> > In this case check_kill_permission() returns -EPERM for unprivileged > > parent. > > > You always talked about setuid root process sending PDEATH_SIG to the > root child, didn't you? check_kill_permission() checks current->euid and > current->uid against t->uid and t->suid, where 'current' is the pointer > to the task_struct of the sender, or, in our case, of the dying setuid > root process, and 't' is the pointer to the task_struct of the root > child. If one of those checks succeeds then the entire > check_kill_permission() succeeds. current->euid is in our case 0, t->uid > and t->suid are 0 too. So where is the problem? The problem is that without suid binary execved from parent process you can not send the signal. ;) With suid binary you can and that makes this issue a privilege escalation vulnerability.
