netdev - [PATCH v2 0/4] GSO_BY_FRAGS correctness improvements

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Date:   Thu,  1 Mar 2018 17:13:36 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     netdev@...r.kernel.org
Cc:     Daniel Axtens <dja@...ens.net>
Subject: [PATCH v2 0/4] GSO_BY_FRAGS correctness improvements

As requested [1], I went through and had a look at users of gso_size to
see if there were things that need to be fixed to consider
GSO_BY_FRAGS, and I have tried to improve our helper functions to deal
with this case.

I found a few. This fixes bugs relating to the use of
skb_gso_*_seglen() where GSO_BY_FRAGS is not considered.

Patch 1 renames skb_gso_validate_mtu to skb_gso_validate_network_len.
This is follow-up to my earlier patch 2b16f048729b ("net: create
skb_gso_validate_mac_len()"), and just makes everything a bit clearer.

Patches 2 and 3 replace the final users of skb_gso_network_seglen() -
which doesn't consider GSO_BY_FRAGS - with
skb_gso_validate_network_len(), which does. This allows me to make the
skb_gso_*_seglen functions private in patch 4 - now future users won't
accidentally do the wrong comparison.

Two things remain. One is qdisc_pkt_len_init, which is discussed at
[2] - it's caught up in the GSO_DODGY mess. I don't have any expertise
in GSO_DODGY, and it looks like a good clean fix will involve
unpicking the whole validation mess, so I have left it for now.

Secondly, there are 3 eBPF opcodes that change the gso_size of an SKB
and don't consider GSO_BY_FRAGS. This is going through the bpf tree.

Regards,
Daniel

[1] https://patchwork.ozlabs.org/comment/1852414/
[2] https://www.spinics.net/lists/netdev/msg482397.html

PS: This is all in the core networking stack. For a driver to be
affected by this it would need to support NETIF_F_GSO_SCTP /
NETIF_F_GSO_SOFTWARE and then either use gso_size or not be a purely
virtual device. (Many drivers look at gso_size, but do not support
SCTP segmentation, so the core network will segment an SCTP gso before
it hits them.) Based on that, the only driver that may be affected is
sunvnet, but I have no way of testing it, so I haven't looked at it.

v2: split out bpf stuff
    fix review comments from Dave Miller

Daniel Axtens (4):
  net: rename skb_gso_validate_mtu -> skb_gso_validate_network_len
  net: sched: tbf: handle GSO_BY_FRAGS case in enqueue
  net: xfrm: use skb_gso_validate_network_len() to check gso sizes
  net: make skb_gso_*_seglen functions private

 include/linux/skbuff.h                  | 35 +-----------------------
 net/core/skbuff.c                       | 48 ++++++++++++++++++++++++++++-----
 net/ipv4/ip_forward.c                   |  2 +-
 net/ipv4/ip_output.c                    |  2 +-
 net/ipv4/netfilter/nf_flow_table_ipv4.c |  2 +-
 net/ipv4/xfrm4_output.c                 |  3 ++-
 net/ipv6/ip6_output.c                   |  2 +-
 net/ipv6/netfilter/nf_flow_table_ipv6.c |  2 +-
 net/ipv6/xfrm6_output.c                 |  2 +-
 net/mpls/af_mpls.c                      |  2 +-
 net/sched/sch_tbf.c                     |  3 ++-
 net/xfrm/xfrm_device.c                  |  2 +-
 12 files changed, 54 insertions(+), 51 deletions(-)

-- 
2.14.1