Release 4.15 kernel/audit_tree.c

// SPDX-License-Identifier: GPL-2.0
#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;
}

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

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

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/* to avoid bringing the entire thing in audit.h */


const char *audit_tree_path(struct audit_tree *tree)
{
	return tree->pathname;
}

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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);
}

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

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

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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);
}

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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;
}

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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;
}

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/*
 * 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;
}

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

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/* 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);
}

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/* 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;
}

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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;
}

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/* 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]);
}

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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);
}

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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;
}

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/* 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;
}

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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);
}

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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);
		}
	}
}

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/*
 * 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);
}

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/* 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->