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![Mickaël Salaün](/assets/img/avatar_default.png)
Create and use the access_mask_t typedef to enforce a consistent access mask size and uniformly use a 16-bits type. This will helps transition to a 32-bits value one day. Add a build check to make sure all (filesystem) access rights fit in. This will be extended with a following commit. Reviewed-by: Paul Moore <paul@paul-moore.com> Link: https://lore.kernel.org/r/20220506161102.525323-2-mic@digikod.net Cc: stable@vger.kernel.org Signed-off-by: Mickaël Salaün <mic@digikod.net>
475 lines
12 KiB
C
475 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Landlock LSM - Ruleset management
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*
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* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2018-2020 ANSSI
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*/
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#include <linux/bits.h>
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#include <linux/bug.h>
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#include <linux/compiler_types.h>
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#include <linux/err.h>
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#include <linux/errno.h>
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#include <linux/kernel.h>
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#include <linux/lockdep.h>
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#include <linux/overflow.h>
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#include <linux/rbtree.h>
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#include <linux/refcount.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/workqueue.h>
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#include "limits.h"
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#include "object.h"
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#include "ruleset.h"
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static struct landlock_ruleset *create_ruleset(const u32 num_layers)
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{
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struct landlock_ruleset *new_ruleset;
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new_ruleset =
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kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers),
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GFP_KERNEL_ACCOUNT);
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if (!new_ruleset)
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return ERR_PTR(-ENOMEM);
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refcount_set(&new_ruleset->usage, 1);
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mutex_init(&new_ruleset->lock);
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new_ruleset->root = RB_ROOT;
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new_ruleset->num_layers = num_layers;
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/*
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* hierarchy = NULL
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* num_rules = 0
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* fs_access_masks[] = 0
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*/
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return new_ruleset;
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}
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struct landlock_ruleset *
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landlock_create_ruleset(const access_mask_t fs_access_mask)
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{
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struct landlock_ruleset *new_ruleset;
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/* Informs about useless ruleset. */
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if (!fs_access_mask)
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return ERR_PTR(-ENOMSG);
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new_ruleset = create_ruleset(1);
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if (!IS_ERR(new_ruleset))
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new_ruleset->fs_access_masks[0] = fs_access_mask;
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return new_ruleset;
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}
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static void build_check_rule(void)
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{
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const struct landlock_rule rule = {
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.num_layers = ~0,
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};
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BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
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}
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static struct landlock_rule *
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create_rule(struct landlock_object *const object,
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const struct landlock_layer (*const layers)[], const u32 num_layers,
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const struct landlock_layer *const new_layer)
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{
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struct landlock_rule *new_rule;
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u32 new_num_layers;
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build_check_rule();
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if (new_layer) {
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/* Should already be checked by landlock_merge_ruleset(). */
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if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
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return ERR_PTR(-E2BIG);
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new_num_layers = num_layers + 1;
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} else {
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new_num_layers = num_layers;
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}
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new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
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GFP_KERNEL_ACCOUNT);
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if (!new_rule)
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return ERR_PTR(-ENOMEM);
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RB_CLEAR_NODE(&new_rule->node);
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landlock_get_object(object);
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new_rule->object = object;
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new_rule->num_layers = new_num_layers;
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/* Copies the original layer stack. */
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memcpy(new_rule->layers, layers,
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flex_array_size(new_rule, layers, num_layers));
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if (new_layer)
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/* Adds a copy of @new_layer on the layer stack. */
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new_rule->layers[new_rule->num_layers - 1] = *new_layer;
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return new_rule;
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}
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static void free_rule(struct landlock_rule *const rule)
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{
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might_sleep();
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if (!rule)
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return;
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landlock_put_object(rule->object);
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kfree(rule);
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}
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static void build_check_ruleset(void)
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{
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const struct landlock_ruleset ruleset = {
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.num_rules = ~0,
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.num_layers = ~0,
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};
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typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
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BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
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BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
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BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
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}
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/**
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* insert_rule - Create and insert a rule in a ruleset
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*
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* @ruleset: The ruleset to be updated.
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* @object: The object to build the new rule with. The underlying kernel
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* object must be held by the caller.
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* @layers: One or multiple layers to be copied into the new rule.
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* @num_layers: The number of @layers entries.
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*
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* When user space requests to add a new rule to a ruleset, @layers only
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* contains one entry and this entry is not assigned to any level. In this
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* case, the new rule will extend @ruleset, similarly to a boolean OR between
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* access rights.
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*
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* When merging a ruleset in a domain, or copying a domain, @layers will be
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* added to @ruleset as new constraints, similarly to a boolean AND between
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* access rights.
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*/
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static int insert_rule(struct landlock_ruleset *const ruleset,
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struct landlock_object *const object,
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const struct landlock_layer (*const layers)[],
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size_t num_layers)
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{
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struct rb_node **walker_node;
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struct rb_node *parent_node = NULL;
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struct landlock_rule *new_rule;
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might_sleep();
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lockdep_assert_held(&ruleset->lock);
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if (WARN_ON_ONCE(!object || !layers))
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return -ENOENT;
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walker_node = &(ruleset->root.rb_node);
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while (*walker_node) {
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struct landlock_rule *const this =
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rb_entry(*walker_node, struct landlock_rule, node);
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if (this->object != object) {
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parent_node = *walker_node;
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if (this->object < object)
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walker_node = &((*walker_node)->rb_right);
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else
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walker_node = &((*walker_node)->rb_left);
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continue;
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}
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/* Only a single-level layer should match an existing rule. */
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if (WARN_ON_ONCE(num_layers != 1))
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return -EINVAL;
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/* If there is a matching rule, updates it. */
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if ((*layers)[0].level == 0) {
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/*
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* Extends access rights when the request comes from
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* landlock_add_rule(2), i.e. @ruleset is not a domain.
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*/
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if (WARN_ON_ONCE(this->num_layers != 1))
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return -EINVAL;
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if (WARN_ON_ONCE(this->layers[0].level != 0))
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return -EINVAL;
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this->layers[0].access |= (*layers)[0].access;
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return 0;
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}
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if (WARN_ON_ONCE(this->layers[0].level == 0))
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return -EINVAL;
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/*
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* Intersects access rights when it is a merge between a
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* ruleset and a domain.
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*/
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new_rule = create_rule(object, &this->layers, this->num_layers,
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&(*layers)[0]);
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if (IS_ERR(new_rule))
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return PTR_ERR(new_rule);
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rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
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free_rule(this);
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return 0;
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}
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/* There is no match for @object. */
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build_check_ruleset();
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if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
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return -E2BIG;
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new_rule = create_rule(object, layers, num_layers, NULL);
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if (IS_ERR(new_rule))
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return PTR_ERR(new_rule);
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rb_link_node(&new_rule->node, parent_node, walker_node);
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rb_insert_color(&new_rule->node, &ruleset->root);
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ruleset->num_rules++;
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return 0;
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}
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static void build_check_layer(void)
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{
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const struct landlock_layer layer = {
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.level = ~0,
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.access = ~0,
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};
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BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
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BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
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}
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/* @ruleset must be locked by the caller. */
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int landlock_insert_rule(struct landlock_ruleset *const ruleset,
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struct landlock_object *const object,
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const access_mask_t access)
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{
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struct landlock_layer layers[] = { {
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.access = access,
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/* When @level is zero, insert_rule() extends @ruleset. */
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.level = 0,
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} };
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build_check_layer();
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return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
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}
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static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
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{
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if (hierarchy)
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refcount_inc(&hierarchy->usage);
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}
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static void put_hierarchy(struct landlock_hierarchy *hierarchy)
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{
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while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
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const struct landlock_hierarchy *const freeme = hierarchy;
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hierarchy = hierarchy->parent;
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kfree(freeme);
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}
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}
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static int merge_ruleset(struct landlock_ruleset *const dst,
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struct landlock_ruleset *const src)
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{
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struct landlock_rule *walker_rule, *next_rule;
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int err = 0;
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might_sleep();
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/* Should already be checked by landlock_merge_ruleset() */
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if (WARN_ON_ONCE(!src))
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return 0;
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/* Only merge into a domain. */
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if (WARN_ON_ONCE(!dst || !dst->hierarchy))
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return -EINVAL;
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/* Locks @dst first because we are its only owner. */
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mutex_lock(&dst->lock);
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mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
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/* Stacks the new layer. */
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if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
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err = -EINVAL;
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goto out_unlock;
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}
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dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
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/* Merges the @src tree. */
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rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root,
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node) {
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struct landlock_layer layers[] = { {
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.level = dst->num_layers,
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} };
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if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
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err = -EINVAL;
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goto out_unlock;
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}
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if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
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err = -EINVAL;
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goto out_unlock;
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}
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layers[0].access = walker_rule->layers[0].access;
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err = insert_rule(dst, walker_rule->object, &layers,
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ARRAY_SIZE(layers));
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if (err)
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goto out_unlock;
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}
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out_unlock:
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mutex_unlock(&src->lock);
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mutex_unlock(&dst->lock);
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return err;
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}
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static int inherit_ruleset(struct landlock_ruleset *const parent,
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struct landlock_ruleset *const child)
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{
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struct landlock_rule *walker_rule, *next_rule;
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int err = 0;
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might_sleep();
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if (!parent)
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return 0;
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/* Locks @child first because we are its only owner. */
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mutex_lock(&child->lock);
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mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
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/* Copies the @parent tree. */
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rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
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&parent->root, node) {
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err = insert_rule(child, walker_rule->object,
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&walker_rule->layers,
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walker_rule->num_layers);
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if (err)
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goto out_unlock;
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}
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if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
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err = -EINVAL;
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goto out_unlock;
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}
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/* Copies the parent layer stack and leaves a space for the new layer. */
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memcpy(child->fs_access_masks, parent->fs_access_masks,
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flex_array_size(parent, fs_access_masks, parent->num_layers));
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if (WARN_ON_ONCE(!parent->hierarchy)) {
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err = -EINVAL;
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goto out_unlock;
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}
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get_hierarchy(parent->hierarchy);
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child->hierarchy->parent = parent->hierarchy;
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out_unlock:
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mutex_unlock(&parent->lock);
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mutex_unlock(&child->lock);
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return err;
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}
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static void free_ruleset(struct landlock_ruleset *const ruleset)
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{
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struct landlock_rule *freeme, *next;
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might_sleep();
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rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root, node)
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free_rule(freeme);
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put_hierarchy(ruleset->hierarchy);
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kfree(ruleset);
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}
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void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
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{
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might_sleep();
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if (ruleset && refcount_dec_and_test(&ruleset->usage))
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free_ruleset(ruleset);
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}
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static void free_ruleset_work(struct work_struct *const work)
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{
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struct landlock_ruleset *ruleset;
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ruleset = container_of(work, struct landlock_ruleset, work_free);
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free_ruleset(ruleset);
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}
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void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
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{
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if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
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INIT_WORK(&ruleset->work_free, free_ruleset_work);
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schedule_work(&ruleset->work_free);
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}
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}
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/**
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* landlock_merge_ruleset - Merge a ruleset with a domain
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*
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* @parent: Parent domain.
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* @ruleset: New ruleset to be merged.
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*
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* Returns the intersection of @parent and @ruleset, or returns @parent if
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* @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
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*/
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struct landlock_ruleset *
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landlock_merge_ruleset(struct landlock_ruleset *const parent,
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struct landlock_ruleset *const ruleset)
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{
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struct landlock_ruleset *new_dom;
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u32 num_layers;
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int err;
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might_sleep();
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if (WARN_ON_ONCE(!ruleset || parent == ruleset))
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return ERR_PTR(-EINVAL);
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if (parent) {
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if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
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return ERR_PTR(-E2BIG);
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num_layers = parent->num_layers + 1;
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} else {
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num_layers = 1;
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}
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/* Creates a new domain... */
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new_dom = create_ruleset(num_layers);
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if (IS_ERR(new_dom))
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return new_dom;
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new_dom->hierarchy =
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kzalloc(sizeof(*new_dom->hierarchy), GFP_KERNEL_ACCOUNT);
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if (!new_dom->hierarchy) {
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err = -ENOMEM;
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goto out_put_dom;
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}
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refcount_set(&new_dom->hierarchy->usage, 1);
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/* ...as a child of @parent... */
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err = inherit_ruleset(parent, new_dom);
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if (err)
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goto out_put_dom;
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/* ...and including @ruleset. */
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err = merge_ruleset(new_dom, ruleset);
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if (err)
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goto out_put_dom;
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return new_dom;
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out_put_dom:
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landlock_put_ruleset(new_dom);
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return ERR_PTR(err);
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}
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/*
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* The returned access has the same lifetime as @ruleset.
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*/
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const struct landlock_rule *
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landlock_find_rule(const struct landlock_ruleset *const ruleset,
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const struct landlock_object *const object)
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{
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const struct rb_node *node;
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if (!object)
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return NULL;
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node = ruleset->root.rb_node;
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while (node) {
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struct landlock_rule *this =
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rb_entry(node, struct landlock_rule, node);
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if (this->object == object)
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return this;
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if (this->object < object)
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node = node->rb_right;
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else
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node = node->rb_left;
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}
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return NULL;
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}
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