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

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Message-ID: <1865922a0711060423ue81dbdct413b993e727f6f9@mail.gmail.com>
Date:	Tue, 6 Nov 2007 14:23:36 +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

On 11/6/07, Adrian Bunk <bunk@...nel.org> wrote:
> 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.
>

I admit I'm not experienced in such encoding stuff, but shouldn't the
ASCII and the ASCII-compatible UTF-8 encodings be enough for the
labels ?

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

Won't this complicate the code too much ?

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