linux-kernel - Re: [PATCH 2/4] Fix mainline filesystems to handle ATTR_KILL

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Message-Id: <20070821073551.dac4a5dd.jlayton@redhat.com>
Date:	Tue, 21 Aug 2007 07:35:51 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	Timothy Shimmin <tes@....com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	xfs-oss <xfs@....sgi.com>
Subject: Re: [PATCH 2/4] Fix mainline filesystems to handle ATTR_KILL_ bits
 correctly

On Tue, 21 Aug 2007 15:35:08 +1000
Timothy Shimmin <tes@....com> wrote:

> Jeff Layton wrote:
> > This should fix all of the filesystems in the mainline kernels to handle
> > ATTR_KILL_SUID and ATTR_KILL_SGID correctly. For most of them, this is
> > just a matter of making sure that they call generic_attrkill early in
> > the setattr inode op.
> > 
> > Signed-off-by: Jeff Layton <jlayton@...hat.com>
> > ---
> >  fs/xfs/linux-2.6/xfs_iops.c               |    5 ++++-
> > --- a/fs/xfs/linux-2.6/xfs_iops.c
> > +++ b/fs/xfs/linux-2.6/xfs_iops.c
> > @@ -651,12 +651,15 @@ xfs_vn_setattr(
> >  	struct iattr	*attr)
> >  {
> >  	struct inode	*inode = dentry->d_inode;
> > -	unsigned int	ia_valid = attr->ia_valid;
> > +	unsigned int	ia_valid;
> >  	bhv_vnode_t	*vp = vn_from_inode(inode);
> >  	bhv_vattr_t	vattr = { 0 };
> >  	int		flags = 0;
> >  	int		error;
> >  
> > +	generic_attrkill(inode->i_mode, attr);
> > +	ia_valid = attr->ia_valid;
> > +
> >  	if (ia_valid & ATTR_UID) {
> >  		vattr.va_mask |= XFS_AT_UID;
> >  		vattr.va_uid = attr->ia_uid;
> 
> Looks reasonable to me for XFS.
> Acked-by: Tim Shimmin <tes@....com>
> 
> So before, this clearing would happen directly in notify_change()
> and now this won't happen until notify_change() calls i_op->setattr
> which for a particular fs it can call generic_attrkill() to do it.
> So I guess for the cases where i_op->setattr is called outside of
> via notify_change, we don't normally have ATTR_KILL_SUID/SGID
> set so that nothing will happen there?

Right. If neither ATTR_KILL bit is set then generic_attrkill is a
noop.

> I guess just wondering the effect with having the code on all
> setattr's. (I'm not familiar with the code path)
> 

These bits are referenced in very few places in the current kernel
tree -- mostly in the VFS layer. The *only* place I see that they
actually get interpreted into a mode change is in notify_change. So
places that call setattr ops w/o going through notify_change are
not likely to have those bits set.

But hypothetically, if a fs did set ATTR_KILL_* and call setattr
directly, then the setattr would now include a mode change that
clears setuid or setgid bits where it may not have before.

-- 
Jeff Layton <jlayton@...hat.com>
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