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

[wcang@nav6.org]

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) {
+                       case 0x40:
+                               pi.proto = __constant_htons(ETH_P_IP);
+                               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;

--