On Linux, setting the source address is insufficient to force a packet to be
sent over a certain path. The kernel uses the best route to select the outgoing
interface, even if we set a source address of a lower priority interface. This
is not only true for interfaces attaching to the same subnet, but also for
unrelated interfaces; the kernel (at least on 4.7) sends out the packet on
whatever interface it sees fit, even if that network does not expect packets
from the source address we force to.
When a better interface becomes available, strongSwan sends its MOBIKE address
list update using the old source address. But the kernel sends that packet over
the new best interface. If that network drops packets having the unexpected
source address from the old path, the MOBIKE update fails and the SA finally
times out.
To enforce a specific interface for our packet, we explicitly set the interface
index from the interface where the source address is installed. According to
ip(7), this overrules the specified source address to the primary interface
address. As this could have side effects to installations using multiple
addresses on a single interface, we disable the option by default for now.
This also allows using IPv6 link-local addresses, which won't work if
the outbound interface is not set explicitly.
If a the original responder narrows the selectors of its peer in addrblock,
the peer gets a subset of that selectors. However, once the original responder
initiates rekeying of that CHILD_SA, it sends the full selectors to the peer,
and then narrows the received selectors locally for the installation, only.
This is insufficient, as the peer ends up with wider selectors, sending traffic
that the original responder will reject to the stricter IPsec policy. So
additionally narrow the selectors when rekeying CHILD_SAs before sending the
TS list to the peer.
Previously, the client had to propose no wider selectors than the certificate
permits, otherwise the complete CHILD_SA was rejected. However, with IKEv2
we can dynamically narrow the selectors to what the certificate allows. This
makes client and gateway configurations very simple by just proposing 0.0.0.0/0,
narrowed to selectors the client is permitted to route into the network.
This allows a gateway to enforce the addrblock policy on certificates that
actually have the extension only. For (legacy) certificates not having the
extension, traffic selectors are validated/narrowed by other means, most
likely by the configuration.
While RFC 3779 says we SHOULD mark it is critical, this has severe side effects
in practice. The addrblock extension is not widely used nor implemented, and
only a few applications can handle this extension. By marking it critical,
none of these applications can make use of such certificates where included
addrblocks do not matter, such as TLS/HTTPS.
If an application wants to make use of addrblocks, that is usually an explicit
decision. Then the very same application obviously can handle addrblocks, and
there is no need for the extension to be critical. In other words, for local
policy checks it is a local matter to handle the extension, hence making it
critical is usually not of much help.
When multihomed, a setup might prefer to dynamically stay on the cheapest
available path by using MOBIKE migrations. If the cheapest path goes away and
comes back, we currently stay on the more expensive path to reduce noise and
prevent potential migration issues. This is usually just fine for links not
generating real cost.
If we have more expensive links in the setup, it can be desirable to always
migrate to the cheapest link available. By setting charon.prefer_best_path,
charon tries to migrate to the path using the highest priority link, allowing
an external application to update routes to indirectly control MOBIKE behavior.
This option has no effect if MOBIKE is unavailable.
For table dumps the kernel accepts RTA_PREFSRC to filter the routes, which is
what we do when doing userspace route calculations. For kernel-based route
lookups, however, the RTA_PREFSRC attribute is ignored and we must specify
RTA_SRC for policy based route lookups.
For gateways with many connections, installing routes is often disabled,
as we can use a static route configuration to achieve proper routing with
a single rule. If this is the case, there is no need to dump all routes and
do userspace route lookups, as there is no need to exclude routes we installed
ourself.
Doing kernel-based route lookups is not only faster with may routes, but also
can use the full power of Linux policy based routing; something we can hardly
rebuild in userspace when calculating routes.
When using vici over RPyC and its (awesome) splitbrain, encoding and decoding
strings fails in vici, most likely because of the Monkey-Patch magic splitbrain
uses.
When specifying the implicit UTF-8 as encoding scheme explicitly, Python uses
the correct method to encode/decode the string, making vici useable in
splitbrain contexts.
Recent research demonstrates that at least for 1024-bit DH groups, it is
possible to create specially crafted primes having a backdoor. From the
prime itself this is not detectable, creating a perfect NOBUS attack.
http://eprint.iacr.org/2016/961
For the primes defined in RFC 5114 no information is provided on how these
have been selected. In the default proposal we included one of the 2048-bit
primes only, where it is questionable if constructing a backdoored prime is
feasible. Nevertheless, this patch removes the group from the set of default
proposals as well.
If the af-alg plugin is enabled, but kernel support is missing, we get
an error line during startup for each probed algorithm. This is way too
verbose, so just skip probing if AF_ALG is unsupported.
If two IKE configurations have CHILD configurations with the same name,
we have no control about the CHILD_SA that actually gets controlled. The
new "ike" parameter specifies the peer config name to find the "child" config
under.
In some situations the vici client is not interested in waiting for a
timeout at all, so don't register a logging callback if the timeout argument
is negative.
With LinuxThreads, poll() is unfortunately no cancellation point. It seems
that poll gets woken up after cancellation, but we actively must check
for cancellation before re-entering poll to properly shut down the watcher
thread.
Previously the constraints in the authentication configuration of an
initiator were enforced only after all authentication rounds were
complete. This posed a problem if an initiator used EAP or PSK
authentication while the responder was authenticated with a certificate
and if a rogue server was able to authenticate itself with a valid
certificate issued by any CA the initiator trusted.
Because any constraints for the responder's identity (rightid) or other
aspects of the authentication (e.g. rightca) the initiator had were not
enforced until the initiator itself finished its authentication such a rogue
responder was able to acquire usernames and password hashes from the client.
And if a client supported EAP-GTC it was even possible to trick it into
sending plaintext passwords.
This patch enforces the configured constraints right after the responder's
authentication successfully finished for each round and before the initiator
starts with its own authentication.
Fixes CVE-2015-4171.
Martin Willi