linux-kernel - Re: [PATCH 3/3] block: add back command filter modification via sysfs

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Date:	Wed, 12 Sep 2012 13:41:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <axboe@...nel.dk>,
	Ric Wheeler <rwheeler@...hat.com>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 3/3] block: add back command filter modification via
 sysfs


> +ssize_t blk_filter_store(struct request_queue *q,
> +			 const char *page, size_t count, int rw)
> +{
> +	unsigned long okbits[BLK_SCSI_CMD_PER_LONG], *target_okbits;
> +	bool set;
> +	const char *p = page;
> +	char *endp;
> +	int start = -1, cmd;
> +
> +	if (!q->cmd_filter) {
> +		q->cmd_filter = kmalloc(sizeof(struct blk_cmd_filter),
> +					GFP_KERNEL);
> +		blk_set_cmd_filter_defaults(q->cmd_filter);
> +	}
> +

This also needs CAP_SYS_RAWIO otherwise you have a capability escalation
path.

I'm not really in favour of this patch as is. It's not as flexible as
doing it with a BPF filter which if we are going to have a new API is
going to be cleaner, faster and has a clear understood API plus tools.

With BPF you can do things like enabling command A with option B on a
specific device for a certain block range.


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