linux-kernel - Re: [ 26/48] udf: Avoid run away loop when partition table length is corrupted

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Date:	Tue, 10 Jul 2012 16:52:26 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Jan Kara <jack@...e.cz>
Subject: Re: [ 26/48] udf: Avoid run away loop when partition table length
 is corrupted

On Mon, Jul 09, 2012 at 03:31:42PM +0100, Ben Hutchings wrote:
> 3.2-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Jan Kara <jack@...e.cz>
> 
> commit adee11b2085bee90bd8f4f52123ffb07882d6256 upstream.
> 
> Check provided length of partition table so that (possibly maliciously)
> corrupted partition table cannot cause accessing data beyond current buffer.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> ---
>  fs/udf/super.c |   10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/udf/super.c b/fs/udf/super.c
> index 9da6f4e..ce911f5 100644
> --- a/fs/udf/super.c
> +++ b/fs/udf/super.c
[...]
> @@ -1232,13 +1233,20 @@ static int udf_load_logicalvol(struct super_block *sb, sector_t block,
>  		return 1;
>  	BUG_ON(ident != TAG_IDENT_LVD);
>  	lvd = (struct logicalVolDesc *)bh->b_data;
> +	table_len = le32_to_cpu(lvd->mapTableLength);
> +	if (sizeof(*lvd) + table_len > sb->s_blocksize) {
[...]

I don't think this is sufficient, unless there has been some prior
validation of lvd->mapTableLength.  On a 32-bit machine, the addition
may overflow.  The untrusted value has to be validated before doing
any arithmetic on it, e.g.:

	if (table_len > sb->s_blocksize - sizeof(*lv)) {

Ben.

-- 
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
                                                              - Albert Camus
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