// 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/cleanup.h>
#include <linux/compiler_types.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
#include <linux/mutex.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 "access.h"
#include "domain.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_flex(*new_ruleset, 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_inode = RB_ROOT;

#if IS_ENABLED(CONFIG_INET)
        new_ruleset->root_net_port = RB_ROOT;
#endif /* IS_ENABLED(CONFIG_INET) */

        new_ruleset->num_layers = num_layers;
        /*
         * hierarchy = NULL
         * num_rules = 0
         * access_masks[] = 0
         */
        return new_ruleset;
}

struct landlock_ruleset *
landlock_create_ruleset(const access_mask_t fs_access_mask,
                        const access_mask_t net_access_mask,
                        const access_mask_t scope_mask)
{
        struct landlock_ruleset *new_ruleset;

        /* Informs about useless ruleset. */
        if (!fs_access_mask && !net_access_mask && !scope_mask)
                return ERR_PTR(-ENOMSG);
        new_ruleset = create_ruleset(1);
        if (IS_ERR(new_ruleset))
                return new_ruleset;
        if (fs_access_mask)
                landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
        if (net_access_mask)
                landlock_add_net_access_mask(new_ruleset, net_access_mask, 0);
        if (scope_mask)
                landlock_add_scope_mask(new_ruleset, scope_mask, 0);
        return new_ruleset;
}

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

        /*
         * Checks that .num_layers is large enough for at least
         * LANDLOCK_MAX_NUM_LAYERS layers.
         */
        BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
}

static bool is_object_pointer(const enum landlock_key_type key_type)
{
        switch (key_type) {
        case LANDLOCK_KEY_INODE:
                return true;

#if IS_ENABLED(CONFIG_INET)
        case LANDLOCK_KEY_NET_PORT:
                return false;
#endif /* IS_ENABLED(CONFIG_INET) */

        default:
                WARN_ON_ONCE(1);
                return false;
        }
}

static struct landlock_rule *
create_rule(const struct landlock_id id,
            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_flex(*new_rule, layers, new_num_layers,
                                GFP_KERNEL_ACCOUNT);
        if (!new_rule)
                return ERR_PTR(-ENOMEM);
        RB_CLEAR_NODE(&new_rule->node);
        if (is_object_pointer(id.type)) {
                /* This should have been caught by insert_rule(). */
                WARN_ON_ONCE(!id.key.object);
                landlock_get_object(id.key.object);
        }

        new_rule->key = id.key;
        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 struct rb_root *get_root(struct landlock_ruleset *const ruleset,
                                const enum landlock_key_type key_type)
{
        switch (key_type) {
        case LANDLOCK_KEY_INODE:
                return &ruleset->root_inode;

#if IS_ENABLED(CONFIG_INET)
        case LANDLOCK_KEY_NET_PORT:
                return &ruleset->root_net_port;
#endif /* IS_ENABLED(CONFIG_INET) */

        default:
                WARN_ON_ONCE(1);
                return ERR_PTR(-EINVAL);
        }
}

static void free_rule(struct landlock_rule *const rule,
                      const enum landlock_key_type key_type)
{
        might_sleep();
        if (!rule)
                return;
        if (is_object_pointer(key_type))
                landlock_put_object(rule->key.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.
 * @id: The ID to build the new rule with.  The underlying kernel object, if
 *      any, 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,
                       const struct landlock_id id,
                       const struct landlock_layer (*const layers)[],
                       const size_t num_layers)
{
        struct rb_node **walker_node;
        struct rb_node *parent_node = NULL;
        struct landlock_rule *new_rule;
        struct rb_root *root;

        might_sleep();
        lockdep_assert_held(&ruleset->lock);
        if (WARN_ON_ONCE(!layers))
                return -ENOENT;

        if (is_object_pointer(id.type) && WARN_ON_ONCE(!id.key.object))
                return -ENOENT;

        root = get_root(ruleset, id.type);
        if (IS_ERR(root))
                return PTR_ERR(root);

        walker_node = &root->rb_node;
        while (*walker_node) {
                struct landlock_rule *const this =
                        rb_entry(*walker_node, struct landlock_rule, node);

                if (this->key.data != id.key.data) {
                        parent_node = *walker_node;
                        if (this->key.data < id.key.data)
                                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(id, &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, root);
                free_rule(this, id.type);
                return 0;
        }

        /* There is no match for @id. */
        build_check_ruleset();
        if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
                return -E2BIG;
        new_rule = create_rule(id, 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, root);
        ruleset->num_rules++;
        return 0;
}

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

        /*
         * Checks that .level and .access are large enough to contain their expected
         * maximum values.
         */
        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,
                         const struct landlock_id id,
                         const access_mask_t access)
{
        struct landlock_layer layers[] = { {
                .access = access,
                /* When @level is zero, insert_rule() extends @ruleset. */
                .level = 0,
        } };

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

static int merge_tree(struct landlock_ruleset *const dst,
                      struct landlock_ruleset *const src,
                      const enum landlock_key_type key_type)
{
        struct landlock_rule *walker_rule, *next_rule;
        struct rb_root *src_root;
        int err = 0;

        might_sleep();
        lockdep_assert_held(&dst->lock);
        lockdep_assert_held(&src->lock);

        src_root = get_root(src, key_type);
        if (IS_ERR(src_root))
                return PTR_ERR(src_root);

        /* 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,
                } };
                const struct landlock_id id = {
                        .key = walker_rule->key,
                        .type = key_type,
                };

                if (WARN_ON_ONCE(walker_rule->num_layers != 1))
                        return -EINVAL;

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

                layers[0].access = walker_rule->layers[0].access;

                err = insert_rule(dst, id, &layers, ARRAY_SIZE(layers));
                if (err)
                        return err;
        }
        return err;
}

static int merge_ruleset(struct landlock_ruleset *const dst,
                         struct landlock_ruleset *const src)
{
        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->access_masks[dst->num_layers - 1] =
                landlock_upgrade_handled_access_masks(src->access_masks[0]);

        /* Merges the @src inode tree. */
        err = merge_tree(dst, src, LANDLOCK_KEY_INODE);
        if (err)
                goto out_unlock;

#if IS_ENABLED(CONFIG_INET)
        /* Merges the @src network port tree. */
        err = merge_tree(dst, src, LANDLOCK_KEY_NET_PORT);
        if (err)
                goto out_unlock;
#endif /* IS_ENABLED(CONFIG_INET) */

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

static int inherit_tree(struct landlock_ruleset *const parent,
                        struct landlock_ruleset *const child,
                        const enum landlock_key_type key_type)
{
        struct landlock_rule *walker_rule, *next_rule;
        struct rb_root *parent_root;
        int err = 0;

        might_sleep();
        lockdep_assert_held(&parent->lock);
        lockdep_assert_held(&child->lock);

        parent_root = get_root(parent, key_type);
        if (IS_ERR(parent_root))
                return PTR_ERR(parent_root);

        /* Copies the @parent inode or network tree. */
        rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
                                             parent_root, node) {
                const struct landlock_id id = {
                        .key = walker_rule->key,
                        .type = key_type,
                };

                err = insert_rule(child, id, &walker_rule->layers,
                                  walker_rule->num_layers);
                if (err)
                        return err;
        }
        return err;
}

static int inherit_ruleset(struct landlock_ruleset *const parent,
                           struct landlock_ruleset *const child)
{
        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 inode tree. */
        err = inherit_tree(parent, child, LANDLOCK_KEY_INODE);
        if (err)
                goto out_unlock;

#if IS_ENABLED(CONFIG_INET)
        /* Copies the @parent network port tree. */
        err = inherit_tree(parent, child, LANDLOCK_KEY_NET_PORT);
        if (err)
                goto out_unlock;
#endif /* IS_ENABLED(CONFIG_INET) */

        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->access_masks, parent->access_masks,
               flex_array_size(parent, access_masks, parent->num_layers));

        if (WARN_ON_ONCE(!parent->hierarchy)) {
                err = -EINVAL;
                goto out_unlock;
        }
        landlock_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_inode,
                                             node)
                free_rule(freeme, LANDLOCK_KEY_INODE);

#if IS_ENABLED(CONFIG_INET)
        rbtree_postorder_for_each_entry_safe(freeme, next,
                                             &ruleset->root_net_port, node)
                free_rule(freeme, LANDLOCK_KEY_NET_PORT);
#endif /* IS_ENABLED(CONFIG_INET) */

        landlock_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);
}

/* Only called by hook_cred_free(). */
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.
 *
 * The current task is requesting to be restricted.  The subjective credentials
 * must not be in an overridden state. cf. landlock_init_hierarchy_log().
 *
 * 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 __free(landlock_put_ruleset) = NULL;
        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_obj(*new_dom->hierarchy, GFP_KERNEL_ACCOUNT);
        if (!new_dom->hierarchy)
                return ERR_PTR(-ENOMEM);

        refcount_set(&new_dom->hierarchy->usage, 1);

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

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

        err = landlock_init_hierarchy_log(new_dom->hierarchy);
        if (err)
                return ERR_PTR(err);

        return no_free_ptr(new_dom);
}

/*
 * 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_id id)
{
        const struct rb_root *root;
        const struct rb_node *node;

        root = get_root((struct landlock_ruleset *)ruleset, id.type);
        if (IS_ERR(root))
                return NULL;
        node = root->rb_node;

        while (node) {
                struct landlock_rule *this =
                        rb_entry(node, struct landlock_rule, node);

                if (this->key.data == id.key.data)
                        return this;
                if (this->key.data < id.key.data)
                        node = node->rb_right;
                else
                        node = node->rb_left;
        }
        return NULL;
}

/**
 * landlock_unmask_layers - Remove the access rights in @masks
 *                          which are granted in @rule
 *
 * Updates the set of (per-layer) unfulfilled access rights @masks
 * so that all the access rights granted in @rule are removed from it
 * (because they are now fulfilled).
 *
 * @rule: A rule that grants a set of access rights for each layer
 * @masks: A matrix of unfulfilled access rights for each layer
 *
 * Returns true if the request is allowed (i.e. the access rights granted all
 * remaining unfulfilled access rights and masks has no leftover set bits).
 */
bool landlock_unmask_layers(const struct landlock_rule *const rule,
                            struct layer_access_masks *masks)
{
        if (!masks)
                return true;
        if (!rule)
                return false;

        /*
         * An access is granted if, for each policy layer, at least one rule
         * encountered on the pathwalk grants the requested access,
         * regardless of its position in the layer stack.  We must then check
         * the remaining layers for each inode, from the first added layer to
         * the last one.  When there is multiple requested accesses, for each
         * policy layer, the full set of requested accesses may not be granted
         * by only one rule, but by the union (binary OR) of multiple rules.
         * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
         */
        for (size_t i = 0; i < rule->num_layers; i++) {
                const struct landlock_layer *const layer = &rule->layers[i];

                /* Clear the bits where the layer in the rule grants access. */
                masks->access[layer->level - 1] &= ~layer->access;
        }

        for (size_t i = 0; i < ARRAY_SIZE(masks->access); i++) {
                if (masks->access[i])
                        return false;
        }
        return true;
}

typedef access_mask_t
get_access_mask_t(const struct landlock_ruleset *const ruleset,
                  const u16 layer_level);

/**
 * landlock_init_layer_masks - Initialize layer masks from an access request
 *
 * Populates @masks such that for each access right in @access_request,
 * the bits for all the layers are set where this access right is handled.
 *
 * @domain: The domain that defines the current restrictions.
 * @access_request: The requested access rights to check.
 * @masks: Layer access masks to populate.
 * @key_type: The key type to switch between access masks of different types.
 *
 * Returns: An access mask where each access right bit is set which is handled
 * in any of the active layers in @domain.
 */
access_mask_t
landlock_init_layer_masks(const struct landlock_ruleset *const domain,
                          const access_mask_t access_request,
                          struct layer_access_masks *const masks,
                          const enum landlock_key_type key_type)
{
        access_mask_t handled_accesses = 0;
        get_access_mask_t *get_access_mask;

        switch (key_type) {
        case LANDLOCK_KEY_INODE:
                get_access_mask = landlock_get_fs_access_mask;
                break;

#if IS_ENABLED(CONFIG_INET)
        case LANDLOCK_KEY_NET_PORT:
                get_access_mask = landlock_get_net_access_mask;
                break;
#endif /* IS_ENABLED(CONFIG_INET) */

        default:
                WARN_ON_ONCE(1);
                return 0;
        }

        /* An empty access request can happen because of O_WRONLY | O_RDWR. */
        if (!access_request)
                return 0;

        for (size_t i = 0; i < domain->num_layers; i++) {
                const access_mask_t handled = get_access_mask(domain, i);

                masks->access[i] = access_request & handled;
                handled_accesses |= masks->access[i];
        }
        for (size_t i = domain->num_layers; i < ARRAY_SIZE(masks->access); i++)
                masks->access[i] = 0;

        return handled_accesses;
}