linux-kernel - Re: [RFC v6 03/40] vfs: Add MAY_DELETE_SELF and MAY_DELETE

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Message-ID: <CALCETrWwftQ4jbrLqtnuaSA0z15c4V0qyXHL4X0q5vBochDgqg@mail.gmail.com>
Date:	Fri, 28 Aug 2015 18:04:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Cc:	linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
	LSM List <linux-security-module@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v6 03/40] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD
 permission flags

On Aug 28, 2015 2:54 PM, "Andreas Grünbacher"
<andreas.gruenbacher@...il.com> wrote:
>
> 2015-08-28 23:36 GMT+02:00 Andy Lutomirski <luto@...capital.net>:
> > Silly question from the peanut gallery: is there any such thing as
> > opening an fd pointing at a file such that the "open file description"
> > (i.e. the struct file) captures the right to delete the file?
> >
> > IOW do we need FMODE_DELETE_SELF?
>
> When would that permission be checked, what syscall would you use to
> unlink an open file descriptor?

Good point.  It's remotely plausible that there's some trick with bind
mounts, it's likely possible to unlink a directory by fd (using
unlinkat), and you can *link* a file (with linkat or /proc), but
unlinkat doesn't appear to allow you to unlink a file by fd.

--Andy

>
> Thanks,
> Andreas
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