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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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