ip6_tunnel: use the right value for ipv4 min mtu check in ip6_tnl_xmit

[ Upstream commit 82a40777de12728dedf4075453b694f0d1baee80 ]

According to RFC791, 68 bytes is the minimum size of IPv4 datagram every
device must be able to forward without further fragmentation while 576
bytes is the minimum size of IPv4 datagram every device has to be able
to receive, so in ip6_tnl_xmit(), 68(IPV4_MIN_MTU) should be the right
value for the ipv4 min mtu check in ip6_tnl_xmit.

While at it, change to use max() instead of if statement.

Fixes: c9fefa08190f ("ip6_tunnel: get the min mtu properly in ip6_tnl_xmit")
Reported-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index c7b202c1720dbeb205ae5f05cfb2bc6398043e8e..cda63426eefb450e9a49497c7afa916168dfb36d 100644 (file)
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1133,12 +1133,8 @@ route_lookup:
                max_headroom += 8;
                mtu -= 8;
        }
-       if (skb->protocol == htons(ETH_P_IPV6)) {
-               if (mtu < IPV6_MIN_MTU)
-                       mtu = IPV6_MIN_MTU;
-       } else if (mtu < 576) {
-               mtu = 576;
-       }
+       mtu = max(mtu, skb->protocol == htons(ETH_P_IPV6) ?
+                      IPV6_MIN_MTU : IPV4_MIN_MTU);
 
        if (skb_dst(skb) && !t->parms.collect_md)
                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);