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Date: Wed, 15 Aug 2007 23:05:09 +0200 (CEST)
From: Wojciech Purczynski <>
To: Dan Yefimov <>
Subject: Re: COSEINC Linux Advisory #1: Linux Kernel Parent Process Death
 Signal Vulnerability

> > 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.

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