linux-kernel - Re: [PACTH v3 1/3] mm, proc: Implement /proc/<pid>/totmaps

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Message-ID: <20160816184733.GA19380@pc.thejh.net>
Date:	Tue, 16 Aug 2016 20:47:33 +0200
From:	Jann Horn <jann@...jh.net>
To:	Robert Foss <robert.foss@...labora.com>
Cc:	corbet@....net, akpm@...ux-foundation.org, vbabka@...e.cz,
	mhocko@...e.com, koct9i@...il.com, hughd@...gle.com,
	n-horiguchi@...jp.nec.com, john.stultz@...aro.org,
	minchan@...nel.org, ross.zwisler@...ux.intel.com,
	jmarchan@...hat.com, hannes@...xchg.org, mingo@...nel.org,
	keescook@...omium.org, viro@...iv.linux.org.uk,
	gorcunov@...nvz.org, sonnyrao@...omium.org,
	plaguedbypenguins@...il.com, eric.engestrom@...tec.com,
	rientjes@...gle.com, jdanis@...gle.com, calvinowens@...com,
	adobriyan@...il.com, kirill.shutemov@...ux.intel.com,
	ldufour@...ux.vnet.ibm.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Ben Zhang <benzh@...omium.org>,
	Bryan Freed <bfreed@...omium.org>,
	Filipe Brandenburger <filbranden@...omium.org>,
	Mateusz Guzik <mguzik@...hat.com>,
	Michal Hocko <mhocko@...nel.org>, linux-api@...r.kernel.org
Subject: Re: [PACTH v3 1/3] mm, proc: Implement /proc/<pid>/totmaps

On Tue, Aug 16, 2016 at 02:34:15PM -0400, Robert Foss wrote:
> On 2016-08-16 02:18 PM, Jann Horn wrote:
> >On Tue, Aug 16, 2016 at 01:34:14PM -0400, robert.foss@...labora.com wrote:
> >>+	}
> >>+
> >>+	return 0;
> >>+
> >>+error:
> >>+	return ret;
> >>+}
> >>+
> >[...]
> >>+const struct file_operations proc_totmaps_operations = {
> >>+	.open		= totmaps_open,
> >>+	.read		= seq_read,
> >>+	.llseek		= seq_lseek,
> >>+	.release	= proc_map_release,
> >>+};
> >
> >As I said regarding v2 already:
> >This won't release priv->task, causing a memory leak (exploitable
> >through a reference counter overflow of the task_struct usage
> >counter).
> 
> Sorry about dropping the ball on that one, what's correct way to release
> priv->task?

get_proc_task() does get_pid_task(), which does get_task_struct(), which
increments the ->usage field of the task. You want the inverse
operation - something that decrements ->usage and checks for zero. This is
done via put_task_struct(), which is defined a few lines below
get_task_struct().

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