audit_tree.c

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#include "audit.h"
#include <linux/fsnotify_backend.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/kthread.h>
#include <linux/slab.h>

struct audit_tree;
struct audit_chunk;

struct audit_tree {
    atomic_t count;
    int goner;
    struct audit_chunk *root;
    struct list_head chunks;
    struct list_head rules;
    struct list_head list;
    struct list_head same_root;
    struct rcu_head head;
    char pathname[];
};

struct audit_chunk {
    struct list_head hash;
    struct fsnotify_mark mark;
    struct list_head trees;     /* with root here */
    int dead;
    int count;
    atomic_long_t refs;
    struct rcu_head head;
    struct node {
        struct list_head list;
        struct audit_tree *owner;
        unsigned index;     /* index; upper bit indicates 'will prune' */
    } owners[];
};

static LIST_HEAD(tree_list);
static LIST_HEAD(prune_list);

/*
 * One struct chunk is attached to each inode of interest.
 * We replace struct chunk on tagging/untagging.
 * Rules have pointer to struct audit_tree.
 * Rules have struct list_head rlist forming a list of rules over
 * the same tree.
 * References to struct chunk are collected at audit_inode{,_child}()
 * time and used in AUDIT_TREE rule matching.
 * These references are dropped at the same time we are calling
 * audit_free_names(), etc.
 *
 * Cyclic lists galore:
 * tree.chunks anchors chunk.owners[].list          hash_lock
 * tree.rules anchors rule.rlist                audit_filter_mutex
 * chunk.trees anchors tree.same_root               hash_lock
 * chunk.hash is a hash with middle bits of watch.inode as
 * a hash function.                     RCU, hash_lock
 *
 * tree is refcounted; one reference for "some rules on rules_list refer to
 * it", one for each chunk with pointer to it.
 *
 * chunk is refcounted by embedded fsnotify_mark + .refs (non-zero refcount
 * of watch contributes 1 to .refs).
 *
 * node.index allows to get from node.list to containing chunk.
 * MSB of that sucker is stolen to mark taggings that we might have to
 * revert - several operations have very unpleasant cleanup logics and
 * that makes a difference.  Some.
 */

static struct fsnotify_group *audit_tree_group;

static struct audit_tree *alloc_tree(const char *s)
{
    struct audit_tree *tree;

    tree = kmalloc(sizeof(struct audit_tree) + strlen(s) + 1, GFP_KERNEL);
    if (tree) {
        atomic_set(&tree->count, 1);
        tree->goner = 0;
        INIT_LIST_HEAD(&tree->chunks);
        INIT_LIST_HEAD(&tree->rules);
        INIT_LIST_HEAD(&tree->list);
        INIT_LIST_HEAD(&tree->same_root);
        tree->root = NULL;
        strcpy(tree->pathname, s);
    }
    return tree;
}

static inline void get_tree(struct audit_tree *tree)
{
    atomic_inc(&tree->count);
}

static inline void put_tree(struct audit_tree *tree)
{
    if (atomic_dec_and_test(&tree->count))
        kfree_rcu(tree, head);
}

/* to avoid bringing the entire thing in audit.h */
const char *audit_tree_path(struct audit_tree *tree)
{
    return tree->pathname;
}

static void free_chunk(struct audit_chunk *chunk)
{
    int i;

    for (i = 0; i < chunk->count; i++) {
        if (chunk->owners[i].owner)
            put_tree(chunk->owners[i].owner);
    }
    kfree(chunk);
}

void audit_put_chunk(struct audit_chunk *chunk)
{
    if (atomic_long_dec_and_test(&chunk->refs))
        free_chunk(chunk);
}

static void __put_chunk(struct rcu_head *rcu)
{
    struct audit_chunk *chunk = container_of(rcu, struct audit_chunk, head);
    audit_put_chunk(chunk);
}

static void audit_tree_destroy_watch(struct fsnotify_mark *entry)
{
    struct audit_chunk *chunk = container_of(entry, struct audit_chunk, mark);
    call_rcu(&chunk->head, __put_chunk);
}

static struct audit_chunk *alloc_chunk(int count)
{
    struct audit_chunk *chunk;
    size_t size;
    int i;

    size = offsetof(struct audit_chunk, owners) + count * sizeof(struct node);
    chunk = kzalloc(size, GFP_KERNEL);
    if (!chunk)
        return NULL;

    INIT_LIST_HEAD(&chunk->hash);
    INIT_LIST_HEAD(&chunk->trees);
    chunk->count = count;
    atomic_long_set(&chunk->refs, 1);
    for (i = 0; i < count; i++) {
        INIT_LIST_HEAD(&chunk->owners[i].list);
        chunk->owners[i].index = i;
    }
    fsnotify_init_mark(&chunk->mark, audit_tree_destroy_watch);
    return chunk;
}

enum {HASH_SIZE = 128};
static struct list_head chunk_hash_heads[HASH_SIZE];
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(hash_lock);

static inline struct list_head *chunk_hash(const struct inode *inode)
{
    unsigned long n = (unsigned long)inode / L1_CACHE_BYTES;
    return chunk_hash_heads + n % HASH_SIZE;
}

/* hash_lock & entry->lock is held by caller */
static void insert_hash(struct audit_chunk *chunk)
{
    struct fsnotify_mark *entry = &chunk->mark;
    struct list_head *list;

    if (!entry->i.inode)
        return;
    list = chunk_hash(entry->i.inode);
    list_add_rcu(&chunk->hash, list);
}

/* called under rcu_read_lock */
struct audit_chunk *audit_tree_lookup(const struct inode *inode)
{
    struct list_head *list = chunk_hash(inode);
    struct audit_chunk *p;

    list_for_each_entry_rcu(p, list, hash) {
        /* mark.inode may have gone NULL, but who cares? */
        if (p->mark.i.inode == inode) {
            atomic_long_inc(&p->refs);
            return p;
        }
    }
    return NULL;
}

int audit_tree_match(struct audit_chunk *chunk, struct audit_tree *tree)
{
    int n;
    for (n = 0; n < chunk->count; n++)
        if (chunk->owners[n].owner == tree)
            return 1;
    return 0;
}

/* tagging and untagging inodes with trees */

static struct audit_chunk *find_chunk(struct node *p)
{
    int index = p->index & ~(1U<<31);
    p -= index;
    return container_of(p, struct audit_chunk, owners[0]);
}

static void untag_chunk(struct node *p)
{
    struct audit_chunk *chunk = find_chunk(p);
    struct fsnotify_mark *entry = &chunk->mark;
    struct audit_chunk *new = NULL;
    struct audit_tree *owner;
    int size = chunk->count - 1;
    int i, j;

    fsnotify_get_mark(entry);

    spin_unlock(&hash_lock);

    if (size)
        new = alloc_chunk(size);

    spin_lock(&entry->lock);
    if (chunk->dead || !entry->i.inode) {
        spin_unlock(&entry->lock);
        if (new)
            free_chunk(new);
        goto out;
    }

    owner = p->owner;

    if (!size) {
        chunk->dead = 1;
        spin_lock(&hash_lock);
        list_del_init(&chunk->trees);
        if (owner->root == chunk)
            owner->root = NULL;
        list_del_init(&p->list);
        list_del_rcu(&chunk->hash);
        spin_unlock(&hash_lock);
        spin_unlock(&entry->lock);
        fsnotify_destroy_mark(entry);
        goto out;
    }

    if (!new)
        goto Fallback;

    fsnotify_duplicate_mark(&new->mark, entry);
    if (fsnotify_add_mark(&new->mark, new->mark.group, new->mark.i.inode, NULL, 1)) {
        fsnotify_put_mark(&new->mark);
        goto Fallback;
    }

    chunk->dead = 1;
    spin_lock(&hash_lock);
    list_replace_init(&chunk->trees, &new->trees);
    if (owner->root == chunk) {
        list_del_init(&owner->same_root);
        owner->root = NULL;
    }

    for (i = j = 0; j <= size; i++, j++) {
        struct audit_tree *s;
        if (&chunk->owners[j] == p) {
            list_del_init(&p->list);
            i--;
            continue;
        }
        s = chunk->owners[j].owner;
        new->owners[i].owner = s;
        new->owners[i].index = chunk->owners[j].index - j + i;
        if (!s) /* result of earlier fallback */
            continue;
        get_tree(s);
        list_replace_init(&chunk->owners[j].list, &new->owners[i].list);
    }

    list_replace_rcu(&chunk->hash, &new->hash);
    list_for_each_entry(owner, &new->trees, same_root)
        owner->root = new;
    spin_unlock(&hash_lock);
    spin_unlock(&entry->lock);
    fsnotify_destroy_mark(entry);
    fsnotify_put_mark(&new->mark);  /* drop initial reference */
    goto out;

Fallback:
    // do the best we can
    spin_lock(&hash_lock);
    if (owner->root == chunk) {
        list_del_init(&owner->same_root);
        owner->root = NULL;
    }
    list_del_init(&p->list);
    p->owner = NULL;
    put_tree(owner);
    spin_unlock(&hash_lock);
    spin_unlock(&entry->lock);
out:
    fsnotify_put_mark(entry);
    spin_lock(&hash_lock);
}

static int create_chunk(struct inode *inode, struct audit_tree *tree)
{
    struct fsnotify_mark *entry;
    struct audit_chunk *chunk = alloc_chunk(1);
    if (!chunk)
        return -ENOMEM;

    entry = &chunk->mark;
    if (fsnotify_add_mark(entry, audit_tree_group, inode, NULL, 0)) {
        fsnotify_put_mark(entry);
        return -ENOSPC;
    }

    spin_lock(&entry->lock);
    spin_lock(&hash_lock);
    if (tree->goner) {
        spin_unlock(&hash_lock);
        chunk->dead = 1;
        spin_unlock(&entry->lock);
        fsnotify_destroy_mark(entry);
        fsnotify_put_mark(entry);
        return 0;
    }
    chunk->owners[0].index = (1U << 31);
    chunk->owners[0].owner = tree;
    get_tree(tree);
    list_add(&chunk->owners[0].list, &tree->chunks);
    if (!tree->root) {
        tree->root = chunk;
        list_add(&tree->same_root, &chunk->trees);
    }
    insert_hash(chunk);
    spin_unlock(&hash_lock);
    spin_unlock(&entry->lock);
    fsnotify_put_mark(entry);   /* drop initial reference */
    return 0;
}

/* the first tagged inode becomes root of tree */
static int tag_chunk(struct inode *inode, struct audit_tree *tree)
{
    struct fsnotify_mark *old_entry, *chunk_entry;
    struct audit_tree *owner;
    struct audit_chunk *chunk, *old;
    struct node *p;
    int n;

    old_entry = fsnotify_find_inode_mark(audit_tree_group, inode);
    if (!old_entry)
        return create_chunk(inode, tree);

    old = container_of(old_entry, struct audit_chunk, mark);

    /* are we already there? */
    spin_lock(&hash_lock);
    for (n = 0; n < old->count; n++) {
        if (old->owners[n].owner == tree) {
            spin_unlock(&hash_lock);
            fsnotify_put_mark(old_entry);
            return 0;
        }
    }
    spin_unlock(&hash_lock);

    chunk = alloc_chunk(old->count + 1);
    if (!chunk) {
        fsnotify_put_mark(old_entry);
        return -ENOMEM;
    }

    chunk_entry = &chunk->mark;

    spin_lock(&old_entry->lock);
    if (!old_entry->i.inode) {
        /* old_entry is being shot, lets just lie */
        spin_unlock(&old_entry->lock);
        fsnotify_put_mark(old_entry);
        free_chunk(chunk);
        return -ENOENT;
    }

    fsnotify_duplicate_mark(chunk_entry, old_entry);
    if (fsnotify_add_mark(chunk_entry, chunk_entry->group, chunk_entry->i.inode, NULL, 1)) {
        spin_unlock(&old_entry->lock);
        fsnotify_put_mark(chunk_entry);
        fsnotify_put_mark(old_entry);
        return -ENOSPC;
    }

    /* even though we hold old_entry->lock, this is safe since chunk_entry->lock could NEVER have been grabbed before */
    spin_lock(&chunk_entry->lock);
    spin_lock(&hash_lock);

    /* we now hold old_entry->lock, chunk_entry->lock, and hash_lock */
    if (tree->goner) {
        spin_unlock(&hash_lock);
        chunk->dead = 1;
        spin_unlock(&chunk_entry->lock);
        spin_unlock(&old_entry->lock);

        fsnotify_destroy_mark(chunk_entry);

        fsnotify_put_mark(chunk_entry);
        fsnotify_put_mark(old_entry);
        return 0;
    }
    list_replace_init(&old->trees, &chunk->trees);
    for (n = 0, p = chunk->owners; n < old->count; n++, p++) {
        struct audit_tree *s = old->owners[n].owner;
        p->owner = s;
        p->index = old->owners[n].index;
        if (!s) /* result of fallback in untag */
            continue;
        get_tree(s);
        list_replace_init(&old->owners[n].list, &p->list);
    }
    p->index = (chunk->count - 1) | (1U<<31);
    p->owner = tree;
    get_tree(tree);
    list_add(&p->list, &tree->chunks);
    list_replace_rcu(&old->hash, &chunk->hash);
    list_for_each_entry(owner, &chunk->trees, same_root)
        owner->root = chunk;
    old->dead = 1;
    if (!tree->root) {
        tree->root = chunk;
        list_add(&tree->same_root, &chunk->trees);
    }
    spin_unlock(&hash_lock);
    spin_unlock(&chunk_entry->lock);
    spin_unlock(&old_entry->lock);
    fsnotify_destroy_mark(old_entry);
    fsnotify_put_mark(chunk_entry); /* drop initial reference */
    fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
    return 0;
}

static void kill_rules(struct audit_tree *tree)
{
    struct audit_krule *rule, *next;
    struct audit_entry *entry;
    struct audit_buffer *ab;

    list_for_each_entry_safe(rule, next, &tree->rules, rlist) {
        entry = container_of(rule, struct audit_entry, rule);

        list_del_init(&rule->rlist);
        if (rule->tree) {
            /* not a half-baked one */
            ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
            audit_log_format(ab, "op=");
            audit_log_string(ab, "remove rule");
            audit_log_format(ab, " dir=");
            audit_log_untrustedstring(ab, rule->tree->pathname);
            audit_log_key(ab, rule->filterkey);
            audit_log_format(ab, " list=%d res=1", rule->listnr);
            audit_log_end(ab);
            rule->tree = NULL;
            list_del_rcu(&entry->list);
            list_del(&entry->rule.list);
            call_rcu(&entry->rcu, audit_free_rule_rcu);
        }
    }
}

/*
 * finish killing struct audit_tree
 */
static void prune_one(struct audit_tree *victim)
{
    spin_lock(&hash_lock);
    while (!list_empty(&victim->chunks)) {
        struct node *p;

        p = list_entry(victim->chunks.next, struct node, list);

        untag_chunk(p);
    }
    spin_unlock(&hash_lock);
    put_tree(victim);
}

/* trim the uncommitted chunks from tree */

static void trim_marked(struct audit_tree *tree)
{
    struct list_head *p, *q;
    spin_lock(&hash_lock);
    if (tree->goner) {
        spin_unlock(&hash_lock);
        return;
    }
    /* reorder */
    for (p = tree->chunks.next; p != &tree->chunks; p = q) {
        struct node *node = list_entry(p, struct node, list);
        q = p->next;
        if (node->index & (1U<<31)) {
            list_del_init(p);
            list_add(p, &tree->chunks);
        }
    }

    while (!list_empty(&tree->chunks)) {
        struct node *node;

        node = list_entry(tree->chunks.next, struct node, list);

        /* have we run out of marked? */
        if (!(node->index & (1U<<31)))
            break;

        untag_chunk(node);
    }
    if (!tree->root && !tree->goner) {
        tree->goner = 1;
        spin_unlock(&hash_lock);
        mutex_lock(&audit_filter_mutex);
        kill_rules(tree);
        list_del_init(&tree->list);
        mutex_unlock(&audit_filter_mutex);
        prune_one(tree);
    } else {
        spin_unlock(&hash_lock);
    }
}

static void audit_schedule_prune(void);

/* called with audit_filter_mutex */
int audit_remove_tree_rule(struct audit_krule *rule)
{
    struct audit_tree *tree;
    tree = rule->tree;
    if (tree) {
        spin_lock(&hash_lock);
        list_del_init(&rule->rlist);
        if (list_empty(&tree->rules) && !tree->goner) {
            tree->root = NULL;
            list_del_init(&tree->same_root);
            tree->goner = 1;
            list_move(&tree->list, &prune_list);
            rule->tree = NULL;
            spin_unlock(&hash_lock);
            audit_schedule_prune();
            return 1;
        }
        rule->tree = NULL;
        spin_unlock(&hash_lock);
        return 1;
    }
    return 0;
}

static int compare_root(struct vfsmount *mnt, void *arg)
{
    return mnt->mnt_root->d_inode == arg;
}

void audit_trim_trees(void)
{
    struct list_head cursor;

    mutex_lock(&audit_filter_mutex);
    list_add(&cursor, &tree_list);
    while (cursor.next != &tree_list) {
        struct audit_tree *tree;
        struct path path;
        struct vfsmount *root_mnt;
        struct node *node;
        int err;

        tree = container_of(cursor.next, struct audit_tree, list);
        get_tree(tree);
        list_del(&cursor);
        list_add(&cursor, &tree->list);
        mutex_unlock(&audit_filter_mutex);

        err = kern_path(tree->pathname, 0, &path);
        if (err)
            goto skip_it;

        root_mnt = collect_mounts(&path);
        path_put(&path);
        if (IS_ERR(root_mnt))
            goto skip_it;

        spin_lock(&hash_lock);
        list_for_each_entry(node, &tree->chunks, list) {
            struct audit_chunk *chunk = find_chunk(node);
            /* this could be NULL if the watch is dying else where... */
            struct inode *inode = chunk->mark.i.inode;
            node->index |= 1U<<31;
            if (iterate_mounts(compare_root, inode, root_mnt))
                node->index &= ~(1U<<31);
        }
        spin_unlock(&hash_lock);
        trim_marked(tree);
        put_tree(tree);
        drop_collected_mounts(root_mnt);
skip_it:
        mutex_lock(&audit_filter_mutex);
    }
    list_del(&cursor);
    mutex_unlock(&audit_filter_mutex);
}

int audit_make_tree(struct audit_krule *rule, char *pathname, u32 op)
{

    if (pathname[0] != '/' ||
        rule->listnr != AUDIT_FILTER_EXIT ||
        op != Audit_equal ||
        rule->inode_f || rule->watch || rule->tree)
        return -EINVAL;
    rule->tree = alloc_tree(pathname);
    if (!rule->tree)
        return -ENOMEM;
    return 0;
}

void audit_put_tree(struct audit_tree *tree)
{
    put_tree(tree);
}

static int tag_mount(struct vfsmount *mnt, void *arg)
{
    return tag_chunk(mnt->mnt_root->d_inode, arg);
}

/* called with audit_filter_mutex */
int audit_add_tree_rule(struct audit_krule *rule)
{
    struct audit_tree *seed = rule->tree, *tree;
    struct path path;
    struct vfsmount *mnt;
    int err;

    list_for_each_entry(tree, &tree_list, list) {
        if (!strcmp(seed->pathname, tree->pathname)) {
            put_tree(seed);
            rule->tree = tree;
            list_add(&rule->rlist, &tree->rules);
            return 0;
        }
    }
    tree = seed;
    list_add(&tree->list, &tree_list);
    list_add(&rule->rlist, &tree->rules);
    /* do not set rule->tree yet */
    mutex_unlock(&audit_filter_mutex);

    err = kern_path(tree->pathname, 0, &path);
    if (err)
        goto Err;
    mnt = collect_mounts(&path);
    path_put(&path);
    if (IS_ERR(mnt)) {
        err = PTR_ERR(mnt);
        goto Err;
    }

    get_tree(tree);
    err = iterate_mounts(tag_mount, tree, mnt);
    drop_collected_mounts(mnt);

    if (!err) {
        struct node *node;
        spin_lock(&hash_lock);
        list_for_each_entry(node, &tree->chunks, list)
            node->index &= ~(1U<<31);
        spin_unlock(&hash_lock);
    } else {
        trim_marked(tree);
        goto Err;
    }

    mutex_lock(&audit_filter_mutex);
    if (list_empty(&rule->rlist)) {
        put_tree(tree);
        return -ENOENT;
    }
    rule->tree = tree;
    put_tree(tree);

    return 0;
Err:
    mutex_lock(&audit_filter_mutex);
    list_del_init(&tree->list);
    list_del_init(&tree->rules);
    put_tree(tree);
    return err;
}

int audit_tag_tree(char *old, char *new)
{
    struct list_head cursor, barrier;
    int failed = 0;
    struct path path1, path2;
    struct vfsmount *tagged;
    int err;

    err = kern_path(new, 0, &path2);
    if (err)
        return err;
    tagged = collect_mounts(&path2);
    path_put(&path2);
    if (IS_ERR(tagged))
        return PTR_ERR(tagged);

    err = kern_path(old, 0, &path1);
    if (err) {
        drop_collected_mounts(tagged);
        return err;
    }

    mutex_lock(&audit_filter_mutex);
    list_add(&barrier, &tree_list);
    list_add(&cursor, &barrier);

    while (cursor.next != &tree_list) {
        struct audit_tree *tree;
        int good_one = 0;

        tree = container_of(cursor.next, struct audit_tree, list);
        get_tree(tree);
        list_del(&cursor);
        list_add(&cursor, &tree->list);
        mutex_unlock(&audit_filter_mutex);

        err = kern_path(tree->pathname, 0, &path2);
        if (!err) {
            good_one = path_is_under(&path1, &path2);
            path_put(&path2);
        }

        if (!good_one) {
            put_tree(tree);
            mutex_lock(&audit_filter_mutex);
            continue;
        }

        failed = iterate_mounts(tag_mount, tree, tagged);
        if (failed) {
            put_tree(tree);
            mutex_lock(&audit_filter_mutex);
            break;
        }

        mutex_lock(&audit_filter_mutex);
        spin_lock(&hash_lock);
        if (!tree->goner) {
            list_del(&tree->list);
            list_add(&tree->list, &tree_list);
        }
        spin_unlock(&hash_lock);
        put_tree(tree);
    }

    while (barrier.prev != &tree_list) {
        struct audit_tree *tree;

        tree = container_of(barrier.prev, struct audit_tree, list);
        get_tree(tree);
        list_del(&tree->list);
        list_add(&tree->list, &barrier);
        mutex_unlock(&audit_filter_mutex);

        if (!failed) {
            struct node *node;
            spin_lock(&hash_lock);
            list_for_each_entry(node, &tree->chunks, list)
                node->index &= ~(1U<<31);
            spin_unlock(&hash_lock);
        } else {
            trim_marked(tree);
        }

        put_tree(tree);
        mutex_lock(&audit_filter_mutex);
    }
    list_del(&barrier);
    list_del(&cursor);
    mutex_unlock(&audit_filter_mutex);
    path_put(&path1);
    drop_collected_mounts(tagged);
    return failed;
}

/*
 * That gets run when evict_chunk() ends up needing to kill audit_tree.
 * Runs from a separate thread.
 */
static int prune_tree_thread(void *unused)
{
    mutex_lock(&audit_cmd_mutex);
    mutex_lock(&audit_filter_mutex);

    while (!list_empty(&prune_list)) {
        struct audit_tree *victim;

        victim = list_entry(prune_list.next, struct audit_tree, list);
        list_del_init(&victim->list);

        mutex_unlock(&audit_filter_mutex);

        prune_one(victim);

        mutex_lock(&audit_filter_mutex);
    }

    mutex_unlock(&audit_filter_mutex);
    mutex_unlock(&audit_cmd_mutex);
    return 0;
}

static void audit_schedule_prune(void)
{
    kthread_run(prune_tree_thread, NULL, "audit_prune_tree");
}

/*
 * ... and that one is done if evict_chunk() decides to delay until the end
 * of syscall.  Runs synchronously.
 */
void audit_kill_trees(struct list_head *list)
{
    mutex_lock(&audit_cmd_mutex);
    mutex_lock(&audit_filter_mutex);

    while (!list_empty(list)) {
        struct audit_tree *victim;

        victim = list_entry(list->next, struct audit_tree, list);
        kill_rules(victim);
        list_del_init(&victim->list);

        mutex_unlock(&audit_filter_mutex);

        prune_one(victim);

        mutex_lock(&audit_filter_mutex);
    }

    mutex_unlock(&audit_filter_mutex);
    mutex_unlock(&audit_cmd_mutex);
}

/*
 *  Here comes the stuff asynchronous to auditctl operations
 */

static void evict_chunk(struct audit_chunk *chunk)
{
    struct audit_tree *owner;
    struct list_head *postponed = audit_killed_trees();
    int need_prune = 0;
    int n;

    if (chunk->dead)
        return;

    chunk->dead = 1;
    mutex_lock(&audit_filter_mutex);
    spin_lock(&hash_lock);
    while (!list_empty(&chunk->trees)) {
        owner = list_entry(chunk->trees.next,
                   struct audit_tree, same_root);
        owner->goner = 1;
        owner->root = NULL;
        list_del_init(&owner->same_root);
        spin_unlock(&hash_lock);
        if (!postponed) {
            kill_rules(owner);
            list_move(&owner->list, &prune_list);
            need_prune = 1;
        } else {
            list_move(&owner->list, postponed);
        }
        spin_lock(&hash_lock);
    }
    list_del_rcu(&chunk->hash);
    for (n = 0; n < chunk->count; n++)
        list_del_init(&chunk->owners[n].list);
    spin_unlock(&hash_lock);
    if (need_prune)
        audit_schedule_prune();
    mutex_unlock(&audit_filter_mutex);
}

static int audit_tree_handle_event(struct fsnotify_group *group,
                   struct fsnotify_mark *inode_mark,
                   struct fsnotify_mark *vfsmonut_mark,
                   struct fsnotify_event *event)
{
    BUG();
    return -EOPNOTSUPP;
}

static void audit_tree_freeing_mark(struct fsnotify_mark *entry, struct fsnotify_group *group)
{
    struct audit_chunk *chunk = container_of(entry, struct audit_chunk, mark);

    evict_chunk(chunk);

    /*
     * We are guaranteed to have at least one reference to the mark from
     * either the inode or the caller of fsnotify_destroy_mark().
     */
    BUG_ON(atomic_read(&entry->refcnt) < 1);
}

static bool audit_tree_send_event(struct fsnotify_group *group, struct inode *inode,
                  struct fsnotify_mark *inode_mark,
                  struct fsnotify_mark *vfsmount_mark,
                  __u32 mask, void *data, int data_type)
{
    return false;
}

static const struct fsnotify_ops audit_tree_ops = {
    .handle_event = audit_tree_handle_event,
    .should_send_event = audit_tree_send_event,
    .free_group_priv = NULL,
    .free_event_priv = NULL,
    .freeing_mark = audit_tree_freeing_mark,
};

static int __init audit_tree_init(void)
{
    int i;

    audit_tree_group = fsnotify_alloc_group(&audit_tree_ops);
    if (IS_ERR(audit_tree_group))
        audit_panic("cannot initialize fsnotify group for rectree watches");

    for (i = 0; i < HASH_SIZE; i++)
        INIT_LIST_HEAD(&chunk_hash_heads[i]);

    return 0;
}
__initcall(audit_tree_init);