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

From: Al Viro
Date: Tue May 16 2017 - 14:48:29 EST

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.