Subject: Re: [PATCH] NET: Proper handling of IPv6 header in tun driver when TUN_NO_PI is set

From: Stephen Hemminger <[email-masked]>
Date: Fri, 6 Jun 2008 13:48:33 -0700

On Fri, 06 Jun 2008 13:21:06 -0700
Max Krasnyanskiy <[email-masked]> wrote:

> Acked-by: Max Krasnyansky <[email-masked]>
> 
> Dave, can you please add this patch to your tree.
> 
> --
> Steve, this is what I meant by "we do not need extra copy_from_user". We 
> already do copy into the SKB and can parse the header right there.
> 
> Max
> 
> 
> 
> 
> Ang Way Chuang wrote:
> > By default, tun.c running in TUN_TUN_DEV mode will set the protocol of 
> > packet to IPv4 if TUN_NO_PI is set. My program failed to work when I 
> > assumed that the driver will check the first nibble of packet, determine 
> > IP version and set the appropriate protocol.
> > 
> > The test for this change was conducted on 2.6.24.7 kernel. But the diff 
> > is produced using git commit
> > c3b25b32e8bef526cca748e1ba023c6bdd705a99. I couldn't test it on kernel 
> > version greater than 2.6.25 due to out of tree driver failing to 
> > compile. But tun_get_user doesn't change that much between 2.6.24 and 
> > 2.6.26, so it should work, I hope :-D. This patch is trivial because 
> > this problem can also be fixed by not using TUN_NO_PI.
> > 
> > Signed-off-by: Ang Way Chuang <[email-masked]>
> > ---
> > 
> > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > index 0ce07a3..77964bc 100644
> > --- a/drivers/net/tun.c
> > +++ b/drivers/net/tun.c
> > @@ -313,6 +313,21 @@ static __inline__ ssize_t tun_get_user(struct 
> > tun_struct *tun, struct iovec *iv,
> > 
> >         switch (tun->flags & TUN_TYPE_MASK) {
> >         case TUN_TUN_DEV:
> > +               if (tun->flags & TUN_NO_PI) {
> > +                       switch (skb->data[0] & 0xf0) {

Why the magic constants, instead of proper casts and defines.
> > +                       case 0x40:
> > +                               pi.proto = __constant_htons(ETH_P_IP);

Use htons() instead of __constant_htons() it is easier to read,
and the compiler already does the right thing.

> > +                               break;
> > +                       case 0x60:
> > +                               pi.proto = __constant_htons(ETH_P_IPV6);
> > +                               break;
> > +                       default:
> > +                               tun->dev->stats.rx_dropped++;
> > +                               kfree_skb(skb);
> > +                               return -EINVAL;
> > +                       }
> > +               }
> > +
> >                 skb_reset_mac_header(skb);
> >                 skb->protocol = pi.proto;
> >                 skb->dev = tun->dev;
> > 
> > -- 
> > 
> 
> --
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