Re: [PATCH net v4 1/4] net: make room for the tunnel header in skb_segment_list()

[Henry Martin]

Tested this on v7.4-rc1 (6628e7d4c6b2, KASAN build) with an
independent reproducer (vxlan, fraglist GRO merged segments with
2-byte headroom, software tunnel GSO):

- unpatched: KASAN slab-use-after-free write of size 2 in
  skb_udp_tunnel_segment+0x1360, then skb_under_panic
  len:-64444 put:-65522, panic;
- with this patch: 149 GSO frames over 150 s, all ~4.8k
  segments correctly forwarded, zero KASAN reports, no panic,
  system stays up.

Tested-by: Henry Martin <bsdhenrymartin@xxxxxxxxx>