linux-kernel - Re: [PATCH v3 part1 1/4] sg_io: pass request_queue to blk_verify

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Date:	Fri, 24 May 2013 10:32:23 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	linux-kernel@...r.kernel.org, tj@...nel.org,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Doug Gilbert <dgilbert@...erlog.com>,
	linux-scsi@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v3 part1 1/4] sg_io: pass request_queue to blk_verify_command

Il 24/05/2013 10:03, James Bottomley ha scritto:
>>>>> > >>> Does anyone in the real world actually care about this bug?
>>>> > >>
>>>> > >> Yes, or I would move on and not waste so much time on this.
>>> > > 
>>> > > Fine, so produce a simple fix for this bug which we can discuss that's
>>> > > not tied to this feature.
>> > 
>> > Honestly, I have no idea how this is even possible.
> Really?  It looks to me like a simple block on the commands for disk
> devices in the opcode switch would do it (with a corresponding change to
> sg.c:sg_allow_access).

Which switch?  What I can do is something like this in blk_verify_command:

        if (q->sgio_type == TYPE_ROM)
		return 0;
	if (rq->cmd[0] == 0xA4)
		return -EPERM;
	if (!is_write &&
	    (req->cmd[0] == ... || rq->cmd[0] == ...))
		return -EPERM;

But then the particular patch you're replying to is still necessary,
and you're slowing down blk_verify_command.  It may be fine for stable
and -rc, but IMHO it calls for a better implementation in 3.11.

(Besides, I did it like this because it is what Tejun suggested).

Paolo
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