netdev - Re: [PATCHv2 net-next] netlink: allow large data transfers from user-space

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Date:	Mon, 03 Jun 2013 11:00:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, kaber@...sh.net
Subject: Re: [PATCHv2 net-next] netlink: allow large data transfers from
 user-space

On Mon, 2013-06-03 at 19:41 +0200, Pablo Neira Ayuso wrote:
> Hi Eric!
> 
> On Mon, Jun 03, 2013 at 10:12:39AM -0700, Eric Dumazet wrote:
> > On Mon, 2013-06-03 at 18:39 +0200, Pablo Neira Ayuso wrote:
> > 
> > > +	if (is_vmalloc_addr(skb->head)) {
> > > +		vfree(skb->head);
> > > +		skb->data = NULL;
> > > +	}
> > >  
> > 
> > You probably meant :
> > 
> > 	skb->head = NULL;
> > 
> > Now, cross our fingers we do not skb_orphan() these skb too early :)
> 
> skb_release_all checks for skb->data != NULL to release skb->head as
> it would have been allocated via kmalloc. This didn't look very
> intuitive to me when I hit a panic while testing my patch either.

Oh well, this is probably an old typo because of skb_release_data() name

So we indeed do :

	if (likely(skb->data))
		skb_release_data(skb);

But it really should be

	if (likely(skb->head))
		skb_release_head(skb);

as skb->data is not pointing to the beginning of the area to be freed.

BTW, __alloc_skb_head() inits skb->data to NULL, and leaves skb->head
uninitialized. Thats is really not nice...




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