userns: prevent speculative execution

[mirror_ubuntu-artful-kernel.git] / kernel / audit_tree.c

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

struct audit_tree;
struct audit_chunk;

struct audit_tree {
        refcount_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);
static struct task_struct *prune_thread;

/*
 * 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) {
                refcount_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)
{
        refcount_inc(&tree->count);
}

static inline void put_tree(struct audit_tree *tree)
{
        if (refcount_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_group);
        chunk->mark.mask = FS_IN_IGNORED;
        return chunk;
}

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

/* Function to return search key in our hash from inode. */
static unsigned long inode_to_key(const struct inode *inode)
{
        return (unsigned long)inode;
}

/*
 * Function to return search key in our hash from chunk. Key 0 is special and
 * should never be present in the hash.
 */
static unsigned long chunk_to_key(struct audit_chunk *chunk)
{
        /*
         * We have a reference to the mark so it should be attached to a
         * connector.
         */
        if (WARN_ON_ONCE(!chunk->mark.connector))
                return 0;
        return (unsigned long)chunk->mark.connector->inode;
}

static inline struct list_head *chunk_hash(unsigned long key)
{
        unsigned long n = key / 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)
{
        unsigned long key = chunk_to_key(chunk);
        struct list_head *list;

        if (!(chunk->mark.flags & FSNOTIFY_MARK_FLAG_ATTACHED))
                return;
        list = chunk_hash(key);
        list_add_rcu(&chunk->hash, list);
}

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

        list_for_each_entry_rcu(p, list, hash) {
                if (chunk_to_key(p) == key) {
                        atomic_long_inc(&p->refs);
                        return p;
                }
        }
        return NULL;
}

bool 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 true;
        return false;
}

/* 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);

        mutex_lock(&entry->group->mark_mutex);
        spin_lock(&entry->lock);
        /*
         * mark_mutex protects mark from getting detached and thus also from
         * mark->connector->inode getting NULL.
         */
        if (chunk->dead || !(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
                spin_unlock(&entry->lock);
                mutex_unlock(&entry->group->mark_mutex);
                if (new)
                        fsnotify_put_mark(&new->mark);
                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);
                mutex_unlock(&entry->group->mark_mutex);
                fsnotify_destroy_mark(entry, audit_tree_group);
                goto out;
        }

        if (!new)
                goto Fallback;

        if (fsnotify_add_mark_locked(&new->mark, entry->connector->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);
        mutex_unlock(&entry->group->mark_mutex);
        fsnotify_destroy_mark(entry, audit_tree_group);
        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);
        mutex_unlock(&entry->group->mark_mutex);
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, 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, audit_tree_group);
                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_mark(&inode->i_fsnotify_marks,
                                       audit_tree_group);
        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;

        mutex_lock(&old_entry->group->mark_mutex);
        spin_lock(&old_entry->lock);
        /*
         * mark_mutex protects mark from getting detached and thus also from
         * mark->connector->inode getting NULL.
         */
        if (!(old_entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
                /* old_entry is being shot, lets just lie */
                spin_unlock(&old_entry->lock);
                mutex_unlock(&old_entry->group->mark_mutex);
                fsnotify_put_mark(old_entry);
                fsnotify_put_mark(&chunk->mark);
                return -ENOENT;
        }

        if (fsnotify_add_mark_locked(chunk_entry,
                             old_entry->connector->inode, NULL, 1)) {
                spin_unlock(&old_entry->lock);
                mutex_unlock(&old_entry->group->mark_mutex);
                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);
                mutex_unlock(&old_entry->group->mark_mutex);

                fsnotify_destroy_mark(chunk_entry, audit_tree_group);

                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);
        mutex_unlock(&old_entry->group->mark_mutex);
        fsnotify_destroy_mark(old_entry, audit_tree_group);
        fsnotify_put_mark(chunk_entry); /* drop initial reference */
        fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
        return 0;
}

static void audit_tree_log_remove_rule(struct audit_krule *rule)
{
        struct audit_buffer *ab;

        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
        if (unlikely(!ab))
                return;
        audit_log_format(ab, "op=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);
}

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

        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 */
                        audit_tree_log_remove_rule(rule);
                        if (entry->rule.exe)
                                audit_remove_mark(entry->rule.exe);
                        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 inode_to_key(d_backing_inode(mnt->mnt_root)) ==
               (unsigned long)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... */
                        node->index |= 1U<<31;
                        if (iterate_mounts(compare_root,
                                           (void *)chunk_to_key(chunk),
                                           root_mnt))
                                node->index &= ~(1U<<31);
                }
                spin_unlock(&hash_lock);
                trim_marked(tree);
                drop_collected_mounts(root_mnt);
skip_it:
                put_tree(tree);
                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(d_backing_inode(mnt->mnt_root), arg);
}

/*
 * 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)
{
        for (;;) {
                if (list_empty(&prune_list)) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        schedule();
                }

                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 int audit_launch_prune(void)
{
        if (prune_thread)
                return 0;
        prune_thread = kthread_run(prune_tree_thread, NULL,
                                "audit_prune_tree");
        if (IS_ERR(prune_thread)) {
                pr_err("cannot start thread audit_prune_tree");
                prune_thread = NULL;
                return -ENOMEM;
        }
        return 0;
}

/* 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;

        rule->tree = NULL;
        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);

        if (unlikely(!prune_thread)) {
                err = audit_launch_prune();
                if (err)
                        goto Err;
        }

        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;
}


static void audit_schedule_prune(void)
{
        wake_up_process(prune_thread);
}

/*
 * ... 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);
        mutex_unlock(&audit_filter_mutex);
        if (need_prune)
                audit_schedule_prune();
}

static int audit_tree_handle_event(struct fsnotify_group *group,
                                   struct inode *to_tell,
                                   struct fsnotify_mark *inode_mark,
                                   struct fsnotify_mark *vfsmount_mark,
                                   u32 mask, const void *data, int data_type,
                                   const unsigned char *file_name, u32 cookie,
                                   struct fsnotify_iter_info *iter_info)
{
        return 0;
}

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 const struct fsnotify_ops audit_tree_ops = {
        .handle_event = audit_tree_handle_event,
        .freeing_mark = audit_tree_freeing_mark,
        .free_mark = audit_tree_destroy_watch,
};

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);