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 18:04:52 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	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 Tue 10-07-12 16:52:26, Ben Hutchings wrote:
> 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)) {
  Yeah, thanks for spotting this! I've queued the attached patch. I don't
find this really pressing so I'll push it in the next merge window. OK?

								Honza

-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-udf-Improve-table-length-check-to-avoid-possible-ove.patch" of type "text/x-patch" (1290 bytes)