linux-kernel - Re: [PATCH][RFC] HPFS: Don't use pointer to out-of-scope array

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Message-ID: <alpine.LNX.2.00.1103212128350.15815@swampdragon.chaosbits.net>
Date:	Mon, 21 Mar 2011 21:28:41 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Andreas Schwab <schwab@...ux-m68k.org>
cc:	linux-kernel@...r.kernel.org,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Subject: Re: [PATCH][RFC] HPFS: Don't use pointer to out-of-scope array

On Thu, 6 Jan 2011, Jesper Juhl wrote:

> On Fri, 24 Dec 2010, Jesper Juhl wrote:
> 
> > On Fri, 24 Dec 2010, Andreas Schwab wrote:
> > 
> > > Jesper Juhl <jj@...osbits.net> writes:
> > > 
> > > > Secondly I fail to see how this code inside the while loop can even work:
> > > >
> > > >   if (hpfs_ea_read(s, a, ano, pos + 4, ea->namelen + 1 + (ea->indirect ? 8 : 0), ex + 4))
> > > >
> > > > There is nothing initializing 'ex' which 'ea' points to, so 
> > > > 'ea->namelen' and 'ea->indirect' are uninitialized.
> > > 
> > > The preceding hpfs_ea_read should do it (it reads the first 4 bytes of
> > > ex which aliases ea->namelen and ea->indirect).
> > > 
> > How I managed to miss that I don't know, but I did and you are correct. 
> > Thanks.
> > 
> But, this bit: "in the 'while (pos < len)' loop a local char array 'ex' is 
> defined and subsequently the pointer variable 'ea' is set to point to the 
> array. Inside the loop we may jump to the 'indirect' label which is 
> outside the loop scope. At the 'indirect' label 'ea' (which now points 
> to a array that is no longer in scope) is dereferenced - that's not good. 
> The patch below addresses that problem by moving the 'ex' array out of 
> the loop scope and into function scope."
> I still believe to be correct and that's what the patch actually 
> addresses, so can we agree that the patch makes sense and should be 
> merged?
> 
Ping? 

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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