linux-kernel - Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE

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Message-ID: <alpine.DEB.1.10.0906031542180.20254@gentwo.org>
Date:	Wed, 3 Jun 2009 15:45:57 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Larry H." <research@...reption.com>, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	pageexec@...email.hu
Subject: Re: Security fix for remapping of page 0 (was [PATCH] Change
 ZERO_SIZE_PTR to point at unmapped space)

On Wed, 3 Jun 2009, Alan Cox wrote:

> This appears to break the security models as they can no longer replace
> the CAP_SYS_RAWIO check with something based on the security model.

Right it would be fixed like CAP_SYS_NICE.

>
> > @@ -1043,6 +1046,9 @@ unsigned long do_mmap_pgoff(struct file
> >  		}
> >  	}
> >
> > +	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
> > +		return -EACCES;
> > +
>
> You can't move this bit here

The same code is executed in security_file_mmap right now which is the
next function called at this spot.

> >  	error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
>
> You need it in the default (no security) version of security_file_mmap()
> in security.h not hard coded into do_mmap_pgoff, and leave the one in
> cap_* alone.

But that would still leave it up to the security "models" to check
for basic security issues.

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