Merge branch 'ip-ingress-skb-reason'

Menglong Dong says:

====================
net: ip: add skb drop reasons to ip ingress

In the series "net: use kfree_skb_reason() for ip/udp packet receive",
skb drop reasons are added to the basic ingress path of IPv4. And in
the series "net: use kfree_skb_reason() for ip/neighbour", the egress
paths of IPv4 and IPv6 are handled. Related links:

https://lore.kernel.org/netdev/20220205074739.543606-1-imagedong@tencent.com/
https://lore.kernel.org/netdev/20220226041831.2058437-1-imagedong@tencent.com/

Seems we still have a lot work to do with IP layer, including IPv6 basic
ingress path, IPv4/IPv6 forwarding, IPv6 exthdrs, fragment and defrag,
etc.

In this series, skb drop reasons are added to the basic ingress path of
IPv6 protocol and IPv4/IPv6 packet forwarding. Following functions, which
are used for IPv6 packet receiving are handled:

  ip6_pkt_drop()
  ip6_rcv_core()
  ip6_protocol_deliver_rcu()

And following functions that used for IPv6 TLV parse are handled:

  ip6_parse_tlv()
  ipv6_hop_ra()
  ipv6_hop_ioam()
  ipv6_hop_jumbo()
  ipv6_hop_calipso()
  ipv6_dest_hao()

Besides, ip_forward() and ip6_forward(), which are used for IPv4/IPv6
forwarding, are also handled. And following new drop reasons are added:

  /* host unreachable, corresponding to IPSTATS_MIB_INADDRERRORS */
  SKB_DROP_REASON_IP_INADDRERRORS
  /* network unreachable, corresponding to IPSTATS_MIB_INADDRERRORS */
  SKB_DROP_REASON_IP_INNOROUTES
  /* packet size is too big, corresponding to
   * IPSTATS_MIB_INTOOBIGERRORS
   */
  SKB_DROP_REASON_PKT_TOO_BIG

In order to simply the definition and assignment for
'enum skb_drop_reason', some helper functions are introduced in the 1th
patch. I'm not such if this is necessary, but it makes the code simpler.
For example, we can replace the code:

  if (reason == SKB_DROP_REASON_NOT_SPECIFIED)
          reason = SKB_DROP_REASON_IP_INHDR;

with:

  SKB_DR_OR(reason, IP_INHDR);

In the 6th patch, the statistics for skb in ipv6_hop_jum() is removed,
as I think it is redundant. There are two call chains for
ipv6_hop_jumbo(). The first one is:

  ipv6_destopt_rcv() -> ip6_parse_tlv() -> ipv6_hop_jumbo()

On this call chain, the drop statistics will be done in
ipv6_destopt_rcv() with 'IPSTATS_MIB_INHDRERRORS' if ipv6_hop_jumbo()
returns false.

The second call chain is:

  ip6_rcv_core() -> ipv6_parse_hopopts() -> ip6_parse_tlv()

And the drop statistics will also be done in ip6_rcv_core() with
'IPSTATS_MIB_INHDRERRORS' if ipv6_hop_jumbo() returns false.

Therefore, the statistics in ipv6_hop_jumbo() is redundant, which
means the drop is counted twice. The statistics in ipv6_hop_jumbo()
is almost the same as the outside, except the
'IPSTATS_MIB_INTRUNCATEDPKTS', which seems that we have to ignore it.

======================================================================

Here is a basic test for IPv6 forwarding packet drop that monitored by
'dropwatch' tool:

  drop at: ip6_forward+0x81a/0xb70 (0xffffffff86c73f8a)
  origin: software
  input port ifindex: 7
  timestamp: Wed Apr 13 11:51:06 2022 130010176 nsec
  protocol: 0x86dd
  length: 94
  original length: 94
  drop reason: IP_INADDRERRORS

The origin cause of this case is that IPv6 doesn't allow to forward the
packet with LOCAL-LINK saddr, and results the 'IP_INADDRERRORS' drop
reason.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

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