// 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,
        };
        typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;

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

/**
 * 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,
                .access = ~0,
        };

        BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
        BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
}

/* @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;
}