Re: [PATCH] xfs: add a few more verifier tests

Dave Chinner
2014-08-19T22:38:56Z

On Tue, Aug 19, 2014 at 02:07:39PM -0500, Eric Sandeen wrote:
> On 8/19/14, 1:15 PM, Christoph Hellwig wrote:
> >> Anyway - bounds checking when we read from disk is a good thing!
> >
> > Absolutelt!
> >
> > Looks good modulo a few nitpicks below.
> >
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> >
> >> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> >> index 4bffffe..a4a9e0e 100644
> >> --- a/fs/xfs/libxfs/xfs_alloc.c
> >> +++ b/fs/xfs/libxfs/xfs_alloc.c
> >> @@ -2209,6 +2209,10 @@ xfs_agf_verify(
> >> be32_to_cpu(agf->agf_flcount) <= XFS_AGFL_SIZE(mp)))
> >> return false;
> >>
> >> + if (!(be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) <= XFS_BTREE_MAXLEVELS &&
> >> + be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) <= XFS_BTREE_MAXLEVELS))
> >> + return false;
> >
> > Maybe it's just me, but negated numeric comparisms always confuse the
> > hell out of me, why not simply:
> >
> > if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS)
> > return false;
> > if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) > XFS_BTREE_MAXLEVELS)
> > return false;
> >
> >> --- a/fs/xfs/libxfs/xfs_ialloc.c
> >> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> >> @@ -2051,6 +2051,8 @@ xfs_agi_verify(
> >> if (!XFS_AGI_GOOD_VERSION(be32_to_cpu(agi->agi_versionnum)))
> >> return false;
> >>
> >> + if (!(be32_to_cpu(agi->agi_level) <= XFS_BTREE_MAXLEVELS))
> >> + return false;
> >
> > Same here.
>
> yeah; just following the style of the functions as they exist today...
>
> if (!(agf->agf_magicnum == cpu_to_be32(XFS_AGF_MAGIC) &&
> XFS_AGF_GOOD_VERSION(be32_to_cpu(agf->agf_versionnum)) &&
> be32_to_cpu(agf->agf_freeblks) <= be32_to_cpu(agf->agf_length) &&
> ...
>
> dunno. Don't care too much either way, but consistency and all that...

I prefer the metho Christoph suggested - most of the verifiers use
that "single check per if statement" pattern because it makes the
checks being performed so much easier to read.

> Maybe the "AGF_GOOD_VERSION" required the negation, and it all got lumped
> together?

Those should probably be cleaned up - they were done like that
originally as a direct transcript from pre-existing code checks
to simplify review, not because it was "nice" code.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com