Re: [PATCH 4/4] xfs_repair: don't corrupt a attr fork da3 node when clearing forw/back

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Feb 04, 2020 at 10:29:26PM -0700, Allison Collins wrote:
> 
> 
> On 2/4/20 5:46 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > In process_longform_attr, we enforce that the root block of the
> > attribute index must have both forw or back pointers set to zero.
> > Unfortunately, the code that nulls out the pointers is not aware that
> > the root block could be in da3 node format.
> > 
> > This leads to corruption of da3 root node blocks because the functions
> > that convert attr3 leaf headers to and from the ondisk structures
> > perform some interpretation of firstused on what they think is an attr1
> > leaf block.
> > 
> > Found by using xfs/402 to fuzz hdr.info.hdr.forw.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >   repair/attr_repair.c |  181 ++++++++++++++++++++++++++++++++------------------
> >   1 file changed, 117 insertions(+), 64 deletions(-)
> > 
> > 
> > diff --git a/repair/attr_repair.c b/repair/attr_repair.c
> > index 7b26df33..535fcfbb 100644
> > --- a/repair/attr_repair.c
> > +++ b/repair/attr_repair.c
> > @@ -952,6 +952,106 @@ _("wrong FS UUID, inode %" PRIu64 " attr block %" PRIu64 "\n"),
> >   	return 0;
> >   }
> > +static int
> > +process_longform_leaf_root(
> > +	struct xfs_mount	*mp,
> > +	xfs_ino_t		ino,
> > +	struct xfs_dinode	*dip,
> > +	struct blkmap		*blkmap,
> > +	int			*repair,
> > +	struct xfs_buf		*bp)
> > +{
> > +	struct xfs_attr3_icleaf_hdr leafhdr;
> > +	xfs_dahash_t		next_hashval;
> > +	int			badness;
> "badness" pretty much just looks like "error" here?  Or is it different in
> some way?

The return value for process_leaf_attr_block is 1 if the attr block is
bad and 0 for the attr block is ok.  It's not the usual -EFUBAR error
codes that we use in many other parts of xfs.

> > +	int			repairlinks = 0;
> > +
> > +	/*
> > +	 * check sibling pointers in leaf block or root block 0 before
> > +	 * we have to release the btree block
> > +	 */
> > +	xfs_attr3_leaf_hdr_from_disk(mp->m_attr_geo, &leafhdr, bp->b_addr);
> > +	if (leafhdr.forw != 0 || leafhdr.back != 0)  {
> > +		if (!no_modify)  {
> > +			do_warn(
> > +_("clearing forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"),
> > +				ino);
> > +			repairlinks = 1;
> > +			leafhdr.forw = 0;
> > +			leafhdr.back = 0;
> > +			xfs_attr3_leaf_hdr_to_disk(mp->m_attr_geo, bp->b_addr,
> > +					&leafhdr);
> > +		} else  {
> > +			do_warn(
> > +_("would clear forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"), ino);
> > +		}
> > +	}
> > +
> > +	badness = process_leaf_attr_block(mp, bp->b_addr, 0, ino, blkmap, 0,
> > +			&next_hashval, repair);
> > +	if (badness) {
> > +		*repair = 0;
> > +		/* the block is bad.  lose the attribute fork. */
> > +		libxfs_putbuf(bp);
> > +		return 1;
> > +	}
> > +
> > +	*repair = *repair || repairlinks;
> > +
> > +	if (*repair && !no_modify)
> > +		libxfs_writebuf(bp, 0);
> > +	else
> > +		libxfs_putbuf(bp);
> > +
> > +	return 0;
> > +}
> > +
> > +static int
> > +process_longform_da_root(
> > +	struct xfs_mount	*mp,
> > +	xfs_ino_t		ino,
> > +	struct xfs_dinode	*dip,
> > +	struct blkmap		*blkmap,
> > +	int			*repair,
> > +	struct xfs_buf		*bp)
> > +{
> > +	struct xfs_da3_icnode_hdr	da3_hdr;
> > +	int			repairlinks = 0;
> > +	int			error;
> > +
> > +	libxfs_da3_node_hdr_from_disk(mp, &da3_hdr, bp->b_addr);
> > +	/*
> > +	 * check sibling pointers in leaf block or root block 0 before
> > +	 * we have to release the btree block
> > +	 */
> > +	if (da3_hdr.forw != 0 || da3_hdr.back != 0)  {
> > +		if (!no_modify)  {
> > +			do_warn(
> > +_("clearing forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"),
> > +				ino);
> > +
> > +			repairlinks = 1;
> > +			da3_hdr.forw = 0;
> > +			da3_hdr.back = 0;
> > +			xfs_da3_node_hdr_to_disk(mp, bp->b_addr, &da3_hdr);
> > +		} else  {
> > +			do_warn(
> > +_("would clear forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"), ino);
> > +		}
> > +	}
> > +
> > +	/* must do this now, to release block 0 before the traversal */
> Did you mean to reference *repair here without setting it?  I guess it was
> like that from the code it was taken from, but it makes it looks like repair
> is both an in and an out.  I wonder if it's really needed in the check
> below?

*repair is passed from a stack variable in process_inode_attr_fork ->
process_attributes -> process_longform_attr.  It's initialized properly,
but the code doesn't make it easy to figure that out since that's three
functions up in the call stack and anyone is allowed to mess with it.

One of the grottier bits of xfs_repair is that the return values for
those functions also have meaning...I think return 1 means "zap this
whole thing" vs. *repair ==1 means "we fixed it".

--D

> 
> Allison
> 
> > +	if ((*repair || repairlinks) && !no_modify) {
> > +		*repair = 1;
> > +		libxfs_writebuf(bp, 0);
> > +	} else
> > +		libxfs_putbuf(bp);
> > +	error = process_node_attr(mp, ino, dip, blkmap); /* + repair */
> > +	if (error)
> > +		*repair = 0;
> > +	return error;
> > +}
> > +
> >   /*
> >    * Start processing for a leaf or fuller btree.
> >    * A leaf directory is one where the attribute fork is too big for
> > @@ -963,19 +1063,15 @@ _("wrong FS UUID, inode %" PRIu64 " attr block %" PRIu64 "\n"),
> >    */
> >   static int
> >   process_longform_attr(
> > -	xfs_mount_t	*mp,
> > -	xfs_ino_t	ino,
> > -	xfs_dinode_t	*dip,
> > -	blkmap_t	*blkmap,
> > -	int		*repair)	/* out - 1 if something was fixed */
> > +	struct xfs_mount	*mp,
> > +	xfs_ino_t		ino,
> > +	struct xfs_dinode	*dip,
> > +	struct blkmap		*blkmap,
> > +	int			*repair) /* out - 1 if something was fixed */
> >   {
> > -	xfs_attr_leafblock_t	*leaf;
> > -	xfs_fsblock_t	bno;
> > -	xfs_buf_t	*bp;
> > -	xfs_dahash_t	next_hashval;
> > -	int		repairlinks = 0;
> > -	struct xfs_attr3_icleaf_hdr leafhdr;
> > -	int		error;
> > +	xfs_fsblock_t		bno;
> > +	struct xfs_buf		*bp;
> > +	struct xfs_da_blkinfo	*info;
> >   	*repair = 0;
> > @@ -1015,74 +1111,31 @@ process_longform_attr(
> >   		return 1;
> >   	}
> > -	/* verify leaf block */
> > -	leaf = bp->b_addr;
> > -	xfs_attr3_leaf_hdr_from_disk(mp->m_attr_geo, &leafhdr, leaf);
> > -
> > -	/* check sibling pointers in leaf block or root block 0 before
> > -	* we have to release the btree block
> > -	*/
> > -	if (leafhdr.forw != 0 || leafhdr.back != 0)  {
> > -		if (!no_modify)  {
> > -			do_warn(
> > -	_("clearing forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"),
> > -				ino);
> > -			repairlinks = 1;
> > -			leafhdr.forw = 0;
> > -			leafhdr.back = 0;
> > -			xfs_attr3_leaf_hdr_to_disk(mp->m_attr_geo,
> > -						   leaf, &leafhdr);
> > -		} else  {
> > -			do_warn(
> > -	_("would clear forw/back pointers in block 0 for attributes in inode %" PRIu64 "\n"), ino);
> > -		}
> > -	}
> > -
> >   	/*
> >   	 * use magic number to tell us what type of attribute this is.
> >   	 * it's possible to have a node or leaf attribute in either an
> >   	 * extent format or btree format attribute fork.
> >   	 */
> > -	switch (leafhdr.magic) {
> > +	info = bp->b_addr;
> > +	switch (be16_to_cpu(info->magic)) {
> >   	case XFS_ATTR_LEAF_MAGIC:	/* leaf-form attribute */
> >   	case XFS_ATTR3_LEAF_MAGIC:
> > -		if (process_leaf_attr_block(mp, leaf, 0, ino, blkmap,
> > -				0, &next_hashval, repair)) {
> > -			*repair = 0;
> > -			/* the block is bad.  lose the attribute fork. */
> > -			libxfs_putbuf(bp);
> > -			return(1);
> > -		}
> > -		*repair = *repair || repairlinks;
> > -		break;
> > -
> > +		return process_longform_leaf_root(mp, ino, dip, blkmap, repair,
> > +				bp);
> >   	case XFS_DA_NODE_MAGIC:		/* btree-form attribute */
> >   	case XFS_DA3_NODE_MAGIC:
> > -		/* must do this now, to release block 0 before the traversal */
> > -		if ((*repair || repairlinks) && !no_modify) {
> > -			*repair = 1;
> > -			libxfs_writebuf(bp, 0);
> > -		} else
> > -			libxfs_putbuf(bp);
> > -		error = process_node_attr(mp, ino, dip, blkmap); /* + repair */
> > -		if (error)
> > -			*repair = 0;
> > -		return error;
> > +		return process_longform_da_root(mp, ino, dip, blkmap, repair,
> > +				bp);
> >   	default:
> >   		do_warn(
> >   	_("bad attribute leaf magic # %#x for dir ino %" PRIu64 "\n"),
> > -			be16_to_cpu(leaf->hdr.info.magic), ino);
> > +			be16_to_cpu(info->magic), ino);
> >   		libxfs_putbuf(bp);
> >   		*repair = 0;
> > -		return(1);
> > +		return 1;
> >   	}
> > -	if (*repair && !no_modify)
> > -		libxfs_writebuf(bp, 0);
> > -	else
> > -		libxfs_putbuf(bp);
> > -
> > -	return(0);  /* repair may be set */
> > +	return 0; /* should never get here */
> >   }
> >