linux-kernel - Re: [PATCH 1/2] prctl: take mmap sem for writing to protect against others

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Message-ID: <CAKeScWgfg2G6q7ffBLGi2R_xHcp+8NbYEQ7t73pY9oDKWgeqog@mail.gmail.com>
Date:	Wed, 6 Jan 2016 15:05:09 +0530
From:	Anshuman Khandual <anshuman.linux@...il.com>
To:	Mateusz Guzik <mguzik@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Jarod Wilson <jarod@...hat.com>,
	Jan Stancek <jstancek@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/2] prctl: take mmap sem for writing to protect against others

On Wed, Jan 6, 2016 at 10:32 AM, Mateusz Guzik <mguzik@...hat.com> wrote:
> The code was taking the semaphore for reading, which does not protect
> against readers nor concurrent modifications.

(down/up)_read does not protect against concurrent readers ?

>
> The problem could cause a sanity checks to fail in procfs's cmdline
> reader, resulting in an OOPS.
>

Can you explain this a bit and may be give some examples ?

> Note that some functions perform an unlocked read of various mm fields,
> but they seem to be fine despite possible modificaton.

Those need to be fixed as well ?

> Signed-off-by: Mateusz Guzik <mguzik@...hat.com>
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