Date: Sun, 2 Aug 2020 14:45:26 +0200 From: Miroslav Lachman <000.fbsd@quip.cz> To: freebsd-virtualization@freebsd.org Subject: Re: Restricting IP ranges for guests over tap devices Message-ID: <7acfc19f-f58f-ed55-0ed5-162c3ef23d87@quip.cz> In-Reply-To: <CACLnyCLNtcR0Aa2aO6hUMmW1S%2B41EdrhmtcfERJ3y2Lgxq_dcg@mail.gmail.com> References: <20200801145144.7bf342d9@sunflower.int.arc7.info> <CACLnyCLNtcR0Aa2aO6hUMmW1S%2B41EdrhmtcfERJ3y2Lgxq_dcg@mail.gmail.com>
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On 02/08/2020 03:36, Jason Tubnor wrote: > On Sun, 2 Aug 2020 at 00:51, Mark Raynsford via freebsd-virtualization < > freebsd-virtualization@freebsd.org> wrote: > >> Hello! >> >> Let's say I have a machine running a few dozen bhyve guests. Each bhyve >> guest gets its own tap device, and all of the tap devices are connected >> to a bridge. >> >> Everything works fine. I can write pf rules that control access between >> each guest, and between each guest and the world. I can't directly >> observe the IP addresses that the guests have assigned to the tap >> devices I gave them, but if I know the addresses beforehand, I can for >> example write pf rules that say things like: >> >> block log all >> pass in on tap23 proto tcp \ >> from any to $guest_23_ip port ssh modulate state >> >> That then means that even if the guest is compromised and tries to bind >> a server to another address, the pf rules won't allow anyone else to >> actually connect to it. >> >> The good thing about this is also the bad thing about this; I have to >> write specific rules that say "only allow access to this specific IP >> via this specific tap device". Over dozens of guests, that can multiply >> to hundreds of laboriously maintained rules. >> >> Is there some more general way I can supply a mapping between tap >> devices and allowed addresses? Remember that pf can't see the guest >> addresses on the host sides of the tap devices, so I can't use the >> (device) syntax to expand to "the address of a NIC called 'device'". >> >> >> > Treat the tap interface as a bridge and only define the destination port. > That way you are able to protect the guest from the host without knowing > the guest IP address. > > I'd do it a bit differently though. I'd treat the bridge that everything > is tapped into as being a hostile environment. As such, each guest would > protect itself as if you had a VPN on the public internet, using the guests > built-in firewall. > > Another way is isolating each guest or bunch of guests on private VLANs and > then protect these subnets on the host. For me the more serious issue is that malicious guest can assign IP of another guest or the main host and cause some collisions or malfunctions. I am looking for the right solution for a long time. Miroslav Lachman
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