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    SubjectRe: [PATCH] NET: Proper handling of IPv6 header in tun driver when TUN_NO_PI is set
    On Fri, 06 Jun 2008 13:21:06 -0700
    Max Krasnyanskiy <maxk@qualcomm.com> wrote:

    > Acked-by: Max Krasnyansky <maxk@qualcomm.com>
    >
    > 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 <wcang@nav6.org>
    > > ---
    > >
    > > 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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