• Hannes Frederic Sowa's avatar
    ipv4: ipv6: better estimate tunnel header cut for correct ufo handling · 91a48a2e
    Hannes Frederic Sowa authored
    Currently the UFO fragmentation process does not correctly handle inner
    UDP frames.
    
    (The following tcpdumps are captured on the parent interface with ufo
    disabled while tunnel has ufo enabled, 2000 bytes payload, mtu 1280,
    both sit device):
    
    IPv6:
    16:39:10.031613 IP (tos 0x0, ttl 64, id 3208, offset 0, flags [DF], proto IPv6 (41), length 1300)
        192.168.122.151 > 1.1.1.1: IP6 (hlim 64, next-header Fragment (44) payload length: 1240) 2001::1 > 2001::8: frag (0x00000001:0|1232) 44883 > distinct: UDP, length 2000
    16:39:10.031709 IP (tos 0x0, ttl 64, id 3209, offset 0, flags [DF], proto IPv6 (41), length 844)
        192.168.122.151 > 1.1.1.1: IP6 (hlim 64, next-header Fragment (44) payload length: 784) 2001::1 > 2001::8: frag (0x00000001:0|776) 58979 > 46366: UDP, length 5471
    
    We can see that fragmentation header offset is not correctly updated.
    (fragmentation id handling is corrected by 916e4cf4 ("ipv6: reuse
    ip6_frag_id from ip6_ufo_append_data")).
    
    IPv4:
    16:39:57.737761 IP (tos 0x0, ttl 64, id 3209, offset 0, flags [DF], proto IPIP (4), length 1296)
        192.168.122.151 > 1.1.1.1: IP (tos 0x0, ttl 64, id 57034, offset 0, flags [none], proto UDP (17), length 1276)
        192.168.99.1.35961 > 192.168.99.2.distinct: UDP, length 2000
    16:39:57.738028 IP (tos 0x0, ttl 64, id 3210, offset 0, flags [DF], proto IPIP (4), length 792)
        192.168.122.151 > 1.1.1.1: IP (tos 0x0, ttl 64, id 57035, offset 0, flags [none], proto UDP (17), length 772)
        192.168.99.1.13531 > 192.168.99.2.20653: UDP, length 51109
    
    In this case fragmentation id is incremented and offset is not updated.
    
    First, I aligned inet_gso_segment and ipv6_gso_segment:
    * align naming of flags
    * ipv6_gso_segment: setting skb->encapsulation is unnecessary, as we
      always ensure that the state of this flag is left untouched when
      returning from upper gso segmenation function
    * ipv6_gso_segment: move skb_reset_inner_headers below updating the
      fragmentation header data, we don't care for updating fragmentation
      header data
    * remove currently unneeded comment indicating skb->encapsulation might
      get changed by upper gso_segment callback (gre and udp-tunnel reset
      encapsulation after segmentation on each fragment)
    
    If we encounter an IPIP or SIT gso skb we now check for the protocol ==
    IPPROTO_UDP and that we at least have already traversed another ip(6)
    protocol header.
    
    The reason why we have to special case GSO_IPIP and GSO_SIT is that
    we reset skb->encapsulation to 0 while skb_mac_gso_segment the inner
    protocol of GSO_UDP_TUNNEL or GSO_GRE packets.
    Reported-by: default avatarWolfgang Walter <linux@stwm.de>
    Cc: Cong Wang <xiyou.wangcong@gmail.com>
    Cc: Tom Herbert <therbert@google.com>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    91a48a2e
ip6_offload.c 8.02 KB