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

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Message-ID: <20170516184821.GQ390@ZenIV.linux.org.uk>
Date:   Tue, 16 May 2017 19:48:21 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     dvyukov@...gle.com, kcc@...gle.com, edumazet@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [iov_iter] use memmove() when copying to/from user page

On Tue, May 16, 2017 at 02:27:34PM +0200, Alexander Potapenko wrote:
> It's possible that calling sendfile() to copy the data from a memfd to
> itself may result in doing a memcpy() with overlapping arguments.
> To avoid undefined behavior here, replace memcpy() with memmove() and
> rename memcpy_to_page()/memcpy_from_page() accordingly.

Er...  And what semantics would you assign to such sendfile()?  I really
want to see details, because it sounds like memmove() here will not be
any more useful than memcpy() - you still can esily get odd behaviour.