That method is subject to interface filtering, which isn't ideal for
DHCP traffic that probably uses an internal interface on which the IKE
daemon might be disabled. In that case `giaddr` is set to an incorrect
public IP, which in turn might prevent the plugin from receiving the
DHCP server's unicast response, in particular if the DHCP socket
is bound to the internal interface.
This new approach connects the client socket and thereby determines the
source address to reach the DHCP server.
Closesstrongswan/strongswan#1573
The previous code did not ensure that there was a delay of at least
`try` seconds after each sent request. Instead, whenever the condvar was
signaled, which could be due to retransmitted responses or messages for
unrelated transactions (there could even be spurious wakeups), the counter
was increased and a retransmit sent. So instead of actually waiting for
15 seconds for a response (and sending 4 retransmits over that timespan),
it could happen that all five messages were sent within a second without
enough time to actually receive a response.
Using an absolute timeout that we reuse as long as there was no timeout
and the condvar was signaled for something unrelated, should ensure we
wait at least the intended delay after each sent message.
Closesstrongswan/strongswan#1154
The client identifier serves as unique identifier just like a unique MAC
address would, so even with identity_leases disabled some DHCP servers
might assign unique leases per identity.
This increases the chances that subject DNs that might have been cut
off with the arbitrary previous limit of 64 bytes might now be sent
successfully.
The REQUEST message has the most static overhead in terms of other
options (17 bytes) as compared to DISCOVER (5) and RELEASE (7).
Added to that are 3 bytes for the DHCP message type, which means we have
288 bytes left for the two options based on the client identity (host
name and client identification). Since both contain the same value, a
FQDN identity, which causes a host name option to get added, may be
142 bytes long, other identities like subject DNs may be 255 bytes
long (the maximum for a DHCP option).
According to RFC 2131, the minimum size of the 'options' field is 312
bytes, including the 4 byte magic cookie. There also does not seem to
be any restriction regarding the message length, previously the length
was rounded to a multiple of 64 bytes. The latter might have been
because in BOOTP the options field (or rather vendor-specific area as it
was called back then) had a fixed length of 64 bytes (so max(optlen+4, 64)
might actually have been what was intended), but for DHCP the field is
explicitly variable length, so I don't think it's necessary to pad it.
Since we won't read from the socket reducing the receive buffer saves
some memory and it should also minimize the impact on other processes that
bind the same port (Linux distributes packets to the sockets round-robin).
DHCP servers will respond to port 67 if giaddr is non-zero, which we set
if we are not broadcasting. While such messages are received fine via
RAW socket the kernel will respond with an ICMP port unreachable if no
socket is bound to that port. Instead of opening a dummy socket on port
67 just to avoid the ICMPs we can also just operate with a single
socket, bind it to port 67 and send our requests from that port.
Since SO_REUSEADDR behaves on Linux like SO_REUSEPORT does on other
systems we can bind that port even if a DHCP server is running on the
same host as the daemon (this might have to be adapted to make this work
on other systems, but due to the raw socket the plugin is not that portable
anyway).
The previous code compared the port in the packet to the client port and, if
successful, checked it also against the server port, which, therefore, never
matched, but due to incorrect offsets did skip the BPF_JA. If the client port
didn't match the code also skipped to the instruction after the BPF_JA.
However, the latter was incorrect also and processing would have continued at
the next instruction anyway. Basically, DHCP packets to any port were accepted.
What's not fixed with this is that the kernel returns an ICMP Port
unreachable for packets sent to the server port (67) because we don't
have a socket bound to it.
Fixes: f0212e8837 ("Accept DHCP replies on bootps port, as we act as a relay agent if server address configured")
The value of DHCP_OPTEND is 255. When it is assigned this result in a
sign change as the positive int constant is cast to a signed char and -1
results. Clang 4.0 complains about this.
In certain situations it is desirable to bind the send/receive sockets
for the DHCP address allocation to a particular interface. With this
patch the strongswan.conf option charon.plugins.dhcp.interface can be
used to restrict the DHCP communication to a configurable interface.
Signed-off-by: Thomas Egerer <[email protected]>
This ensures that no threads are active when plugins and the rest of the
daemon are unloaded.
callback_job_t was simplified a lot in the process as its main
functionality is now contained in processor_t. The parent-child
relationships were abandoned as these were only needed to simplify job
cancellation.
Tobias Brunner