Commit 4094871db1d6 ("udp: only do GSO if # of segs > 1") avoided GSO
for small packets. But the kernel currently dismisses GSO requests only
after checking MTU/PMTU on gso_size. This means any packets, regardless
of their payload sizes, could be dropped when PMTU becomes smaller than
requested gso_size. We encountered this issue in production and it
caused a reliability problem that new QUIC connection cannot be
established before PMTU cache expired, while non GSO sockets still
worked fine at the same time.

Ideally, do not check any GSO related constraints when payload size is
smaller than requested gso_size, and return EMSGSIZE instead of EINVAL
on MTU/PMTU check failure to be more specific on the error cause.

Fixes: 4094871db1d6 ("udp: only do GSO if # of segs > 1")
Signed-off-by: Yan Zhai <yan@cloudflare.com>
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Some lwtunnels have a dst cache for post-transformation dst.
If the packet destination did not change we may end up recording
a reference to the lwtunnel in its own cache, and the lwtunnel
state will never be freed.

Discovered by the ioam6.sh test, kmemleak was recently fixed
to catch per-cpu memory leaks. I'm not sure if rpl and seg6
can actually hit this, but in principle I don't see why not.

Fixes: 8cb3bf8bff3c ("ipv6: ioam: Add support for the ip6ip6 encapsulation")
Fixes: 6c8702c60b88 ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")
Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel")
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250130031519.2716843-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

dst_cache_get() gives us a reference, we need to release it.

Discovered by the ioam6.sh test, kmemleak was recently fixed
to catch per-cpu memory leaks.

Fixes: 985ec6f5e623 ("net: ipv6: rpl_iptunnel: mitigate 2-realloc issue")
Fixes: 40475b63761a ("net: ipv6: seg6_iptunnel: mitigate 2-realloc issue")
Fixes: dce525185bc9 ("net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue")
Reviewed-by: Justin Iurman <justin.iurman@uliege.be>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250130031519.2716843-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Steffen Klassert says:

====================
pull request (net): ipsec 2025-01-27

1) Fix incrementing the upper 32 bit sequence numbers for GSO skbs.
   From Jianbo Liu.

2) Fix an out-of-bounds read on xfrm state lookup.
   From Florian Westphal.

3) Fix secpath handling on packet offload mode.
   From Alexandre Cassen.

4) Fix the usage of skb->sk in the xfrm layer.

5) Don't disable preemption while looking up cache state
   to fix PREEMPT_RT.
   From Sebastian Sewior.

* tag 'ipsec-2025-01-27' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec:
  xfrm: Don't disable preemption while looking up cache state.
  xfrm: Fix the usage of skb->sk
  xfrm: delete intermediate secpath entry in packet offload mode
  xfrm: state: fix out-of-bounds read during lookup
  xfrm: replay: Fix the update of replay_esn->oseq_hi for GSO
====================

Link: https://patch.msgid.link/20250127060757.3946314-1-steffen.klassert@secunet.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Let's register inet6_rtm_deladdr() with RTNL_FLAG_DOIT_PERNET and
hold rtnl_net_lock() before inet6_addr_del().

Now that inet6_addr_del() is always called under per-netns RTNL.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-12-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Let's register inet6_rtm_newaddr() with RTNL_FLAG_DOIT_PERNET
and hold rtnl_net_lock() before __dev_get_by_index().

Now that inet6_addr_add() and inet6_addr_modify() are always
called under per-netns RTNL.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-11-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

inet6_addr_add() and inet6_addr_modify() have the same code to validate
IPv6 lifetime that is done under RTNL.

Let's factorise it out to inet6_rtm_newaddr() so that we can validate
the lifetime without RTNL later.

Note that inet6_addr_add() is called from addrconf_add_ifaddr(), but the
lifetime is INFINITY_LIFE_TIME in the path, so expires and flags are 0.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-10-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

We will convert inet6_rtm_newaddr() to per-netns RTNL.

Except for IFA_F_OPTIMISTIC, cfg.ifa_flags can be set before
__dev_get_by_index().

Let's move ifa_flags setup before __dev_get_by_index() so that
we can set ifa_flags without RTNL.

Also, now it's moved before tb[IFA_CACHEINFO] in preparing for
the next patch.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-9-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

inet6_addr_add() is called from inet6_rtm_newaddr() and
addrconf_add_ifaddr().

inet6_addr_add() looks up dev by __dev_get_by_index(), but
it's already done in inet6_rtm_newaddr().

Let's move the 2nd lookup to addrconf_add_ifaddr() and pass
dev to inet6_addr_add().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-8-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

These functions are called from inet6_ioctl() with a socket's netns
and hold RTNL.

  * SIOCSIFADDR    : addrconf_add_ifaddr()
  * SIOCDIFADDR    : addrconf_del_ifaddr()
  * SIOCSIFDSTADDR : addrconf_set_dstaddr()

Let's use rtnl_net_lock().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-7-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>