ACK/Cmnt: [SRU X/B/D] CVE-2020-1749 - tunnels over IPv6 are unencrypted when using IPsec

[Stefan Bader]

On 06.05.20 04:23, Thadeu Lima de Souza Cascardo wrote:
> BugLink: https://bugs.launchpad.net/bugs/1876982
> 
> I decided to open a bug, though this is a CVE, in order to document the testing
> that I did on all 3 series.
> 
> [Impact]
> When tunnels are configured over IPv6 using a xfrm policy, it's ignored. That
> means data will be unencrypted when it shouldn't.
> 
> [Test case]
> 
> Launch a VM with the given kernel and monitor its network link on the host with:
> tcpdump -n -i virbr0 ip6 and port 4789
> 
> In the guest, set up a tunnel using an IPv6 address:
> ip link add type vxlan id 5 remote fd00:cafe::2 dstport 4789
> 
> When setting the link up, observe packets being output on the host side:
> ip link set vxlan0 up
> 
> Set the link down, and add a xfrm policy to block output to that given IPv6
> address:
> ip link set vxlan0 down
> ip xfrm policy add dst fd00:cafe::2 dir out action block
> 
> Check that using ping won't work with Operation not permitted:
> ping6 fd00:cafe::2
> connect: Operation not permitted
> 
> Set the vxlan link up and watch that no packets appear on tcpdump:
> ip link set vxlan0 up
> 
> [Regression potential]
> Tunnels like VXLAN, GENEVE, etc, will stop to send. The test has shown that it
> still sends at least when no xfrm policy is configured. Other potential
> regressions are possible, testing those tunnel paths and failure paths would be
> desirable, but hard to do.
> 
> 
> 
The regression potential comment makes me a bit nervous. I guess the other
tunnel types probably would not have worked before with xfrm_policy set. But
that does not prevent people from declaring it a regression.
Maybe this would be a case where we try first with Xenial (which requires the
lesser number of re-do's if things go wrong and probably still has a wider
audience).

Acked-by: Stefan Bader <stefan.bader at canonical.com>

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