XFRM Interface Development Notes
Development notes for XFRMi
libreswan/pluto design choices
- allow names ipsec0, ipsec1 ... ipsecx.
- Should we allow names other than ipsecXX ?
- initial thought is keep "xfrm interface id" and "xfrm output mark" consistent.
- interface creation is inside pluto.
- create bugzilla entry for Fedora/CentOS kernels? Fedora 28 do not enable
XFRM INTERFACE
Commit cover letter from Steffen 20180612, Merged in 4.19:
https://patchwork.ozlabs.org/cover/928175/ Steffen Klassert June 12, 2018, 7:56 a.m. This patchset introduces new virtual xfrm interfaces. The design of virtual xfrm interfaces interfaces was discussed at the Linux IPsec workshop 2018. This patchset implements these interfaces as the IPsec userspace and kernel developers agreed. The purpose of these interfaces is to overcome the design limitations that the existing VTI devices have. The main limitations that we see with the current VTI are the following: - VTI interfaces are L3 tunnels with configurable endpoints. For xfrm, the tunnel endpoint are already determined by the SA. So the VTI tunnel endpoints must be either the same as on the SA or wildcards. In case VTI tunnel endpoints are same as on the SA, we get a one to one correlation between the SA and the tunnel. So each SA needs its own tunnel interface. On the other hand, we can have only one VTI tunnel with wildcard src/dst tunnel endpoints in the system because the lookup is based on the tunnel endpoints. The existing tunnel lookup won't work with multiple tunnels with wildcard tunnel endpoints. Some usecases require more than on VTI tunnel of this type, for example if somebody has multiple namespaces and every namespace requires such a VTI. - VTI needs separate interfaces for IPv4 and IPv6 tunnels. So when routing to a VTI, we have to know to which address family this traffic class is going to be encapsulated. This is a lmitation because it makes routing more complex and it is not always possible to know what happens behind the VTI, e.g. when the VTI is move to some namespace. - VTI works just with tunnel mode SAs. We need generic interfaces that ensures transfomation, regardless of the xfrm mode and the encapsulated address family. - VTI is configured with a combination GRE keys and xfrm marks. With this we have to deal with some extra cases in the generic tunnel lookup because the GRE keys on the VTI are actually not GRE keys, the GRE keys were just reused for something else. All extensions to the VTI interfaces would require to add even more complexity to the generic tunnel lookup. To overcome this, we started with the following design goal: - It should be possible to tunnel IPv4 and IPv6 through the same interface. - No limitation on xfrm mode (tunnel, transport and beet). - Should be a generic virtual interface that ensures IPsec transformation, no need to know what happens behind the interface. - Interfaces should be configured with a new key that must match a new policy/SA lookup key. - The lookup logic should stay in the xfrm codebase, no need to change or extend generic routing and tunnel lookups. - Should be possible to use IPsec hardware offloads of the underlying interface.
Initial xfrmi kernel commits
- Steffen Klassert's at Linux IPsec 2018, Dresden https://workshop.linux-ipsec.org/2018/slides/xfrm_interfaces.pdf
XFRM OUTPUT_MARK (required commits to be pulled to RHEL)
Add mask and rename to XFRMA_SET_MARK, Steffen
Which mark?
Two marks related to xfrm code in Linux kernel. XFRMA_MARK and XFRMA_SET_MARK(aka XFRMA_OUTPUT_MARK). Now on I use XFRM_OUTPUT_MARK mark which as of 4.20 mean XFRM_SET_MARK/XFRM_SET_MARK_MASK
One line difference between the two. XFRM_OUTPUT_MARK mark is for routing a packet after XFRM (think as ESP out or Clear text in), while XFRMA_MARK could be sees as routing a clear text packet into xfrm code, XFRMA_MARK is a lookup key of SPDB and SADB.
XFRMA_MARK is used inside xfrm code on for outgoing clear text packet Jamal's notes (clear text packet out only. I wonder why set XFRMA_MARK on incoming SA. See libreswan commit.
To be clear One could say both marks are used for routing a packet at different stages of it while to goes through Linux stack and get transformed inside XFRM. Again XFRM_SET_MARK it is used from routing say outgoing clear text packet. While XFRM_OUTPUT_MARK is used for routing ESP packet on the output side and clear text packet on the input side. You see a bit more details at Jamal's explanation
XFRMA_MARK - mark(u32)/mask(u32). XFRM_OUTPUT_MARK - mark(u32)/[mask(u32). So one difference is for XFRM_OUTPUT_MARK mask is optional as of 4.19, 4.18 did not support mask for OUTPUT_MARK.
Both marks are used by routing, IPsec and routing has to collaborate this. That why there is mask. One part for IPsec/XFRM and other for rest of the system to scrible. XFRM stack should pass on the mark. Masked part is opaque to xfrm. I know there two areas where this come to play. The second one yet to be tested.
use case of marks
- Simple use case XFRMI interface.
XFRM_OUTPUT_MARK by libreswan when the the other/peer end is inside the extruded tunnel. In other words. Say /32-to-/32 tunnel without NAT or 0.0.0.0/0 tunnel. Note it is adding rules to rout
ip rule add prio 100 to 192.1.2.23/32 not fwmark 1/0xffffffff lookup 50 ip route add table 50 192.1.2.23/32 dev ipsec0 src 192.1.3.209 <pre> * XFRMI interface and multihoming. Yet to test this. * Simple case IPsec and IP_VTI. Then you can pick any mask. in libreswan config you set mark=2/0xffffffff * A bit more complicated case VTI and multihoming Lets say you have two upstreams both route packets to your host. Then you would start to use commands like bellow. If you are familiar with those and use IPse in combination with linux IP_VTI support you may et of XFRMA_MARK (with mask. I will expand this one day. iptables -t mangle -N MARK-ISP1 iptables -t mangle -A MARK-ISP1 -j MARK --set-mark 1 iptables -t mangle -A MARK-ISP1 -j CONNMARK --save-mark iptables -t mangle -N MARK-ISP2 iptables -t mangle -A MARK-ISP2 -j MARK --set-mark 2 iptables -t mangle -A MARK-ISP2 -j CONNMARK --save-mark ip rule add fwmark 1 table ISP1 ip rule add fwmark 2 table ISP2 ip route add table ISP1 192.0.3.0/24 dev eth1 src 192.0.2.0/24 ip route add table ISP2 192.0.3.0/24 dev eth2 src 192.0.22.0/24
XFRM_OUTPUT_MARK is used by libreswan when the the other/peer end is inside the extruded tunnel. In other words. Say /32-to-/32 tunnel without NAT or 0.0.0.0/0 tunnel.
Fedora support
- F29 commit enabled it. However not in F28
- RHEL bugzilla request??