netdev - Re: [PATCH net 7/7] rxrpc: Use skb_unshare() rather than skb_cow

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Date:   Sun, 01 Sep 2019 08:11:38 +0100
From:   David Howells <dhowells@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     dhowells@...hat.com, netdev@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 7/7] rxrpc: Use skb_unshare() rather than skb_cow_data()

Hillf Danton <hdanton@...a.com> wrote:

> > +		/* Unshare the packet so that it can be modified for in-place
> > +		 * decryption.
> > +		 */
> > +		if (sp->hdr.securityIndex != 0) {
> > +			struct sk_buff *nskb = skb_unshare(skb, GFP_ATOMIC);
> > +			if (!nskb) {
> > +				rxrpc_eaten_skb(skb, rxrpc_skb_unshared_nomem);
> > +				goto out;
> > +			}
> > +
> > +			if (nskb != skb) {
> > +				rxrpc_eaten_skb(skb, rxrpc_skb_received);
> > +				rxrpc_new_skb(skb, rxrpc_skb_unshared);
> > +				skb = nskb;
> > +				sp = rxrpc_skb(skb);
> > +			}
> > +		}
> 
> Unsharing skb makes it perilous to take a peep at it afterwards.

Ah, good point.  rxrpc_new_skb() should be after the assignment.

David