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Date:   Fri, 31 Aug 2018 14:56:15 +0100
From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     Colin Ian King <colin.king@canonical.com>
Cc:     linux-fsdevel@vger.kernel.org, David Howells <dhowells@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: fs: hfs: Possible issue with increment of extent
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On Fri, Aug 31, 2018 at 02:39:11PM +0100, Colin Ian King wrote:
> Hi,
> 
> Static analysis has picked up a potential issue with an out of bounds
> read in fs/hfs/extent.c; the following for-loop in  hfs_free_fork()
> increments i and also extent while also reading extent[i].count.  This
> looks incorrect to me, I think the increment of extent is not needed:
> 
>         for (i = 0; i < 3; extent++, i++)
>                 blocks += be16_to_cpu(extent[i].count);
> 
>         res = hfs_free_extents(sb, extent, blocks, blocks);
> 
> I'm not familiar enough with the code to conclude that removing the
> increment of extent is necessary a correct fix just in case I'm missing
> something subtle here.

Goes back to commit d1081202f1d0 (in bk-to-git historical tree)
Author: Andrew Morton <akpm@osdl.org>
Date:   Wed Feb 25 16:17:36 2004 -0800

    [PATCH] HFS rewrite
    
    From: Roman Zippel <zippel@linux-m68k.org>

and it's almost certainly a bug in there, judging by the code nearby...