netdev - [RFC ipsec 0/1] xfrm: set-mark default behavior changes

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Message-Id: <20190105003055.116457-1-benedictwong@google.com>
Date:   Fri,  4 Jan 2019 16:30:54 -0800
From:   Benedict Wong <benedictwong@...gle.com>
To:     netdev@...r.kernel.org
Cc:     nharold@...gle.com, benedictwong@...gle.com, lorenzo@...gle.com,
        maze@...gle.com
Subject: [RFC ipsec 0/1] xfrm: set-mark default behavior changes

A behavior change introduced in 9b42c1f179a6 (“xfrm: Extend the
output_mark to support input direction and masking”) results in a
change in:

1. Default outbound behavior with regards to route lookup marks, and
2. Inbound behavior for SAs used to decapsulate packets when the output
     mark (as specified in 4.14 to 4.18) is set.

This patch set restores the previous default outbound behavior,
resolving (1), but behavior change (2) will require more discussion.

Specifically, in (2), a SA with a "output mark" set will now have that
Mark imposed on the inbound packet (As opposed to the previous
output-mark behavior where the inbound packet's mark would not be
touched). This is less of a concern, as it is limited to the case where:

1. SA output mark is set
2. SA is using non-transport mode
3. SA is configured for inbound decapsulation (local dst IP)

Critically, conditions 1 and 3 imply a configuration that output mark
was not designed to support. The only valid use case for this seems
to be the loopback case (as IP addresses would apply bidirectionally).
As such, we believe that this behavioral change is acceptable as is.

Benedict Wong (1):
  xfrm: Make set-mark default behavior backward compatible

 net/xfrm/xfrm_policy.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
2.20.1.97.g81188d93c3-goog