To: arjan@infradead.org
CC: matthew@wil.cx, linux-fsdevel@vger.kernel.org,
       linux-kernel@vger.kernel.org
In-reply-to: <1142860423.3114.41.camel@laptopd505.fenrus.org> (message from
	Arjan van de Ven on Mon, 20 Mar 2006 14:13:43 +0100)
Subject: Re: DoS with POSIX file locks?
References: <E1FLIlF-0007zR-00@dorka.pomaz.szeredi.hu>
	 <20060320121107.GE8980@parisc-linux.org>
	 <E1FLJLs-00085u-00@dorka.pomaz.szeredi.hu>
	 <20060320123950.GF8980@parisc-linux.org>
	 <E1FLJsF-0008A7-00@dorka.pomaz.szeredi.hu> <1142860423.3114.41.camel@laptopd505.fenrus.org>
Message-Id: <E1FLKMl-0008Gh-00@dorka.pomaz.szeredi.hu>
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Mon, 20 Mar 2006 14:24:11 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1187
Lines: 27

> > > Right.  Um.  I took it out back in March 2003 after enough people
> > > convinced me it wasn't worth trying to account for all the memory
> > > processes use, and the userbeans project would take care of it anyway.
> > > Haha.
> > > 
> > > It's hard to fix the accounting.  You have to deal with one thread
> > > allocating the lock, and then a different thread freeing it.  We never
> > > actually accounted for posix locks (which are the ones we really needed
> > > to!) and on occasion had current->locks go negative, with all kinds of
> > > associated badness.
> > 
> > Things look fairly straightforward if the accounting is done in
> > files_struct instead of task_struct. 
> 
> that's the wrong place; you can send fd's over unix sockets to other
> processes....

POSIX locks have no association with fd's.  Only the inode and the
"owner" is relevant, where owner is derived from the files_struct
pointer for local locks.

Miklos
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