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Message-ID: <50484345.8040508@redhat.com>
Date: Thu, 06 Sep 2012 08:31:33 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Ric Wheeler <ricwheeler@...il.com>
CC: axboe@...nel.dk, Mike Snitzer <snitzer@...hat.com>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [Ping^3] Re: [PATCH] sg_io: allow UNMAP and WRITE SAME without
CAP_SYS_RAWIO
Il 05/09/2012 22:18, Ric Wheeler ha scritto:
>>
>
> Hi Paolo,
>
> Both of these commands are destructive. WRITE_SAME (if done without the
> discard bits set) can also take a very long time to be destructive and
> tie up the storage.
FORMAT_UNIT has the same characteristics and yet it is allowed (btw, I
don't think WRITE SAME slowness is limited to the case where a real
write is requested; discarding can be just as slow).
Also, the two new commands are anyway restricted to programs that have
write access to the disk. If you have read-only access, you won't be
able to issue any destructive command (there is one exception, START
STOP UNIT is allowed even with read-only capability and is somewhat
destructive).
Honestly, the only reason why these two commands weren't included, is
that the current whitelist is heavily tailored towards CD/DVD burning.
> I think that restricting them to CAP_SYS_RAWIO seems reasonable - better
> to vet and give the appropriate apps the needed capability than to
> widely open up the safety check?
CAP_SYS_RAWIO is so wide in its scope, that anything that requires it is
insecure.
Paolo
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