Re: /proc filesystem allows bypassing directory permissions on Linux

[Dan Yefimov <dan () lightwave net ru>]

On 24.10.2009 2:39, Pavel Machek wrote:
> > > Original owner did chmod 666... after making sure traditional unix
> > > permissions protect the file. Please look at original mail; it was
> > > subtle but I believe I got it right, and file would not be writable
> > > with /proc unmounted.
> > I remember the original mail content. You're right, you can't reach
> > the file if the procfs is not mounted, but you forget about the
> > race, allowing the guest to create a hardlink to the file in an
> > unrestricted location before the directory access becomes
> > restricted. Again, procfs is just another, specific kind of
> > hardlinks.
>
> Check it again.  There's no race; I check link count before chmod 666.

I didn't see real commands checking the link count, just comments telling about 
it. Not to tell about your script is broken by design. With what object do you 
'chmod 0666 unwritable_file', if that file is not designed for access by anybody 
other than you? This is a rhetorical question.
--

Sincerely Your, Dan.