Re: [PATCH V5 04/12] xfs: Check for extent overflow when adding/removing xattrs

From: Chandan Babu R <chandanrlinux@gmail.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org, david@fromorbit.com
Subject: Re: [PATCH V5 04/12] xfs: Check for extent overflow when adding/removing xattrs
Date: Tue, 06 Oct 2020 14:51:15 +0530	[thread overview]
Message-ID: <3262882.2ycmhBttRE@garuda> (raw)
In-Reply-To: <20201006042329.GN49547@magnolia>

On Tuesday 6 October 2020 9:53:29 AM IST Darrick J. Wong wrote:
> On Sat, Oct 03, 2020 at 11:26:25AM +0530, Chandan Babu R wrote:
> > Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to be
> > added. One extra extent for dabtree in case a local attr is large enough
> > to cause a double split.  It can also cause extent count to increase
> > proportional to the size of a remote xattr's value.
> > 
> > Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> 
> Didn't I already review this?  AFAICT it hasn't changed much, but did
> something change enough to warrant dropping the old RVB tag?

Yes, you had reviewed it earlier. Sorry, I missed out on adding the RVB before
sending the patch.

> 
> > ---
> >  fs/xfs/libxfs/xfs_attr.c       | 13 +++++++++++++
> >  fs/xfs/libxfs/xfs_inode_fork.h | 10 ++++++++++
> >  2 files changed, 23 insertions(+)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > index fd8e6418a0d3..be51e7068dcd 100644
> > --- a/fs/xfs/libxfs/xfs_attr.c
> > +++ b/fs/xfs/libxfs/xfs_attr.c
> > @@ -396,6 +396,7 @@ xfs_attr_set(
> >  	struct xfs_trans_res	tres;
> >  	bool			rsvd = (args->attr_filter & XFS_ATTR_ROOT);
> >  	int			error, local;
> > +	int			rmt_blks = 0;
> >  	unsigned int		total;
> >  
> >  	if (XFS_FORCED_SHUTDOWN(dp->i_mount))
> > @@ -442,11 +443,15 @@ xfs_attr_set(
> >  		tres.tr_logcount = XFS_ATTRSET_LOG_COUNT;
> >  		tres.tr_logflags = XFS_TRANS_PERM_LOG_RES;
> >  		total = args->total;
> > +
> > +		if (!local)
> > +			rmt_blks = xfs_attr3_rmt_blocks(mp, args->valuelen);
> >  	} else {
> >  		XFS_STATS_INC(mp, xs_attr_remove);
> >  
> >  		tres = M_RES(mp)->tr_attrrm;
> >  		total = XFS_ATTRRM_SPACE_RES(mp);
> > +		rmt_blks = xfs_attr3_rmt_blocks(mp, XFS_XATTR_SIZE_MAX);
> >  	}
> >  
> >  	/*
> > @@ -460,6 +465,14 @@ xfs_attr_set(
> >  
> >  	xfs_ilock(dp, XFS_ILOCK_EXCL);
> >  	xfs_trans_ijoin(args->trans, dp, 0);
> > +
> > +	if (args->value || xfs_inode_hasattr(dp)) {
> > +		error = xfs_iext_count_may_overflow(dp, XFS_ATTR_FORK,
> > +				XFS_IEXT_ATTR_MANIP_CNT(rmt_blks));
> > +		if (error)
> > +			goto out_trans_cancel;
> 
> Hmm.  If you hit this while trying to remove an xattr, what then?
> I suppose you really don't want to overflow naextents, but I suppose the
> only other option is to delete the file.  Oh well, attr forks with 65533
> extents should be vanishingly rare, right?  Right? :)

Yes, Deleting the corresponding file would be the only option. If we did allow
this operation to succeed we would end up having a silent corruption of the
attr extent counter.

> 
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> --D
> 
> > +	}
> > +
> >  	if (args->value) {
> >  		unsigned int	quota_flags = XFS_QMOPT_RES_REGBLKS;
> >  
> > diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> > index bcac769a7df6..5de2f07d0dd5 100644
> > --- a/fs/xfs/libxfs/xfs_inode_fork.h
> > +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> > @@ -47,6 +47,16 @@ struct xfs_ifork {
> >   */
> >  #define XFS_IEXT_PUNCH_HOLE_CNT		(1)
> >  
> > +/*
> > + * Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to
> > + * be added. One extra extent for dabtree in case a local attr is
> > + * large enough to cause a double split.  It can also cause extent
> > + * count to increase proportional to the size of a remote xattr's
> > + * value.
> > + */
> > +#define XFS_IEXT_ATTR_MANIP_CNT(rmt_blks) \
> > +	(XFS_DA_NODE_MAXDEPTH + max(1, rmt_blks))
> > +
> >  /*
> >   * Fork handling.
> >   */
> 

-- 
chandan