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audit: Make hash table insertion safe against concurrent lookups

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Currently, the audit tree code does not make sure that when a chunk is
inserted into the hash table, it is fully initialized. So in theory a
user of RCU lookup could see uninitialized structure in the hash table
and crash. Add appropriate barriers between initialization of the
structure and its insertion into hash table.

Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Jan Kara 2018-11-12 09:54:48 -05:00 committed by Paul Moore
parent 8d20d6e930
commit 1635e57223
1 changed files with 29 additions and 3 deletions
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32
kernel/audit_tree.c
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@ -186,6 +186,12 @@ static void insert_hash(struct audit_chunk *chunk)
if (!(chunk->mark.flags & FSNOTIFY_MARK_FLAG_ATTACHED))
return;
/*
* Make sure chunk is fully initialized before making it visible in the
* hash. Pairs with a data dependency barrier in READ_ONCE() in
* audit_tree_lookup().
*/
smp_wmb();
WARN_ON_ONCE(!chunk->key);
list = chunk_hash(chunk->key);
list_add_rcu(&chunk->hash, list);
@ -199,7 +205,11 @@ struct audit_chunk *audit_tree_lookup(const struct inode *inode)
struct audit_chunk *p;
list_for_each_entry_rcu(p, list, hash) {
if (p->key == key) {
/*
* We use a data dependency barrier in READ_ONCE() to make sure
* the chunk we see is fully initialized.
*/
if (READ_ONCE(p->key) == key) {
atomic_long_inc(&p->refs);
return p;
}
@ -304,9 +314,15 @@ static void untag_chunk(struct node *p)
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;
/*
* Make sure chunk is fully initialized before making it visible in the
* hash. Pairs with a data dependency barrier in READ_ONCE() in
* audit_tree_lookup().
*/
smp_wmb();
list_replace_rcu(&chunk->hash, &new->hash);
spin_unlock(&hash_lock);
fsnotify_detach_mark(entry);
mutex_unlock(&entry->group->mark_mutex);
@ -368,6 +384,10 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
list_add(&tree->same_root, &chunk->trees);
}
chunk->key = inode_to_key(inode);
/*
* Inserting into the hash table has to go last as once we do that RCU
* readers can see the chunk.
*/
insert_hash(chunk);
spin_unlock(&hash_lock);
mutex_unlock(&audit_tree_group->mark_mutex);
@ -459,7 +479,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
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;
@ -467,6 +486,13 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
tree->root = chunk;
list_add(&tree->same_root, &chunk->trees);
}
/*
* Make sure chunk is fully initialized before making it visible in the
* hash. Pairs with a data dependency barrier in READ_ONCE() in
* audit_tree_lookup().
*/
smp_wmb();
list_replace_rcu(&old->hash, &chunk->hash);
spin_unlock(&hash_lock);
fsnotify_detach_mark(old_entry);
mutex_unlock(&audit_tree_group->mark_mutex);