return -EINVAL in this case. This
>>> > limitation should be explained, documented and tested.
> 
> Thinking more about this port 0 for bind (and after an interesting
> discussion with Eric), it would be a mistake to forbid a rule to bind on
> port 0 because this is very useful for some network services, and
> because it would not be reasonable to have an LSM hook to control such
> "random ports". Instead we should document what using this value means
> (i.e. pick a dynamic available port in a range defined by the sysadmin)
> and highlight the fact that it is controlled with the
> /proc/sys/net/ipv4/ip_local_port_range sysctl, which is also used by
> IPv6.

   Hi Mickaёl.
   I also wonder which part of documentation (landlock.rst) we should 
include zero port description in?
> 
> We then need to test binding on port zero by getting the binded port
> (cf. getsockopt/getsockname) and checking that we can indeed connect to
> it.
> 
>> +	    (net_port_attr.port > U16_MAX))
>> +		return -EINVAL;
>> +
>> +	/* Imports the new rule. */
>> +	return landlock_append_net_rule(ruleset, net_port_attr.port,
>> +					net_port_attr.allowed_access);
>> +}
> 
>> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
>> index 1ede2b9a79b7..9bd0483c64d4 100644
>> --- a/security/landlock/ruleset.h
>> +++ b/security/landlock/ruleset.h
>> @@ -33,13 +33,16 @@
>>  typedef u16 access_mask_t;
>>  /* Makes sure all filesystem access rights can be stored. */
>>  static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
>> +/* Makes sure all network access rights can be stored. */
>> +static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET);
>>  /* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
>>  static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
>> 
>>  /* Ruleset access masks. */
>> -typedef u16 access_masks_t;
>> +typedef u32 access_masks_t;
>>  /* Makes sure all ruleset access rights can be stored. */
>> -static_assert(BITS_PER_TYPE(access_masks_t) >= LANDLOCK_NUM_ACCESS_FS);
>> +static_assert(BITS_PER_TYPE(access_masks_t) >=
>> +	      LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET);
>> 
>>  typedef u16 layer_mask_t;
>>  /* Makes sure all layers can be checked. */
>> @@ -84,6 +87,11 @@ enum landlock_key_type {
>>  	 * keys.
>>  	 */
>>  	LANDLOCK_KEY_INODE = 1,
>> +	/**
>> +	 * @LANDLOCK_KEY_NET_PORT: Type of &landlock_ruleset.root_net_port's
>> +	 * node keys.
>> +	 */
>> +	LANDLOCK_KEY_NET_PORT = 2,
> 
> You don't need to specify "2".
> 
> 
>> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
>> index 8a54e87dbb17..da6cbd0032ca 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_port_attr net_port_attr;
>> +	size_t ruleset_size, path_beneath_size, net_service_size;
> 
> net_port_size
> .

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