linux-kernel - Re: fs: hfs: Possible issue with increment of extent

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Message-ID: <7036d8c5-92cb-257b-848a-33e0ba5829e5@canonical.com>
Date:   Fri, 31 Aug 2018 14:56:46 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: fs: hfs: Possible issue with increment of extent

On 31/08/18 14:56, Al Viro wrote:
> 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@...l.org>
> Date:   Wed Feb 25 16:17:36 2004 -0800
> 
>     [PATCH] HFS rewrite
>     
>     From: Roman Zippel <zippel@...ux-m68k.org>
> 
> and it's almost certainly a bug in there, judging by the code nearby...
> 
OK, I'll send a fix then.

Colin