linux-kernel - Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

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Message-Id: <E1GxVV8-0001Jz-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 21 Dec 2006 22:30:54 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	jengelh@...ux01.gwdg.de
CC:	rmk+lkml@....linux.org.uk, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all
 that again

> >
> >The root of the problem is that copy_to_user() may cause page faults
> >on the userspace buffer, and the page fault might (in case of a
> >maliciously crafted filesystem) recurse into the filesystem itself.
> 
> Would it be worthwhile to mlock the page? I know that needs root
> privs or some capability, but a static buffer could be put aside when
> fusermount is run.

And how would the kernel ensure, that the buffer supplied by userspace
is mlocked and stays mlocked during the memory copy?  I don't think
that would simplify the kerel side much, and would complicate the
userspace side considerably.

Miklos
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