On Fri, Nov 23, 2018 at 03:56:33PM +0800, Pan Bian wrote: > The function dentry_connected calls dput(dentry) to drop the previously > acquired reference to dentry. In this case, dentry can be released. > After that, IS_ROOT(dentry) checks the condition > (dentry == dentry->d_parent), which may result in a use-after-free bug. > This patch directly compares dentry with its parent obtained before > dropping the reference.
It's a bit more subtle than the description implies (the race has dentry connected during dget_parent() and the child we'd reached it through moved elsewhere during the dput()), but you are right - the race is there and that patch fixes it. I wonder if we could avoid those dget_parent()/dput() completely - looks like we might be able to with rcu_read_lock() and some care. OTOH, that's not going to be a hot path, anyway... Applied.
