Re: [PATCH 04/10] audit: Embed key into chunk

Currently chunk hash key (which is in fact pointer to the inode) is derived as chunk->mark.conn->obj. It is tricky to make this dereference reliable for hash table lookups only under RCU as mark can get detached from the connector and connector gets freed independently of the running lookup. Thus there is a possible use after free / NULL ptr dereference issue: CPU1 CPU2 untag_chunk() ... audit_tree_lookup() list_for_each_entry_rcu(p, list, hash) { list_del_rcu(&chunk->hash); fsnotify_destroy_mark(entry); fsnotify_put_mark(entry) chunk_to_key(p) if (!chunk->mark.connector) ... hlist_del_init_rcu(&mark->obj_list); if (hlist_empty(&conn->list)) { inode = fsnotify_detach_connector_from_object(conn); mark->connector = NULL; ... frees connector from workqueue chunk->mark.connector->obj This race is probably impossible to hit in practice as the race window on CPU1 is very narrow and CPU2 has a lot of code to execute. Still it's better to have this fixed. Since the inode the chunk is attached to is constant during chunk's lifetime it is easy to cache the key in the chunk itself and thus avoid these issues. Signed-off-by: Jan Kara <jack(a)suse.cz&gt; --- kernel/audit_tree.c | 27 ++++++++------------------- 1 file changed, 8 insertions(+), 19 deletions(-)