On 4/26/24 6:24 AM, Daniel P. Berrangé wrote:
On Thu, Apr 25, 2024 at 06:22:33PM +0100, Daniel P. Berrangé wrote:
On Thu, Apr 25, 2024 at 01:38:06AM -0400, Laine Stump wrote:
V2: https://lists.libvirt.org/archives/list/devel@xxxxxxxxxxxxxxxxx/thread/5RTZ6PC3N3CO6X353QUHLVOL43SWQ4JD/
This patch series enables libvirt to use nftables rules rather than
iptables *when setting up virtual networks* (it does *not* add
nftables support to the nwfilter driver).
I deployed on my machine and restarted virtnetworkd, with nft backend
active. I have 2 networks running, and got the following result
table ip libvirt {
chain INPUT {
type filter hook input priority filter; policy accept;
counter packets 363 bytes 30801 jump LIBVIRT_INP
}
chain FORWARD {
type filter hook forward priority filter; policy accept;
counter packets 1 bytes 76 jump LIBVIRT_FWX
counter packets 1 bytes 76 jump LIBVIRT_FWI
counter packets 1 bytes 76 jump LIBVIRT_FWO
}
chain OUTPUT {
type filter hook output priority filter; policy accept;
counter packets 286 bytes 107221 jump LIBVIRT_OUT
}
chain LIBVIRT_INP {
iifname "virbr0" udp dport 53 counter packets 0 bytes 0 accept
iifname "virbr0" tcp dport 53 counter packets 0 bytes 0 accept
iifname "virbr0" udp dport 67 counter packets 1 bytes 320 accept
iifname "virbr0" tcp dport 67 counter packets 0 bytes 0 accept
iifname "virbr1" udp dport 53 counter packets 0 bytes 0 accept
iifname "virbr1" tcp dport 53 counter packets 0 bytes 0 accept
iifname "virbr1" udp dport 67 counter packets 0 bytes 0 accept
iifname "virbr1" tcp dport 67 counter packets 0 bytes 0 accept
}
chain LIBVIRT_OUT {
oifname "virbr0" udp dport 53 counter packets 0 bytes 0 accept
oifname "virbr0" tcp dport 53 counter packets 0 bytes 0 accept
oifname "virbr0" udp dport 68 counter packets 1 bytes 336 accept
oifname "virbr0" tcp dport 68 counter packets 0 bytes 0 accept
oifname "virbr1" udp dport 53 counter packets 0 bytes 0 accept
oifname "virbr1" tcp dport 53 counter packets 0 bytes 0 accept
oifname "virbr1" udp dport 68 counter packets 0 bytes 0 accept
oifname "virbr1" tcp dport 68 counter packets 0 bytes 0 accept
}
I'm wondering if these DHCP and DNS rules are in fact pointless.
In iptables, there's 1 set of global tables, and other firewall
tools or sysadmin might have put a DENY/REJECT that catches
DHCP/DNS. We inserted libvirt rules at the head of the tables,
so we can then explicitly ACCEPT DHCP/DNS, even if later rules
would deny them. So the LIBVIRT_INP/LIBVIRT_OUT rules are useful
in the context of iptables.
In nftables, there are arbitrary many tables, and a packet needs
to be allowed by *all* the tables, to continue its flow.
If a non-libvirt tables has put in a DENY/REJECT that catches
DHCP/DNS, then no matter what rules we put in the 'libvirt'
tables, we can never undo that DENY/REJECT.
So these LIBVIRT_INP/LIBVIRT_OUT rules are entirely pointless
unless the 'libvirt' table had later rules that could be
DENY/REJECTing DHCP/DNS. We don't today.
The only way I see these DHCP/DNS rules being useful, is if
the LIBVIRT_INP chain had a default 'deny' rule for 'virbr0',
to block the guest from all access to the host. That would
to some extent overlap with a general host firewall tool,
but there might not be one.
Currently our "isolated" config still allows guests to access
the host, just won't route off host. I guess any of the forward
modes could conceptually have a "deny host" access rule.
Still, even if we implemented this "deny host" concept, we
still don't need to add these DHCP/DNS rules to LIBVIRT_INP
and LIBVIRT_OUT, unless 'deny host' is actually active.
IOW, I think we should delete (or comment out) all the DHCP/DNS
rules from your nftables impl currently.
This all makes sense. I'll try it out early next week along with the
changes to table/chain naming you suggested yesterday. (I would say
"this weekend", but it's springtime, which means "end of year" parties
are happening everywhere, and we have 3 of them we have to go to just
this weekend :-/)
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