On 24.11.2024 00:52, Antonio Quartulli wrote:
On 23/11/2024 23:25, Sergey Ryazanov wrote:
On 21.11.2024 23:17, Antonio Quartulli wrote:
On 20/11/2024 23:56, Sergey Ryazanov wrote:
On 15.11.2024 16:13, Antonio Quartulli wrote:
On 09/11/2024 02:11, Sergey Ryazanov wrote:
On 29.10.2024 12:47, Antonio Quartulli wrote:
An ovpn interface will keep carrier always on and let the user
decide when an interface should be considered disconnected.
This way, even if an ovpn interface is not connected to any peer,
it can still retain all IPs and routes and thus prevent any data
leak.
Signed-off-by: Antonio Quartulli <antonio@xxxxxxxxxxx>
Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
---
drivers/net/ovpn/main.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c
index
eead7677b8239eb3c48bb26ca95492d88512b8d4..eaa83a8662e4ac2c758201008268f9633643c0b6 100644
--- a/drivers/net/ovpn/main.c
+++ b/drivers/net/ovpn/main.c
@@ -31,6 +31,13 @@ static void ovpn_struct_free(struct net_device
*net)
static int ovpn_net_open(struct net_device *dev)
{
+ /* ovpn keeps the carrier always on to avoid losing IP or route
+ * configuration upon disconnection. This way it can prevent
leaks
+ * of traffic outside of the VPN tunnel.
+ * The user may override this behaviour by tearing down the
interface
+ * manually.
+ */
+ netif_carrier_on(dev);
If a user cares about the traffic leaking, then he can create a
blackhole route with huge metric:
# ip route add blackhole default metric 10000
Why the network interface should implicitly provide this
functionality? And on another hand, how a routing daemon can learn
a topology change without indication from the interface?
This was discussed loooong ago with Andrew. Here my last response:
https://lore.kernel.org/all/d896bbd8-2709-4834-a637-
f982fc51fc57@xxxxxxxxxxx/
Thank you for sharing the link to the beginning of the conversation.
Till the moment we have 3 topics regarding the operational state
indication:
1. possible absence of a conception of running state,
2. influence on routing protocol implementations,
3. traffic leaking.
As for conception of the running state, it should exists for
tunneling protocols with a state tracking. In this specific case, we
can assume interface running when it has configured peer with keys.
The protocol even has nice feature for the connection monitoring -
keepalive.
What about a device in MP mode? It doesn't make sense to turn the
carrier off when the MP node has no peers connected.
At the same time I don't like having P2P and MP devices behaving
differently in this regard.
MP with a single network interface is an endless headache. Indeed. On
the other hand, penalizing P2P users just because protocol support MP
doesn't look like a solution either.
On the upper side, with "iroutes" implemented using the system routing
table, routing protocols will be able to detect new routes only when the
related client has connected. (The same for the disconnection)
But this is a bit orthogonal compared to the oper state.
The patch has nothing common with the routes configuration. The main
concern is forcing of the running state indication. And more
specifically, the concern is the given justification for this activity.
Therefore keeping the carrier on seemed the most logical way forward
(at least for now - we can still come back to this once we have
something smarter to implement).
It was shown above how to distinguish between running and non-running
cases.
If an author doesn't want to implement operational state indication
now, then I'm Ok with it. Not a big deal now. I just don't like the
idea to promote the abuse of the running state indicator. Please see
below.
Routing protocols on one hand could benefit from the operational
state indication. On another hand, hello/hold timer values mentioned
in the documentation are comparable with default routing protocols
timers. So, actual improvement is debatable.
Regarding the traffic leading, as I mentioned before, the blackhole
route or a firewall rule works better then implicit blackholing with
a non-running interface.
Long story short, I agree that we might not need a real operational
state indication now. Still protecting from a traffic leaking is not
good enough justification.
Well, it's the so called "persistent interface" concept in VPNs:
leave everything as is, even if the connection is lost.
It's called routing framework abuse. The IP router will choose the
route and the egress interface not because this route is a good option
to deliver a packet, but because someone trick it.
This is what the user wants.
Will be happy to see a study on user's preferences.
OpenVPN (userspace) will tear down the P2P interface upon disconnection,
assuming the --persist-tun option was not specified by the user.
So the interface is gone in any case.
By keeping the netcarrier on we are just ensuring that, if the user
wanted persist-tun, the iface is not actually making decisions on its own.
Regarding a decision on its own. Ethernet interface going to the
not-running state upon lost of carrier from a switch. It's hardly could
be considered a decision of the interface. It's an indication of the fact.
Similarly, beeping of UPS is not its decision to make user's life
miserable, it's the indication of the power line failure. I hope, at
least we are both agree on that a UPS should indicate the line failure.
Back to the 'persist-tun' option. I checked the openvpn(8) man page. It
gives a reasonable hints to use this option to avoid negative outcomes
on internal openvpn process restart. E.g. in case of privilege dropping.
It servers the same purpose as 'persist-key'. And there is no word
regarding traffic leaking.
If somebody have decided that this option gives the funny side-effect
and allows to cut the corners, then I cannot say anything but sorry.
With a tun interface this can be done, now you want to basically drop
this feature that existed for long time and break existing setups.
Amicus Plato, sed magis amica veritas
Yes, I don't want to see this interface misbehaviour advertised as a
security feature. I hope the previous email gives a detailed explanation
why.
If it's going to break existing setup, then end-users can be supported
with a changelog notice explaining how to properly address the risk of
the traffic leaking.
At some circumstance, e.g. Android app, it could be the only way to
prevent traffic leaking. But these special circumstances do not make
solution generic and eligible for inclusion into the mainline code.
Why not? We are not changing the general rule, but just defining a
specific behaviour for a specific driver.
Yeah. This patch is not changing the general rule. The patch breaks it
and the comment in the code makes proud of it. Looks like an old joke
that documented bug become a feature.
From a system administrator or a firmware developer perspective, the
proposed behaviour will look like inconsistency comparing to other
interface types. And this inconsistency requires to be addressed with
special configuration or a dedicated script in a worst case. And I
cannot see justified reason to make their life harder.
For example, I don't think a tun interface goes down when there is no
socket attached to it, still packets are just going to be blackhole'd in
that case. No?
Nope. Tun interface indeed will go into the non-running state on the
detach event. Moreover, the tun module supports running/non-running
indication change upon a command from userspace. But not every userspace
application feel a desire to implement it.
I know it can be implemented in many other different ways..but I
don't see a real problem with keeping this way.
At least routing protocols and network monitoring software will not be
happy to see a dead interface pretending that it's still running.
They won't know that the interface is disconnected, they will possibly
just see traffic being dropped.
Packet loss detection is quite complex operation. So yes, they are
indeed monitoring the interface operational state to warn operator as
soon as possible and take some automatic actions if we are talking about
routing protocols. Some sophisticated monitoring systems even capable to
generate events like 'link unstable' with higher severity if they see
interface operational state flapping in a short period of time.
So yeah, for these kinds of systems, proper operational state indication
is essential.
Generally speaking, saying that interface is running, when module
knows for sure that a packet can not be delivered is a user misguiding.
Or a feature, wanted by the user.
A blackhole/firewall can still be added if the user prefers (and not
use the persistent interface).
The solution with false-indication is not so reliable as it might
look. Interface shutdown, inability of a user-space application to
start, user-space application crash, user-space application restart,
each of them will void the trick. Ergo, blackhole/firewall must be
employed by a security concerned user. What makes the proposed feature
odd.
Yeah, this is what other VPN clients call "kill switch".
Persist-tun is just one piece of the puzzle, yet important.
To summaries, I'm Ok if this change will be merged with a comment like
"For future study" or "To be done" or "To be implemented". But a
comment like "to prevent traffic leaking" or any other comment
implying a "breakthrough security feature" will have a big NACK from
my side.
What if the comment redirects the user to --persist-tun option in order
to clarify the context and the wanted behaviour?
Would that help?
Nope. As it was mentioned above, the are no indication that
'persist-tun' is a 'security' feature even in the current openvpn
documentation.
If the openvpn developers want to keep implementation bug-to-bug
compatible, then feel free to configure the blackhole route on behalf of
end-user by means of the userspace daemon. Nobody will mind.
--
Sergey
