linux-kernel - Re: [Patch] Fix Buffer overflow in hfsplus with a corrupted image

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Message-ID: <84144f020808240814l41be03a6x53d4c521d7d95eb6@mail.gmail.com>
Date:	Sun, 24 Aug 2008 18:14:47 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Eric Sesterhenn" <snakebyte@....de>
Cc:	zippel@...ux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch] Fix Buffer overflow in hfsplus with a corrupted image

Hi Eric,

On Sun, Aug 24, 2008 at 4:07 PM, Eric Sesterhenn <snakebyte@....de> wrote:
> when an hfsplus image gets corrupted it might happen that the catalog
> namelength field gets b0rked. If we mount such an image
> the memcpy() in hfsplus_cat_build_key_uni() writes more than the 255
> that fit in the name field. Depending on the size of the overwritten
> data, we either only get memory corruption or also trigger an oops like
> this:
>
> --- linux/fs/hfsplus/catalog.c.orig     2008-08-24 14:52:03.000000000 +0200
> +++ linux/fs/hfsplus/catalog.c  2008-08-24 14:54:15.000000000 +0200
> @@ -168,6 +168,11 @@ int hfsplus_find_cat(struct super_block
>                return -EIO;
>        }
>
> +       if (be16_to_cpu(tmp.thread.nodeName.length) >= 127) {
> +               printk(KERN_ERR "hfs: catalog name length corrupted\n");
> +               return -EIO;
> +       }

So, where does this 127 come from? I can only find reference to a
maximum length of 255 unicode characters (16 bits per character) in
the following technical note for HFS+ (see sections "HFS Plus Names"
and "Catalog Thread Records"):

  http://developer.apple.com/technotes/tn/tn1150.html

Hmm?

                        Pekka
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