[PATCH v12 08/12] landlock: Add network rules and TCP hooks support

Mickaël Salaün mic at digikod.net
Tue Oct 10 09:28:09 UTC 2023


On Tue, Oct 10, 2023 at 06:29:56AM +0300, Konstantin Meskhidze (A) wrote:
> 
> 
> 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 at digikod.net>
> > > Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.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"
> 
>    Ok. Thanks.
> > 
> > 
> > > 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.
> 
>   Ok. Got it.
> > 
> > > +	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).
> > 
>  Do I have to ignore it according your next mail thread:
>  https://lore.kernel.org/netdev/20231009.meet7uTaeghu@digikod.net/
> ????

Yes please ignore this part, the latest mail prevails. This should be a
static function.

> > > +{
> > > +	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.
> > 
>   Should I still update prefix according your suggestions (keep
> add_rule_net_service() in syscalls.c) in the next mail thread or keep it as
> it is:
>   https://lore.kernel.org/netdev/20231009.meet7uTaeghu@digikod.net/
> ????

No, the prefix notation is only useful for exported functions, just
renamed it to add_rule_net_port() and make it static.

> > 
> > > +			 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().

Same as above, this is not relevant anymore.

> > 
> > > +	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.
> > 
> > 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.
> 
>   So like I understand refactoring will be like this:
> 	1. Allow bind for zero port.
> 	2. Update tests:
> 		- add rule with port 0;
> 		- bind "random" port;
> 		- using getsockname to get binded port;
> 		- connect to the socket using binded port;
> 		
>  Correct??

Yes. You can also extend this test to try binding to a lower port (e.g.
1024, value of srv0.port), not part of ip_local_port_range, which should
then be denied.

> > 
> > > +	    (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".
> 
>   Ok. thanks.
> > 
> > 
> > > 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
> 
>   right. will be fixed.
> > .



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