linux-kernel - Re: [RFC/PATCH] revoke/frevoke system calls V2

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Date:	Wed, 09 Aug 2006 11:39:59 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Edgar Toernig <froese@....de>
Cc:	Chase Venters <chase.venters@...entec.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, akpm@...l.org,
	viro@...iv.linux.org.uk, tytso@....edu, tigran@...itas.com
Subject: Re: [RFC/PATCH] revoke/frevoke system calls V2

Ar Mer, 2006-08-09 am 10:41 +0200, ysgrifennodd Edgar Toernig:
> If I read the code correctly, the behaviour for hung up ttys is completely
> different: read returns EOF, write returns EIO, select/poll/epoll return
> ready, close works.  As rather boring but totally sane behaviour for an fd.
> 
> But after revoke you get EBADF for any operation, even select or close.

Thats a detail of the proposed implementation that isn't hard to fix.

> And IMHO that's insane that a regular user may close fds in someone else's
> processes (or munmap some of its memory).  I already see people trying
> to exploit bugs in system services:

I can do this already today. In fact the index.html one can be used to
crash certain products now depending on their configuration. Just do

	while { true } do
		cp some.html index.html
		> index.html
	done

with a shell that truncates on > and you'll be able to bus error them if
they mmap and are not well written.

These are not actually changes in behaviour. At any point I can shrink a
file I own and you get read -> 0, mmap access -> bus error. Write
behaviour is new but thats no different to filling the disk up or other
real write errors.


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