linux-kernel - Re: [PATCH] Smackv10: Smack rules grammar + their stateful parser

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Date:	Tue, 6 Nov 2007 13:34:05 +0200
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	Kyle Moffett <mrmacman_g4@....com>,
	Casey Schaufler <casey@...aufler-ca.com>, akpm@...l.org,
	torvalds@...l.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Smackv10: Smack rules grammar + their stateful parser

Hi,

On Tue, Nov 06, 2007 at 09:56:51AM +0100, Adrian Bunk wrote:
> On Tue, Nov 06, 2007 at 03:26:12AM -0500, Kyle Moffett wrote:
> > On Nov 06, 2007, at 01:33:05, Adrian Bunk wrote:
> >> Can you limit this to 7bit ASCII and use isascii() somewhere?
> >>
> >> Otherwise I'd expect funny things to happen when you e.g. use isspace() on 
> >> the UTF-8 encoded character ??.
> >
> > Actually, you don't need to.  You tell them it expects UTF-8 encoded 
> > strings and be done with it.  All US-ASCII characters from 0 through 127 
> > (IE: high bit clear) are exactly the same in UTF-8, and UTF-8 special 
> > characters have the high bit set in all bytes.  Therefore you just assume 
> > that anything with the high bit set is part of a word and you can handle 
> > basic UTF-8.  (It doesn't work on special UTF-8 space characters like 
> > nonbreaking space and similar, but handling those is significantly more 
> > complicated).
> 
> The documentations says:
> "Smack labels cannot contain unprintable characters or the "/" (slash) 
>  character."
> 
> What you propose might contain unprintable characters, and it might even 
> be invalid UTF-8.
> 

As far as I understand the problem now, isspace() accepts the 0xa0
character which might collide with some of UTF-8 encoded characters
cause the high bit is set.

I used "if (!isspace(c) && !isgraph(c)) return -EINVAL;" to test 
rules' characters validity which seems not enough. I'll add !isascii(c)
in the condition and ask Casey to change the documentation to be
something like:

Smack labels are represented in ASCII characters, they cannot contain
unprintable characters or the '/' (slash) character.

and in write():
if (!isascii(c) return -EINVAL;
if (!isspace(c) && !isgraph(c)) return -EINVAL;

This satisfy above customized labels rule, right ?

Regards,

--
Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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