Alexey Kodanev says:

====================
ipv6: udp: set dst cache for a connected sk if current not valid

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 three patches prepare the code to store dst cache
with ip6_sk_dst_lookup_flow():

  * the first patch adds ip6_sk_dst_store_flow() function with
    commonly used source and destiantion addresses checks using
    the flow information.

  * the second patch adds a 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 third patch makes 'connected' variable in udpv6_sendmsg()
    to be consistent with ip6_sk_dst_store_flow(), changes its type
    from int to bool.

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().

v6: * use bool type for a new parameter in ip_sk_dst_lookup_flow()
    * add one more patch to convert 'connected' variable in
      udpv6_sendmsg() from int to bool type. If it shouldn't be
      here I will resend it when the net-next is opened.

v5: * relocate ip6_sk_dst_store_flow() to net/ipv6/route.c and
      rename ip6_dst_store_flow() to ip6_sk_dst_store_flow() as
      suggested by Martin

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

Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>