Messages in this thread | | | Subject | Re: [PATCH v3] vfs: new O_NODE open flag | From | Miklos Szeredi <> | Date | Mon, 07 Dec 2009 07:08:34 +0100 |
| |
On Sat, 5 Dec 2009, Alan Cox wrote: > On Sat, 05 Dec 2009 21:35:55 +0100 > Miklos Szeredi <miklos@szeredi.hu> wrote: > > > On Sat, 5 Dec 2009, Alan Cox wrote: > > > I am concerned primarily about the lack of ability to get rid of such a > > > handle in a controlled fashion. The udev/device unload case is simply one > > > obvious way to exploit it. > > > > I don't understand your concern. Can you please ellaborate on the way > > to exploit O_NODE? > > You end up with a handle to an object which then changes meaning if a > device is unloaded and something else loaded (or consider a pty > recreation)
OK.
> In the normal udev course of things this is ok because even without > revoke udev can just about get away with it for the sole reason it knows > that the handle cannot be open in any form during the driver unload > (because of the device refcounting). You seem to break that.
No. Udev is ok, because it already does revoke access to the device on unloading:
:/* Reset permissions on the device node, before unlinking it to make sure, : * that permissions of possible hard links will be removed too. : */ :int util_unlink_secure(struct udev *udev, const char *filename) :{ : int err; : : chmod(filename, 0000); ...
So I think we agree, that some sort of revoke is needed. But just resetting the permissions is fine, there's no need to actually revoke access for the file descriptor opened with O_NODE.
Do you agree?
Thanks, Miklos
| |