linux-kernel - Re: [PATCH 6/6] Fix unsafe fw_event

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Date:	Fri, 3 Jul 2015 09:02:51 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Calvin Owens <calvinowens@...com>
Cc:	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 6/6] Fix unsafe fw_event_list usage

On Mon, Jun 08, 2015 at 08:50:56PM -0700, Calvin Owens wrote:
> Since the fw_event deletes itself from the list, cleanup_queue() can
> walk onto garbage pointers or walk off into freed memory.
> 
> This refactors the code in _scsih_fw_event_cleanup_queue() to not
> iterate over the fw_event_list without a lock. 

I think this really should be folded into the previous one, with the
fixes in this one the other refcounting change don't make a whole lot
sense.

> +static struct fw_event_work *dequeue_next_fw_event(struct MPT2SAS_ADAPTER *ioc)
> +{
> +	unsigned long flags;
> +	struct fw_event_work *fw_event = NULL;
> +
> +	spin_lock_irqsave(&ioc->fw_event_lock, flags);
> +	if (!list_empty(&ioc->fw_event_list)) {
> +		fw_event = list_first_entry(&ioc->fw_event_list,
> +				struct fw_event_work, list);
> +		list_del_init(&fw_event->list);
> +		fw_event_work_get(fw_event);
> +	}
> +	spin_unlock_irqrestore(&ioc->fw_event_lock, flags);
> +
> +	return fw_event;

Shouldn't we have a reference for each item on the list that gets
transfer to whomever removes it from the list?

Additionally _firmware_event_work should call dequeue_next_fw_event
first in the function so that item is off the list before we process
it, and can then just drop the reference once it's done.

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