linux-kernel - Re: [PATCH] user_ns: use correct check for single-threadedness

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Message-ID: <55B7C3AA.8070608@redhat.com>
Date:	Tue, 28 Jul 2015 14:02:18 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Kees Cook <keescook@...omium.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Oleg Nesterov <oleg@...hat.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Ricky Zhou <rickyz@...omium.org>,
	Julien Tinnes <jln@...gle.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness

On 07/28/2015 01:15 PM, Kees Cook wrote:
> From: Ricky Zhou <rickyz@...omium.org>
> 
> Checking mm_users > 1 does not mean a process is multithreaded. For
> example, reading /proc/PID/maps temporarily increments mm_users, allowing
> other processes to (accidentally) interfere with unshare() calls.
> 
> This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly
> returning EINVAL if another processes happened to be simultaneously
> reading the maps file.
> 
> Signed-off-by: Ricky Zhou <rickyz@...omium.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Cc: stable@...r.kernel.org

Reviewed-by: Rik van Riel <riel@...hat.com>

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