On 10/25, Kees Cook wrote: > > On Thu, Oct 25, 2018 at 12:13 PM, Oleg Nesterov <o...@redhat.com> wrote: > > So again, suppose that "child" is already dead. Its task_struct can't be > > freed, > > but child->real_parent can point to the already freed memory. > > I can't find a path for "child" to be released. I see task_lock() > always called on it before it ends up in Yama.
Are you saying that yama_ptrace_access_check() is always called under task_lock(child) ? Yes, it seems so So what? Say, ptrace_attach() can hit a dead task. It should notice this and fail later, but security_ptrace_access_check() is called before that. > > This means that the 1st walker = rcu_dereference(walker->real_parent) is > > fine, > > this simply reads the child->real_parent pointer, but on the second > > iteration > > > > walker = rcu_dereference(walker->real_parent); > > > > reads the alredy freed memory. > > What does rcu_read_lock() protect actually protect here? I thought > none of the task structs would be freed until after all > rcu_read_unlock() finished. See another email I sent you a minute ago. Oleg.
