netdev - Re: [ PATCH v1 2/2] ibmveth: Identify ingress large send packets.

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Message-ID: <20201011113125.3f370b77@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sun, 11 Oct 2020 11:31:25 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     David Wilder <dwilder@...ibm.com>,
        Network Development <netdev@...r.kernel.org>,
        tlfalcon@...ux.ibm.com, cris.forno@....com,
        pradeeps@...ux.vnet.ibm.com, wilder@...ibm.com
Subject: Re: [ PATCH v1 2/2] ibmveth: Identify ingress large send packets.

On Sat, 10 Oct 2020 12:51:30 -0400 Willem de Bruijn wrote:
> > > @@ -1385,7 +1386,17 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
> > >                         skb_put(skb, length);
> > >                         skb->protocol = eth_type_trans(skb, netdev);
> > >
> > > -                       if (length > netdev->mtu + ETH_HLEN) {
> > > +                       /* PHYP without PLSO support places a -1 in the ip
> > > +                        * checksum for large send frames.
> > > +                        */
> > > +                       if (be16_to_cpu(skb->protocol) == ETH_P_IP) {

You can byteswap the constant, so its done at compilation time.

> > > +                               struct iphdr *iph = (struct iphdr *)skb->data;
> > > +
> > > +                               iph_check = iph->check;  
> >
> > Check against truncated/bad packets.  
> 
> .. unless I missed context. Other code in this driver seems to peek in
> the network and transport layer headers without additional geometry
> and integrity checks, too.

Good catch, even if we trust the hypervisor to only forward valid
frames this needs to be at least mentioned in the commit message.

Also please add Fixes tags to both patches.