Re: [PATCH] net: ip_finish_output_gso: If skb_gso_network_seglen exceeds MTU, allow segmentation for gre tunneled skbs

From: wenxu@ucloud.cn
Date: Tue,  9 Aug 2016 15:04:21 +0800

From: wenxu <redacted>

commit b8247f095edd ("net: ip_finish_output_gso: If skb_gso_network_seglen
exceeds MTU, allow segmentation for local udp tunneled skbs")

Given:
     - tap0 and ovs-gre
     - ovs-gre stacked on eth0, eth0 having the small mtu

After encapsulation these skbs have skb_gso_network_seglen that exceed
eth0's ip_skb_dst_mtu. So the finnal each segment would be larger than
eth0 mtu. These packets maybe dropped.

It has the same problem if tap0 bridge with ipgre or gretap device. So
the IPSKB_FRAG_SEGS flags should also be set in gre tunneled skbs.

Signed-off-by: wenxu <redacted>

I am rather certain that this test is intentionally restricted to
UDP tunnel endpoints, because GRE and other tunnel types are PMTU safe.

Hannes and Shmulik?