linux-kernel - Re: [PATCH] block: avoid false positive warnings on ioctl to partition

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Date:	Mon, 13 Feb 2012 17:25:27 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] block: avoid false positive warnings on ioctl to
 partition

> Therefore, this patch silently blocks all ioctls except SG_IO, since
> all of them turned out to be false positives; in case some escaped, it
> should be easily diagnosable or at least bisectable.  The warning text
> is separated for root and non-root, and the deprecation period for root
> users is set to end a year from now.

NAK.

Firstly blocking CAP_SYS_RAWIO access by any means to a partition is
itself nonsense as the process has enough privilege to go poke the
controller I/O registers by hand. That's a gratuitious API breakage.

Secondly SG_IO allows users to read and write blocks outside their partition as
far as I can see from the verify logic. You either need to block it or
smarten up the filter.

What were the SG_IO command blocks that were caught ? It's going to be
pretty trivial to add a filter->partition_ok to some of them if need be.

Anyway it fails both by stopping valid stuff and not stopping insecure and
unsafe stuff.

Alan
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