This was noticed on Mac OS X where, if the default route is returned,
RTA_NETMASK has sa_len set to 0, but skipping zero bytes to read the
next address makes no sense, of course. Using 0 for sa_len seems
a bit strange, in particular, because struct sockaddr has by definition
a minimum length of 16 bytes. But it seems FreeBSD actually does the
same.
If a transport/BEET SA has different selectors for different proto/ports,
installing just the proto/port of the first SA would break any additional
selector.
Previously we silently replaced an existing policy with a new one if the
reqid changed for the same selectors. This will break an old policy in the
favour of the new one (for example if two clients behind the same NAT use
transport mode).
With this change any new policy gets rejected if the reqid differs. This will
make sure we break no existing policy. For rekeying and acquires we still can
have overlapping policies (as we use the same reqid), but for unrelated
connections this is not true anymore (it wasn't actually before, we just
silently broke the existing policy).
This new flag gives the kernel-interface a hint how it should priorize the
use of newly installed SAs during rekeying.
Consider the following rekey procedure in IKEv2:
Initiator --- Responder
I1 -------CREATE-------> R1
I2 <------CREATE--------
-------DELETE-------> R2
I3 <------DELETE--------
SAs are always handled as pairs, the following happens at the SA level:
* Initiator starts the exchange at I1
* Responder installs new SA pair at R1
* Initiator installs new SA pair at I2
* Responder removes old SA pair at R2
* Initiator removes old SA pair at I3
This makes sure SAs get installed/removed overlapping during rekeying. However,
to avoid any packet loss, it is crucial that the new outbound SA gets
activated at the correct position:
* as exchange initiator, in I2
* as exchange responder, in R2
This should guarantee that we don't use the new outbound SA before the peer
could install its corresponding inbound SA.
The new parameter allows the kernel backend to install the new SA with
appropriate priorities, i.e. it should:
* as exchange inititator, have the new outbound SA installed with higher
priority than the old SA
* as exchange responder, have the new outbound SA installed with lower
priority than the old SA
While we could split up the SA installation at the responder, this approach
has another advantage: it allows the kernel backend to switch SAs based on
other criteria, for example when receiving traffic on the new inbound SA.
If routes installed along with policies covering the peer address affect local
IKE/ESP packets, they won't get routed correctly. To work around this issue,
the kernel interface can install "exclude" routes for the IKE peer. Not all
networking backends require this workaround, hence we export a flag for it
if it is required.
As forwarding policies are not available on all systems (OS X), using the
forward policy to attach the route is a bad pick. Using input policies allows
OS X to install routes.
Tobias Brunner