While 3c12905103 ("ipsec: Add function to compare two ipsec_sa_cfg_t
instances") added a comparison function to avoid issues with non-zeroed
padding, hashes were still calculated using chunk_hash().
The refcount_t for allocating unique marks and interface IDs may overflow or
hit the special value for unique marks/if_ids, in the worst case not setting it
on CHILD_SAs that should have one.
As (potentially two) marks/if_ids are allocated only for newly created CHILD_SAs,
but not for rekeying, this not very likely. Still, if a setup uses
aggressive re-authentication and or re-creates CHILD_SAs every minute,
a gateway with 100'000 tunnels may hit the overflow within a month uptime.
For inbound processing, it can be rather useful to apply the mark to the
packet in the SA, so the associated policy with that mark implicitly matches.
When using %unique as match mark, we don't know the mark beforehand, so
we most likely want to set the mark we match against.
%unique (and the upcoming %same key) are usable in specific contexts only.
To restrict the user from using it in other places where it does not get the
expected results, reject such keywords unless explicitly allowed.
Support for mark=%unique/%unique-dir is implemented by using designated
magic mark values.
Use of masks is orthogonal to the 'unique' feature, as it is useful to be
able to designate portions of the packet mark for other purposes, while
still using different marks for different connections.
When these magic values are masked, their magic meaning is lost.
Perform masking only on explicit mark values.
Closesstrongswan/strongswan#87.
When requiring unique flags for CHILD_SAs, allow the configuration to
request different marks for each direction by using the %unique-dir keyword.
This is useful when different marks are desired for each direction but the
number of peers is not predefined.
An example use case is when implementing a site-to-site route-based VPN
without VTI devices.
A use of 0.0.0.0/0 - 0.0.0.0/0 traffic selectors with identical in/out marks
results in outbound traffic being wrongfully matched against the 'fwd'
policy - for which the underlay 'template' does not match - and dropped.
Using different marks for each direction avoids this issue as the 'fwd' policy
uses the 'in' mark will not match outbound traffic.
Closesstrongswan/strongswan#78.
memeq() is currently used to compare these but if there is padding that
is not initialized the same for two instances the comparison fails.
Using this function ensures the objects are compared correctly.
As we now use the same reqid for multiple CHILD_SAs with the same selectors,
having marks based on the reqid makes not that much sense anymore. Instead we
use unique marks that use a custom identifier. This identifier is reused during
rekeying, keeping the marks constant for any rule relying on it (for example
installed by updown).
This also simplifies handling of reqid allocation, as we do not have to query
the marks that is not yet assigned for an unknown reqid.
This will be useful if the kernel backend has to know how many policies
follow an SA install, for example if it must install all policies concurrently.
Tobias Brunner