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

--
Jeff Layton <jlayton@redhat.com>
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