linux-kernel - Re: [PATCH] lib: introduce strdup_from

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Message-ID: <BANLkTimB2UanZA4wf=uBGcj=wKmDhCco=w@mail.gmail.com>
Date:	Fri, 3 Jun 2011 21:26:21 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Timur Tabi <timur@...escale.com>
Cc:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	scottwood@...escale.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] lib: introduce strdup_from_user

On Fri, Jun 3, 2011 at 9:22 PM, Timur Tabi <timur@...escale.com> wrote:
> Alexey Dobriyan wrote:
>> NAK
>> It accesses userspace data twice.
>
> What's wrong with that?

If mm is shared, data can or will change under you.

> How else is it supposed to know how much to allocate
> without using strlen first?

I don't know.
What I know is that your function doesn't guarantee NUL-termination.

> Besides, it was Alan's idea to make this a common function.  I can easily put it
> back in my driver.

Don't do that.
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