Re: [PATCH 4/6 v2] xfs: validate btree records on retreival

[Dave Chinner <david@fromorbit.com>]

On Tue, Jun 05, 2018 at 12:42:07PM +0200, Carlos Maiolino wrote:
> > +	if (irec->rc_blockcount == 0 || irec->rc_blockcount > MAXREFCEXTLEN)
> > +		goto out_bad_rec;
> > +
> > +	/* handle special COW-staging state */
> > +	realstart = irec->rc_startblock;
> > +	if (realstart & XFS_REFC_COW_START) {
> > +		if (irec->rc_refcount != 1)
> > +			goto out_bad_rec;
> > +		realstart &= ~XFS_REFC_COW_START;
> >  	}
> > -	return error;
> > +
> > +	/* check for valid extent range, including overflow */
> > +	if (!xfs_verify_agbno(mp, agno, realstart))
> > +		goto out_bad_rec;
> > +	if (realstart > realstart + irec->rc_blockcount)
> 
> I am not sure if I'm right, but I thought this ought to be ">="?

We've already caught zero length and block count greater than
2^32-1, so if the above is true we've wrapped through zero during
the addition. But we can never add 0 or 2^32 to realstart here, so
the "==" condition will not occur and we don't need to check for
it....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com