From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sukadev Bhattiprolu Subject: Re: [RESEND PATCH] pid_ns: Fix proc_flush_task() accessing freed proc_mnt Date: Fri, 25 Jun 2010 14:26:18 -0700 Message-ID: <20100625212618.GA11917@us.ibm.com> References: <20100623203652.GA25298@redhat.com> <1277399329-18087-1-git-send-email-louis.rilling@kerlabs.com> <20100624191843.GA14205@redhat.com> <20100625102303.GG3773@hawkmoon.kerlabs.com> <20100625183733.GA2627@us.ibm.com> <20100625192945.GA25532@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20100625192945.GA25532@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Oleg Nesterov Cc: "Eric W. Biederman" , Pavel Emelyanov , Andrew Morton , Linux Containers , linux-kernel@vger.kernel.org List-Id: containers.vger.kernel.org Oleg Nesterov [oleg@redhat.com] wrote: | On 06/25, Sukadev Bhattiprolu wrote: | > | > Louis Rilling [Louis.Rilling@kerlabs.com] wrote: | > | - proc_pid_readdir(): | > | Needs similar check and protection to proc_pid_lookup(), but there is another | > | issue: next_tgid() can find a dying task: | > | > Hmm, I thought proc_pid_readdir() would be a problem too but convinced myself | > that it would not - since a process running proc_pid_readdir() would have | > a reference to the pid namespace, | | Where does this reference comes from ? Caller of proc_pid_readdir() would be living in the same pid namespace right ? i.e the pid namespace is not empty. If not they would be accessing a different instance of /proc -no ? Hmm, but thinking some more, if pid ns is created but /proc not remounted, the process would be accessing the parent ns (which cannot go away). A process cannot access a descendant/unrelated pid namespaces's /proc right ? | | proc_pid_readdir() pins the task_struct (ns->child_reaper), not the pid/ns. | | But I won't be surprised if I am wrong again ;) | | Oleg.