linux-kernel - Re: [Xen-devel] [PATCH] xen-pciback: fix up cleanup path when alloc fails

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Date:	Mon, 14 Dec 2015 16:08:13 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Doug Goldstein <cardoe@...doe.com>,
	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Jonathan Creekmore <jonathan.creekmore@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Paul Durrant <paul.durrant@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen-pciback: fix up cleanup path when alloc
 fails

On 02/12/15 14:56, Doug Goldstein wrote:
> On 12/2/15 4:35 AM, David Vrabel wrote:
>> On 26/11/15 20:32, Doug Goldstein wrote:
>>> When allocating a pciback device fails, avoid the possibility of a
>>> use after free.
>>
>> We should not require clearing drvdata for correctness.  We should
>> ensure we retain drvdata for as long as it is needed.
>>
>> I note that pcistub_device_release() has:
>>
>> 	kfree(dev_data);
>> 	pci_set_drvdata(dev, NULL);
>>
>> 	/* Clean-up the device */
>> 	xen_pcibk_config_free_dyn_fields(dev);
>> 	xen_pcibk_config_free_dev(dev);
>>
>> Which should (at a minimum) be reordered to move the kfree(dev_data) to
>> after the calls that require it
>>
>> David
>>
> 
> I apologize but at this point I'm confused at what action I should be
> taking. Are you saying NACK to the original patch and suggesting this as
> the replacement? Or saying that this should be done in addition to the
> original patch?

I'm suggesting that the goal should be to remove all
pci_set_drvdata(dev, NULL) calls and have pciback work correctly without
them.

Konrad's the pciback maintainer though so I'll defer to him on this.

David
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