linux-kernel - Re: [RESEND PATCH] pid_ns: Fix proc_flush_task() accessing freed proc

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Date:	Fri, 25 Jun 2010 14:26:18 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] pid_ns: Fix proc_flush_task() accessing freed
	proc_mnt

Oleg Nesterov [oleg@...hat.com] wrote:
| On 06/25, Sukadev Bhattiprolu wrote:
| >
| > Louis Rilling [Louis.Rilling@...labs.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.
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