[PATCH net v4 0/3] ipv6: udp6: set dst cache for a connected sk if current not valid

[Alexey Kodanev <alexey.kodanev@oracle.com>]

A new RTF_CACHE route can be created with the socket's dst cache
update between the below calls in udpv6_sendmsg(), when datagram
sending results to ICMPV6_PKT_TOOBIG error:

   dst = ip6_sk_dst_lookup_flow(...)
   ...
release_dst:
    if (dst) {
        if (connected) {
            ip6_dst_store(sk, dst)

Therefore, the new socket's dst cache reset to the old one on
"release_dst:".

The first two patches prepare the code to store dst cache
with ip6_sk_dst_lookup_flow():

  * the first patch adds ip6_dst_store_flow() function with
    commonly used source and destiantion addresses checks using
    the flow information.

  * the second patch adds new argument to ip6_sk_dst_lookup_flow()
    and ability to store dst in the socket's cache. Also, the two
    users of the function are updated without enabling the new
    behavior: pingv6_sendmsg() and udpv6_sendmsg().

The last patch contains the actual fix that removes sk dst cache
update in the end of udpv6_sendmsg(), and allows to do it in
ip6_sk_dst_lookup_flow().

v4: * fix the error in the build of ip_dst_store_flow() reported by
      kbuild test robot due to missing checks for CONFIG_IPV6: add
      new function to ip6_output.c instead of ip6_route.h
    * add 'const' to struct flowi6 in ip6_dst_store_flow()
    * minor commit messages fixes

v3: * instead of moving ip6_dst_store() above udp_v6_send_skb(),
      update socket's dst cache inside ip6_sk_dst_lookup_flow()
      if the current one is invalid
    * the issue not reproduced in 4.1, but starting from 4.2. Add
      one more 'Fixes:' commit that creates new RTF_CACHE route.
      Though, it is also mentioned in the first one


Alexey Kodanev (3):
  ipv6: add a wrapper for ip6_dst_store() with flowi6 checks
  ipv6: allow to cache dst for a connected sk in ip6_sk_dst_lookup_flow()
  ipv6: udp6: set dst cache for a connected sk if current not valid

 include/net/ipv6.h    |  6 ++++--
 net/ipv6/datagram.c   |  9 +--------
 net/ipv6/ip6_output.c | 32 +++++++++++++++++++++++++++++---
 net/ipv6/ping.c       |  2 +-
 net/ipv6/udp.c        | 21 ++-------------------
 5 files changed, 37 insertions(+), 33 deletions(-)

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1.8.3.1