linux-kernel - Re: [PATCH] [iov_iter] use memmove() when copying to/from user page

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Message-ID: <20170516213347.GT390@ZenIV.linux.org.uk>
Date:   Tue, 16 May 2017 22:33:48 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [iov_iter] use memmove() when copying to/from user page

On Tue, May 16, 2017 at 02:01:51PM -0700, Dmitry Vyukov wrote:

> > In that case your patch does not suffice.  Overlapping move _forwards_ still
> > yields unexpected results, doesn't it?
> 
> Why? memmove can move both ways. Do we need to change more memcpy's to
> memmove's?

Because it's not going to be *one* call of memcpy() or memmove().  It's
one per page.