bug: TestDERPEndToEnd : NPE if nil Region in derpmap #11202
Description
Seen here: https://github.com/coder/coder/actions/runs/7206571800/job/19631681483
2023-12-14T09:01:17.9425955Z t.go:84: 2023-12-14 09:00:51.289 [debu] servertailnet: updating derp map derp_map="&{HomeParams:<nil> Regions:map[10001:<nil>] OmitDefaultRegions:true}"
2023-12-14T09:01:17.9427048Z t.go:84: 2023-12-14 09:00:51.289 [debu] servertailnet.net.wgengine: magicsock: closing connection to derp-999 (derp-region-redefined), age 5s
2023-12-14T09:01:17.9427853Z t.go:84: 2023-12-14 09:00:51.289 [debu] servertailnet.net.wgengine: magicsock: 0 active derp conns
2023-12-14T09:01:17.9428485Z t.go:84: 2023-12-14 09:00:51.289 [debu] servertailnet: updating network map
2023-12-14T09:01:17.9429643Z t.go:84: 2023-12-14 09:00:51.289 [debu] servertailnet.net.netstack: [v2] netstack: registered IP fd7a:115c:a1e0:4713:8699:733c:9786:1b27/128
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x30 pc=0x10b890d]
goroutine 74133 [running]:
tailscale.com/net/netcheck.sortRegions(0xc093820c18, 0xc08cc5a9a0)
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/net/netcheck/netcheck.go:379 +0xed
tailscale.com/net/netcheck.makeProbePlan(0xc093f2af88?, 0xc095118d20?, 0xc08cc5a9a0)
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/net/netcheck/netcheck.go:422 +0xea
tailscale.com/net/netcheck.(*Client).GetReport(0xc088053c80, {0x3af14a8, 0xc08d8bd6c0}, 0xc093820c18)
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/net/netcheck/netcheck.go:981 +0xfde
tailscale.com/wgengine/magicsock.(*Conn).updateNetInfo(0xc08a069500, {0x3af[1438](https://github.com/coder/coder/actions/runs/7206571800/job/19631681483#step:5:1439), 0xc08d75ccd0})
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/wgengine/magicsock/magicsock.go:642 +0x1e5
tailscale.com/wgengine/magicsock.(*Conn).determineEndpoints(0xc08a069500, {0x3af1438, 0xc08d75ccd0})
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/wgengine/magicsock/magicsock.go:840 +0x85
tailscale.com/wgengine/magicsock.(*Conn).updateEndpoints(0xc08a069500, {0x2bfdf54, 0xf})
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/wgengine/magicsock/magicsock.go:549 +0x249
created by tailscale.com/wgengine/magicsock.(*Conn).ReSTUN in goroutine 74131
/home/runner/go/pkg/mod/github.com/coder/tailscale@v1.1.1-0.20231205095743-61c97bad8c8b/wgengine/magicsock/magicsock.go:2215 +0x3ee
Context in netcheck.go:
// sortRegions returns the regions of dm first sorted
// from fastest to slowest (based on the 'last' report),
// end in regions that have no data.
func sortRegions(dm *tailcfg.DERPMap, last *Report) (prev []*tailcfg.DERPRegion) {
prev = make([]*tailcfg.DERPRegion, 0, len(dm.Regions))
for _, reg := range dm.Regions {
if reg.Avoid { // <-- explosion here
continue
}
prev = append(prev, reg)
}