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

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Message-ID: <20071106114738.GH26163@stusta.de>
Date:	Tue, 6 Nov 2007 12:47:38 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
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

On Tue, Nov 06, 2007 at 01:34:05PM +0200, Ahmed S. Darwish wrote:
> 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 ?

It should work for all charsets you'll usually have to handle.

It would not work if someone would e.g. give you UTF-16 encoded strings, 
but I don't see this happening in practice.

> Regards,

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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