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

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Date:	Fri, 25 Jun 2010 15:07:13 -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:
| >
| > 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 ?
| 
| Afaics, in general not.
| 
| Suppose that we do something like
| 
| 	if (!clone(CLONE_NEWPID)) {
| 		mount("none", "/SUB_PROC", "proc", 0, NULL);
| 		exit();
| 	}
| 
| After that /SUB_PROC/ still exists, one can do "ls /SUB_PROC/".

Yes, I see it now. Thanks,

Sukadev
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