On systems that use mark-based routing it may be necessary for
routing lookups to use marks in order for packets to be routed
correctly. An example of such a system is Android, which uses
socket marks to route packets via different networks.
Currently, routing lookups in tunnel mode always use a mark of
zero, making routing incorrect on such systems.
This patch adds a new output_mark element to the xfrm state and
a corresponding XFRMA_OUTPUT_MARK netlink attribute. The output
mark differs from the existing xfrm mark in two ways:
1. The xfrm mark is used to match xfrm policies and states, while
the xfrm output mark is used to set the mark (and influence
the routing) of the packets emitted by those states.
2. The existing mark is constrained to be a subset of the bits of
the originating socket or transformed packet, but the output
mark is arbitrary and depends only on the state.
The use of a separate mark provides additional flexibility. For
example:
- A packet subject to two transforms (e.g., transport mode inside
tunnel mode) can have two different output marks applied to it,
one for the transport mode SA and one for the tunnel mode SA.
- On a system where socket marks determine routing, the packets
emitted by an IPsec tunnel can be routed based on a mark that
is determined by the tunnel, not by the marks of the
unencrypted packets.
- Support for setting the output marks can be introduced without
breaking any existing setups that employ both mark-based
routing and xfrm tunnel mode. Simply changing the code to use
the xfrm mark for routing output packets could xfrm mark could
change behaviour in a way that breaks these setups.
If the output mark is unspecified or set to zero, the mark is not
set or changed.
Tested: make allyesconfig; make -j64
Tested: https://android-review.googlesource.com/452776
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
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