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From: Daniel Phillips <news-innominate.list.linux.kernel@innominate.de>
Reply-To: Daniel Phillips <phillips@innominate.de>
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Subject: Re: Modprobe local root exploit
Date: Tue, 14 Nov 2000 15:23:50 +0100
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        Peter Samuelson <peter@cadcamlab.org>
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On Tue, 14 Nov 2000, David Relson wrote:
> At 06:29 AM 11/14/00, Daniel Phillips wrote:
> 
> >Heading in the right direction, but this is equivalent to:
> >
> >   if (isalnum(*p) && *p != '-' && *p != '_') return -EINVAL;
> >
> >which is faster, smaller and easier to read.
> 
> Almost right, but you forgot to negate isalnum().  Should be:
> 
>          if (!isalnum(*p) && *p != '-' && *p != '_') return -EINVAL;
> 
> or
>          if (! (isalnum(*p) || *p == '-' || *p == '_')) return -EINVAL;
> 
> I think I prefer the older version with "continue" as I don't have to think 
> about all the negatives ("!"), i.e.
> 
>          for ( ... )
>          {
>                  if ( isalnum(*p) || *p == '-' || *p == '_' )
>                          continue;
>                  return -EINVAL;
>          }
> 

I reserve the right to make coding errors, thanks for not letting it get
written into history :-)

How about:

  for ( ... ) if (!isalnum(*p) && !strchr("-_", *p)) return -EINVAL;

-- 
Daniel
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