flannel crash when using a ppp0 modem interface

[jswantek]

Expected Behavior

When having a ppp0 modem interface on my Linux system flannel should not crash when parsing address on startup.

Current Behavior

When starting flannel if a ppp0 modem interface exists in my Linux system, flannel crashes with the following panic when parsing addresses:

I0624 23:06:59.293981   24938 flannel.go:92] Determining IP address of default interface
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1a31f90]

goroutine 20887 [running]:
github.com/rancher/k3s/vendor/github.com/vishvananda/netlink.parseAddr(0x400648bdec, 0x40, 0x40, 0x0, 0x400867a0a8, 0x4, 0x280, 0x0, 0x0, 0x400648be00, ...)
        /go/src/github.com/rancher/k3s/vendor/github.com/vishvananda/netlink/addr_linux.go:274 +0x170
github.com/rancher/k3s/vendor/github.com/vishvananda/netlink.(*Handle).AddrList(0x6721590, 0x43eff40, 0x400f0859e0, 0x2, 0x0, 0x4, 0x2bc, 0xfe, 0x1)
        /go/src/github.com/rancher/k3s/vendor/github.com/vishvananda/netlink/addr_linux.go:199 +0x180
github.com/rancher/k3s/vendor/github.com/vishvananda/netlink.AddrList(...)
        /go/src/github.com/rancher/k3s/vendor/github.com/vishvananda/netlink/addr_linux.go:174
github.com/rancher/k3s/vendor/github.com/coreos/flannel/pkg/ip.getIfaceAddrs(0x400e1e22c0, 0x0, 0x0, 0x0, 0x0, 0x0)
        /go/src/github.com/rancher/k3s/vendor/github.com/coreos/flannel/pkg/ip/iface.go:36 +0x68
github.com/rancher/k3s/vendor/github.com/coreos/flannel/pkg/ip.GetIfaceIP4Addr(0x400e1e22c0, 0x0, 0x0, 0x400775ee08, 0x1, 0x1)
        /go/src/github.com/rancher/k3s/vendor/github.com/coreos/flannel/pkg/ip/iface.go:40 +0x30
github.com/rancher/k3s/pkg/agent/flannel.LookupExtIface(0x400e1e22c0, 0x75ff34, 0x400cd82f08, 0x75f90c)
        /go/src/github.com/rancher/k3s/pkg/agent/flannel/flannel.go:100 +0xa8
github.com/rancher/k3s/pkg/agent/flannel.flannel(0x444d740, 0x4000e58c00, 0x0, 0x4006a5dd40, 0x34, 0x400b2e43f0, 0x2d, 0x1, 0x0)
        /go/src/github.com/rancher/k3s/pkg/agent/flannel/flannel.go:43 +0x28
github.com/rancher/k3s/pkg/agent/flannel.Run.func1(0x444d740, 0x4000e58c00, 0x4005df4380)
        /go/src/github.com/rancher/k3s/pkg/agent/flannel/setup.go:98 +0x5c
created by github.com/rancher/k3s/pkg/agent/flannel.Run
        /go/src/github.com/rancher/k3s/pkg/agent/flannel/setup.go:97 +0x290

Possible Solution

https://github.com/vishvananda/netlink/pull/665

Steps to Reproduce (for bugs)

1. Attach modem to USB port and wait for it to enumerate (have no other internet uplink interfaces) (Note: must enumerates as a ppp0 device.)
2. start flannel (potentially through a service such as k3s)

Context

• I have a Linux machine that will have (as it's sole connection to the Internet) a modem that enumerates as a ppp device and need to be able to run k3s on that system.
• This issue will not occur with modems that enumerate as wwan0 devices using the qmi_wwan driver (or equivalent)
• Issue also reported against:k3s (see: https://github.com/k3s-io/k3s/issues/3512)
• Issue also reported against: vishvananda/netlink (see: https://github.com/vishvananda/netlink/issues/664)
• Issue also reported against: kubernetes (see: https://github.com/kubernetes/kubernetes/issues/103280)

Your Environment

• Flannel version: flannel version within k3s version: v1.20.2+k3s1 (1d4adb0)
• Backend used (e.g. vxlan or udp): vxlan
• Etcd version:
• Kubernetes version (if used): k3s version: v1.20.2+k3s1 (1d4adb0)
• Operating System and version:

Linux ws-nxcore-000048B02D0766CD 4.9.140-tegra #1 SMP PREEMPT Thu Jun 17 21:46:37 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.5 LTS
Release:	18.04
Codename:	bionic

• Link to your project (optional):

[jswantek]

The proposed solution https://github.com/vishvananda/netlink/pull/665 does address the immediate panic but it was later discovered that lacking an IFA_ADDRESS (which can be easily seen using https://github.com/Yourens/rtnetlinkexample/blob/master/if_show.c) results in other downstream problems.

Jun 29 21:16:36 ws-nxcore-000048B02D0766CD bash[4543]: E0629 21:16:36.736218    4543 remote_runtime.go:116] RunPodSandbox from runtime service failed: rpc error: code = Unknown desc = failed to setup network for sandbox "c246d0f2899b3a6c0e83c2e03fafcebbd5ada9eb54f349c970142127624fb83a": netplugin failed with no error message
Jun 29 21:16:36 ws-nxcore-000048B02D0766CD bash[4543]: E0629 21:16:36.739284    4543 kuberuntime_sandbox.go:70] CreatePodSandbox for pod "coredns-854c77959c-8p7nv_kube-system(0295c50f-8c65-42ef-964e-b97cee322658)" failed: rpc error: code = Unknown desc = failed to setup network for sandbox "c246d0f2899b3a6c0e83c2e03fafcebbd5ada9eb54f349c970142127624fb83a": netplugin failed with no error message
Jun 29 21:16:36 ws-nxcore-000048B02D0766CD bash[4543]: E0629 21:16:36.739356    4543 kuberuntime_manager.go:755] createPodSandbox for pod "coredns-854c77959c-8p7nv_kube-system(0295c50f-8c65-42ef-964e-b97cee322658)" failed: rpc error: code = Unknown desc = failed to setup network for sandbox "c246d0f2899b3a6c0e83c2e03fafcebbd5ada9eb54f349c970142127624fb83a": netplugin failed with no error message
Jun 29 21:16:36 ws-nxcore-000048B02D0766CD bash[4543]: E0629 21:16:36.739554    4543 pod_workers.go:191] Error syncing pod 0295c50f-8c65-42ef-964e-b97cee322658 ("coredns-854c77959c-8p7nv_kube-system(0295c50f-8c65-42ef-964e-b97cee322658)"), skipping: failed to "CreatePodSandbox" for "coredns-854c77959c-8p7nv_kube-system(0295c50f-8c65-42ef-964e-b97cee322658)" with CreatePodSandboxError: "CreatePodSandbox for pod \"coredns-854c77959c-8p7nv_kube-system(0295c50f-8c65-42ef-964e-b97cee322658)\" failed: rpc error: code = Unknown desc = failed to setup network for sandbox \"c246d0f2899b3a6c0e83c2e03fafcebbd5ada9eb54f349c970142127624fb83a\": netplugin failed with no error message"

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