landlock: Add ruleset and domain management (0b9c666e) · Commits · EulixOS / Software / Kernel

security/landlock/Makefile

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		obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

		landlock-y := object.o
		landlock-y := object.o ruleset.o

security/landlock/limits.h

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		/* SPDX-License-Identifier: GPL-2.0-only */
		/*
		* Landlock LSM - Limits for different components
		*
		* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
		* Copyright © 2018-2020 ANSSI
		*/

		#ifndef _SECURITY_LANDLOCK_LIMITS_H
		#define _SECURITY_LANDLOCK_LIMITS_H

		#include <linux/limits.h>

		#define LANDLOCK_MAX_NUM_LAYERS 64
		#define LANDLOCK_MAX_NUM_RULES U32_MAX

		#endif /* _SECURITY_LANDLOCK_LIMITS_H */

security/landlock/ruleset.c

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		// SPDX-License-Identifier: GPL-2.0-only
		/*
		* Landlock LSM - Ruleset management
		*
		* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
		* Copyright © 2018-2020 ANSSI
		*/

		#include <linux/bits.h>
		#include <linux/bug.h>
		#include <linux/compiler_types.h>
		#include <linux/err.h>
		#include <linux/errno.h>
		#include <linux/kernel.h>
		#include <linux/lockdep.h>
		#include <linux/overflow.h>
		#include <linux/rbtree.h>
		#include <linux/refcount.h>
		#include <linux/slab.h>
		#include <linux/spinlock.h>
		#include <linux/workqueue.h>

		#include "limits.h"
		#include "object.h"
		#include "ruleset.h"

		static struct landlock_ruleset *create_ruleset(const u32 num_layers)
		{
		struct landlock_ruleset *new_ruleset;

		new_ruleset = kzalloc(struct_size(new_ruleset, fs_access_masks,
		num_layers), GFP_KERNEL_ACCOUNT);
		if (!new_ruleset)
		return ERR_PTR(-ENOMEM);
		refcount_set(&new_ruleset->usage, 1);
		mutex_init(&new_ruleset->lock);
		new_ruleset->root = RB_ROOT;
		new_ruleset->num_layers = num_layers;
		/*
		* hierarchy = NULL
		* num_rules = 0
		* fs_access_masks[] = 0
		*/
		return new_ruleset;
		}

		struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask)
		{
		struct landlock_ruleset *new_ruleset;

		/* Informs about useless ruleset. */
		if (!fs_access_mask)
		return ERR_PTR(-ENOMSG);
		new_ruleset = create_ruleset(1);
		if (!IS_ERR(new_ruleset))
		new_ruleset->fs_access_masks[0] = fs_access_mask;
		return new_ruleset;
		}

		static void build_check_rule(void)
		{
		const struct landlock_rule rule = {
		.num_layers = ~0,
		};

		BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
		}

		static struct landlock_rule *create_rule(
		struct landlock_object *const object,
		const struct landlock_layer (*const layers)[],
		const u32 num_layers,
		const struct landlock_layer *const new_layer)
		{
		struct landlock_rule *new_rule;
		u32 new_num_layers;

		build_check_rule();
		if (new_layer) {
		/* Should already be checked by landlock_merge_ruleset(). */
		if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
		return ERR_PTR(-E2BIG);
		new_num_layers = num_layers + 1;
		} else {
		new_num_layers = num_layers;
		}
		new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
		GFP_KERNEL_ACCOUNT);
		if (!new_rule)
		return ERR_PTR(-ENOMEM);
		RB_CLEAR_NODE(&new_rule->node);
		landlock_get_object(object);
		new_rule->object = object;
		new_rule->num_layers = new_num_layers;
		/* Copies the original layer stack. */
		memcpy(new_rule->layers, layers,
		flex_array_size(new_rule, layers, num_layers));
		if (new_layer)
		/* Adds a copy of @new_layer on the layer stack. */
		new_rule->layers[new_rule->num_layers - 1] = *new_layer;
		return new_rule;
		}

		static void free_rule(struct landlock_rule *const rule)
		{
		might_sleep();
		if (!rule)
		return;
		landlock_put_object(rule->object);
		kfree(rule);
		}

		static void build_check_ruleset(void)
		{
		const struct landlock_ruleset ruleset = {
		.num_rules = ~0,
		.num_layers = ~0,
		};

		BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
		BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
		}

		/**
		* insert_rule - Create and insert a rule in a ruleset
		*
		* @ruleset: The ruleset to be updated.
		* @object: The object to build the new rule with. The underlying kernel
		* object must be held by the caller.
		* @layers: One or multiple layers to be copied into the new rule.
		* @num_layers: The number of @layers entries.
		*
		* When user space requests to add a new rule to a ruleset, @layers only
		* contains one entry and this entry is not assigned to any level. In this
		* case, the new rule will extend @ruleset, similarly to a boolean OR between
		* access rights.
		*
		* When merging a ruleset in a domain, or copying a domain, @layers will be
		* added to @ruleset as new constraints, similarly to a boolean AND between
		* access rights.
		*/
		static int insert_rule(struct landlock_ruleset *const ruleset,
		struct landlock_object *const object,
		const struct landlock_layer (*const layers)[],
		size_t num_layers)
		{
		struct rb_node **walker_node;
		struct rb_node *parent_node = NULL;
		struct landlock_rule *new_rule;

		might_sleep();
		lockdep_assert_held(&ruleset->lock);
		if (WARN_ON_ONCE(!object \|\| !layers))
		return -ENOENT;
		walker_node = &(ruleset->root.rb_node);
		while (*walker_node) {
		struct landlock_rule const this = rb_entry(walker_node,
		struct landlock_rule, node);

		if (this->object != object) {
		parent_node = *walker_node;
		if (this->object < object)
		walker_node = &((*walker_node)->rb_right);
		else
		walker_node = &((*walker_node)->rb_left);
		continue;
		}

		/* Only a single-level layer should match an existing rule. */
		if (WARN_ON_ONCE(num_layers != 1))
		return -EINVAL;

		/* If there is a matching rule, updates it. */
		if ((*layers)[0].level == 0) {
		/*
		* Extends access rights when the request comes from
		* landlock_add_rule(2), i.e. @ruleset is not a domain.
		*/
		if (WARN_ON_ONCE(this->num_layers != 1))
		return -EINVAL;
		if (WARN_ON_ONCE(this->layers[0].level != 0))
		return -EINVAL;
		this->layers[0].access \|= (*layers)[0].access;
		return 0;
		}

		if (WARN_ON_ONCE(this->layers[0].level == 0))
		return -EINVAL;

		/*
		* Intersects access rights when it is a merge between a
		* ruleset and a domain.
		*/
		new_rule = create_rule(object, &this->layers, this->num_layers,
		&(*layers)[0]);
		if (IS_ERR(new_rule))
		return PTR_ERR(new_rule);
		rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
		free_rule(this);
		return 0;
		}

		/* There is no match for @object. */
		build_check_ruleset();
		if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
		return -E2BIG;
		new_rule = create_rule(object, layers, num_layers, NULL);
		if (IS_ERR(new_rule))
		return PTR_ERR(new_rule);
		rb_link_node(&new_rule->node, parent_node, walker_node);
		rb_insert_color(&new_rule->node, &ruleset->root);
		ruleset->num_rules++;
		return 0;
		}

		static void build_check_layer(void)
		{
		const struct landlock_layer layer = {
		.level = ~0,
		};

		BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
		}

		/* @ruleset must be locked by the caller. */
		int landlock_insert_rule(struct landlock_ruleset *const ruleset,
		struct landlock_object *const object, const u32 access)
		{
		struct landlock_layer layers[] = {{
		.access = access,
		/* When @level is zero, insert_rule() extends @ruleset. */
		.level = 0,
		}};

		build_check_layer();
		return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
		}

		static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
		{
		if (hierarchy)
		refcount_inc(&hierarchy->usage);
		}

		static void put_hierarchy(struct landlock_hierarchy *hierarchy)
		{
		while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
		const struct landlock_hierarchy *const freeme = hierarchy;

		hierarchy = hierarchy->parent;
		kfree(freeme);
		}
		}

		static int merge_ruleset(struct landlock_ruleset *const dst,
		struct landlock_ruleset *const src)
		{
		struct landlock_rule walker_rule, next_rule;
		int err = 0;

		might_sleep();
		/* Should already be checked by landlock_merge_ruleset() */
		if (WARN_ON_ONCE(!src))
		return 0;
		/* Only merge into a domain. */
		if (WARN_ON_ONCE(!dst \|\| !dst->hierarchy))
		return -EINVAL;

		/* Locks @dst first because we are its only owner. */
		mutex_lock(&dst->lock);
		mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);

		/* Stacks the new layer. */
		if (WARN_ON_ONCE(src->num_layers != 1 \|\| dst->num_layers < 1)) {
		err = -EINVAL;
		goto out_unlock;
		}
		dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];

		/* Merges the @src tree. */
		rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
		&src->root, node) {
		struct landlock_layer layers[] = {{
		.level = dst->num_layers,
		}};

		if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
		err = -EINVAL;
		goto out_unlock;
		}
		if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
		err = -EINVAL;
		goto out_unlock;
		}
		layers[0].access = walker_rule->layers[0].access;
		err = insert_rule(dst, walker_rule->object, &layers,
		ARRAY_SIZE(layers));
		if (err)
		goto out_unlock;
		}

		out_unlock:
		mutex_unlock(&src->lock);
		mutex_unlock(&dst->lock);
		return err;
		}

		static int inherit_ruleset(struct landlock_ruleset *const parent,
		struct landlock_ruleset *const child)
		{
		struct landlock_rule walker_rule, next_rule;
		int err = 0;

		might_sleep();
		if (!parent)
		return 0;

		/* Locks @child first because we are its only owner. */
		mutex_lock(&child->lock);
		mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);

		/* Copies the @parent tree. */
		rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
		&parent->root, node) {
		err = insert_rule(child, walker_rule->object,
		&walker_rule->layers, walker_rule->num_layers);
		if (err)
		goto out_unlock;
		}

		if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
		err = -EINVAL;
		goto out_unlock;
		}
		/* Copies the parent layer stack and leaves a space for the new layer. */
		memcpy(child->fs_access_masks, parent->fs_access_masks,
		flex_array_size(parent, fs_access_masks, parent->num_layers));

		if (WARN_ON_ONCE(!parent->hierarchy)) {
		err = -EINVAL;
		goto out_unlock;
		}
		get_hierarchy(parent->hierarchy);
		child->hierarchy->parent = parent->hierarchy;

		out_unlock:
		mutex_unlock(&parent->lock);
		mutex_unlock(&child->lock);
		return err;
		}

		static void free_ruleset(struct landlock_ruleset *const ruleset)
		{
		struct landlock_rule freeme, next;

		might_sleep();
		rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root,
		node)
		free_rule(freeme);
		put_hierarchy(ruleset->hierarchy);
		kfree(ruleset);
		}

		void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
		{
		might_sleep();
		if (ruleset && refcount_dec_and_test(&ruleset->usage))
		free_ruleset(ruleset);
		}

		static void free_ruleset_work(struct work_struct *const work)
		{
		struct landlock_ruleset *ruleset;

		ruleset = container_of(work, struct landlock_ruleset, work_free);
		free_ruleset(ruleset);
		}

		void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
		{
		if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
		INIT_WORK(&ruleset->work_free, free_ruleset_work);
		schedule_work(&ruleset->work_free);
		}
		}

		/**
		* landlock_merge_ruleset - Merge a ruleset with a domain
		*
		* @parent: Parent domain.
		* @ruleset: New ruleset to be merged.
		*
		* Returns the intersection of @parent and @ruleset, or returns @parent if
		* @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
		*/
		struct landlock_ruleset *landlock_merge_ruleset(
		struct landlock_ruleset *const parent,
		struct landlock_ruleset *const ruleset)
		{
		struct landlock_ruleset *new_dom;
		u32 num_layers;
		int err;

		might_sleep();
		if (WARN_ON_ONCE(!ruleset \|\| parent == ruleset))
		return ERR_PTR(-EINVAL);

		if (parent) {
		if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
		return ERR_PTR(-E2BIG);
		num_layers = parent->num_layers + 1;
		} else {
		num_layers = 1;
		}

		/* Creates a new domain... */
		new_dom = create_ruleset(num_layers);
		if (IS_ERR(new_dom))
		return new_dom;
		new_dom->hierarchy = kzalloc(sizeof(*new_dom->hierarchy),
		GFP_KERNEL_ACCOUNT);
		if (!new_dom->hierarchy) {
		err = -ENOMEM;
		goto out_put_dom;
		}
		refcount_set(&new_dom->hierarchy->usage, 1);

		/* ...as a child of @parent... */
		err = inherit_ruleset(parent, new_dom);
		if (err)
		goto out_put_dom;

		/* ...and including @ruleset. */
		err = merge_ruleset(new_dom, ruleset);
		if (err)
		goto out_put_dom;

		return new_dom;

		out_put_dom:
		landlock_put_ruleset(new_dom);
		return ERR_PTR(err);
		}

		/*
		* The returned access has the same lifetime as @ruleset.
		*/
		const struct landlock_rule *landlock_find_rule(
		const struct landlock_ruleset *const ruleset,
		const struct landlock_object *const object)
		{
		const struct rb_node *node;

		if (!object)
		return NULL;
		node = ruleset->root.rb_node;
		while (node) {
		struct landlock_rule *this = rb_entry(node,
		struct landlock_rule, node);

		if (this->object == object)
		return this;
		if (this->object < object)
		node = node->rb_right;
		else
		node = node->rb_left;
		}
		return NULL;
		}

security/landlock/ruleset.h

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		/* SPDX-License-Identifier: GPL-2.0-only */
		/*
		* Landlock LSM - Ruleset management
		*
		* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
		* Copyright © 2018-2020 ANSSI
		*/

		#ifndef _SECURITY_LANDLOCK_RULESET_H
		#define _SECURITY_LANDLOCK_RULESET_H

		#include <linux/mutex.h>
		#include <linux/rbtree.h>
		#include <linux/refcount.h>
		#include <linux/workqueue.h>

		#include "object.h"

		/**
		* struct landlock_layer - Access rights for a given layer
		*/
		struct landlock_layer {
		/**
		* @level: Position of this layer in the layer stack.
		*/
		u16 level;
		/**
		* @access: Bitfield of allowed actions on the kernel object. They are
		* relative to the object type (e.g. %LANDLOCK_ACTION_FS_READ).
		*/
		u16 access;
		};

		/**
		* struct landlock_rule - Access rights tied to an object
		*/
		struct landlock_rule {
		/**
		* @node: Node in the ruleset's red-black tree.
		*/
		struct rb_node node;
		/**
		* @object: Pointer to identify a kernel object (e.g. an inode). This
		* is used as a key for this ruleset element. This pointer is set once
		* and never modified. It always points to an allocated object because
		* each rule increments the refcount of its object.
		*/
		struct landlock_object *object;
		/**
		* @num_layers: Number of entries in @layers.
		*/
		u32 num_layers;
		/**
		* @layers: Stack of layers, from the latest to the newest, implemented
		* as a flexible array member (FAM).
		*/
		struct landlock_layer layers[];
		};

		/**
		* struct landlock_hierarchy - Node in a ruleset hierarchy
		*/
		struct landlock_hierarchy {
		/**
		* @parent: Pointer to the parent node, or NULL if it is a root
		* Landlock domain.
		*/
		struct landlock_hierarchy *parent;
		/**
		* @usage: Number of potential children domains plus their parent
		* domain.
		*/
		refcount_t usage;
		};

		/**
		* struct landlock_ruleset - Landlock ruleset
		*
		* This data structure must contain unique entries, be updatable, and quick to
		* match an object.
		*/
		struct landlock_ruleset {
		/**
		* @root: Root of a red-black tree containing &struct landlock_rule
		* nodes. Once a ruleset is tied to a process (i.e. as a domain), this
		* tree is immutable until @usage reaches zero.
		*/
		struct rb_root root;
		/**
		* @hierarchy: Enables hierarchy identification even when a parent
		* domain vanishes. This is needed for the ptrace protection.
		*/
		struct landlock_hierarchy *hierarchy;
		union {
		/**
		* @work_free: Enables to free a ruleset within a lockless
		* section. This is only used by
		* landlock_put_ruleset_deferred() when @usage reaches zero.
		* The fields @lock, @usage, @num_rules, @num_layers and
		* @fs_access_masks are then unused.
		*/
		struct work_struct work_free;
		struct {
		/**
		* @lock: Protects against concurrent modifications of
		* @root, if @usage is greater than zero.
		*/
		struct mutex lock;
		/**
		* @usage: Number of processes (i.e. domains) or file
		* descriptors referencing this ruleset.
		*/
		refcount_t usage;
		/**
		* @num_rules: Number of non-overlapping (i.e. not for
		* the same object) rules in this ruleset.
		*/
		u32 num_rules;
		/**
		* @num_layers: Number of layers that are used in this
		* ruleset. This enables to check that all the layers
		* allow an access request. A value of 0 identifies a
		* non-merged ruleset (i.e. not a domain).
		*/
		u32 num_layers;
		/**
		* @fs_access_masks: Contains the subset of filesystem
		* actions that are restricted by a ruleset. A domain
		* saves all layers of merged rulesets in a stack
		* (FAM), starting from the first layer to the last
		* one. These layers are used when merging rulesets,
		* for user space backward compatibility (i.e.
		* future-proof), and to properly handle merged
		* rulesets without overlapping access rights. These
		* layers are set once and never changed for the
		* lifetime of the ruleset.
		*/
		u16 fs_access_masks[];
		};
		};
		};

		struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask);

		void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
		void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);

		int landlock_insert_rule(struct landlock_ruleset *const ruleset,
		struct landlock_object *const object, const u32 access);

		struct landlock_ruleset *landlock_merge_ruleset(
		struct landlock_ruleset *const parent,
		struct landlock_ruleset *const ruleset);

		const struct landlock_rule *landlock_find_rule(
		const struct landlock_ruleset *const ruleset,
		const struct landlock_object *const object);

		static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
		{
		if (ruleset)
		refcount_inc(&ruleset->usage);
		}

		#endif /* _SECURITY_LANDLOCK_RULESET_H */