Re: [PATCH 2/4] Fix mainline filesystems to handle ATTR_KILL_ bits correctly

[Jeff Layton <jlayton@redhat.com>]

On Tue, 21 Aug 2007 17:21:28 -0400
Josef Sipek <jsipek@fsl.cs.sunysb.edu> wrote:

> On Tue, Aug 21, 2007 at 07:35:51AM -0400, Jeff Layton wrote:
> > On Tue, 21 Aug 2007 15:35:08 +1000
> > Timothy Shimmin <tes@sgi.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@redhat.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@sgi.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.
> 

I should probably clarify -- in the hypothetical situation above,
the setattr function would have to call generic_attrkill (as most
filesystems should do with this change).

> It almost sounds like an argument for a new inode op (NULL would use
> generic_attr_kill).
> 

That's not a bad idea at all. I suppose that would be easier than
modifying every fs like this, and it does seem like it might be
cleaner. I need to mull it over, but that might be the best
solution.

-- 
Jeff Layton <jlayton@redhat.com>