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 84ee2eb88121aa3a5add4004aba875adf7f58010..ee8dbd228fe2b82a307f31e769cdb6f03cb55fa7 100644 (file)
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1134,12 +1134,8 @@ 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);
 
        skb_dst_update_pmtu(skb, mtu);
        if (skb->len - t->tun_hlen - eth_hlen > mtu && !skb_is_gso(skb)) {