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Re: [RFA/PATCH] Fix recognition of NT_PRXFREG notes


On Mon, Jul 08, 2002 at 11:49:31PM +0200, Mark Kettenis wrote:
>    Date: Fri, 5 Jul 2002 11:00:29 +0930
>    From: Alan Modra <amodra@bigpond.net.au>
> 
>    On Thu, Jul 04, 2002 at 05:03:22PM +0200, Mark Kettenis wrote:
>    > Index: elf.c
>    > ===================================================================
>    > RCS file: /cvs/src/src/bfd/elf.c,v
>    > retrieving revision 1.152
>    > diff -u -p -r1.152 elf.c
>    > --- elf.c 4 Jul 2002 13:26:30 -0000 1.152
>    > +++ elf.c 4 Jul 2002 14:54:36 -0000
>    > @@ -6718,8 +6718,7 @@ elfcore_grok_note (abfd, note)
>    >  #endif
>    >  
>    >      case NT_PRXFPREG:		/* Linux SSE extension */
>    > -      if (note->namesz == 5
>    > -	  && ! strcmp (note->namedata, "LINUX"))
>    > +      if (strncmp (note->namedata, "LINUX", 5) == 0)
>    >  	return elfcore_grok_prxfpreg (abfd, note);
>    >        else
>    >  	return true;
> 
>    Don't the alignment rules require that the name be padded out to a
>    multiple of 4 chars? (or 8 on 64 bit ELF files).  So you should have
>    'L','I','N','U','X','\0','\0','\0' and thus can use strcmp.  Also,
>    it's a good idea to check namesz before accessing namedata.  I'm
>    sure I can make your strncmp segfault by carefully crafting a
>    non-compliant note.
> 
> Hmm, I modelled my code after the bits that check for "NetBSD-CORE"
> notes.  Therefore I'm pretty sure you won't crash on *my* strncmp ;-).

That sounds like a challenge.

notesz	4			yes, no string terminator
descsz	0
type	NT_PRXFPREG
name	'L', 'I', 'N', 'U'

I reckon your strncmp will run off the end of this note, possibly
crashing.

> That said, the current code isn't really robust.  There is no place
> where we check wheter namesz and descsz actually make any sense.  This

Yup.

>       if (note->namesz == 6
>           && strcmp (note->namedata, "LINUX") == 0)

OK.

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre


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