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

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Date:	Wed, 11 Jul 2012 02:36:39 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [ 26/48] udf: Avoid run away loop when partition table length
 is corrupted

On Tue, 2012-07-10 at 18:04 +0200, Jan Kara wrote:
> 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?

It's the sort of thing that I would expect to go into distribution
security updates a.s.a.p.  I don't see why it should wait that long
(though of course the merge window isn't *that* far away).

Ben.

-- 
Ben Hutchings
The generation of random numbers is too important to be left to chance.
                                                            - Robert Coveyou

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