Re: [PATCH 5/6] audit: Make hash table insertion safe against concurrent lookups

Currently, the audit tree code does not make sure that when a chunk in inserted into the hash table, it is fully initialized. So in theory (in practice only on DEC Alpha) 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. Signed-off-by: Jan Kara <jack(a)suse.cz&gt; --- kernel/audit_tree.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c index 89ad8857a578..46cc6d046c75 100644 --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -198,7 +198,11 @@ 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; } @@ -303,9 +307,15 @@ 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); @@ -367,6 +377,12 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree) list_add(&tree->same_root, &chunk->trees); } chunk->key = inode_to_key(inode); + /* + * 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(); insert_hash(chunk); spin_unlock(&hash_lock); mutex_unlock(&audit_tree_group->mark_mutex); @@ -458,7 +474,6 @@ 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; @@ -466,6 +481,13 @@ 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);