linux-kernel - Re: [PATCH 1/1] Defer skb allocation for both mergeable buffers and big packets in virtio

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Date:	Fri, 20 Nov 2009 08:08:52 -0800
From:	Shirley Ma <mashirle@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, Avi Kivity <avi@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Defer skb allocation for both mergeable buffers
 and big packets in virtio_net

On Fri, 2009-11-20 at 07:19 +0100, Eric Dumazet wrote:
> > +void virtio_free_pages(void *buf)
> > +{
> > +     struct page *page = (struct page *)buf;
> > +
> > +     while (page) {
> > +             __free_pages(page, 0);
> > +             page = (struct page *)page->private;
> > +     }
> > +}
> > +
> 
> Interesting use after free :)

Good catch. This code was run when virtio_net removal. I run many times
of remove virtio_net, and didn't hit any panic :(. Fixed it as below:

void virtio_free_pages(void *buf)
{
	struct page *page = (struct page *)buf;
	struct page *npage;

	while (page) {
		npage = page->private;
		__free_pages(page, 0);
		page = npage;
	}
}

Thanks
Shirley


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