86 lines
2.1 KiB
Go
86 lines
2.1 KiB
Go
package etcd
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import (
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"context"
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"errors"
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"github.com/coredns/coredns/plugin/pkg/log"
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"github.com/coredns/coredns/request"
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"github.com/miekg/dns"
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)
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// Stub wraps an Etcd. We have this type so that it can have a ServeDNS method.
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type Stub struct {
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*Etcd
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Zone string // for what zone (and thus what nameservers are we called)
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}
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// ServeDNS implements the plugin.Handler interface.
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func (s Stub) ServeDNS(ctx context.Context, w dns.ResponseWriter, req *dns.Msg) (int, error) {
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if hasStubEdns0(req) {
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log.Warningf("Forwarding cycle detected, refusing msg: %s", req.Question[0].Name)
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return dns.RcodeRefused, errors.New("stub forward cycle")
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}
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req = addStubEdns0(req)
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proxy, ok := (*s.Etcd.Stubmap)[s.Zone]
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if !ok { // somebody made a mistake..
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return dns.RcodeServerFailure, nil
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}
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state := request.Request{W: w, Req: req}
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m, e := proxy.Forward(state)
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if e != nil {
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return dns.RcodeServerFailure, e
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}
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m.RecursionAvailable, m.Compress = true, true
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state.SizeAndDo(m)
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w.WriteMsg(m)
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return dns.RcodeSuccess, nil
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}
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// hasStubEdns0 checks if the message is carrying our special edns0 zero option.
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func hasStubEdns0(m *dns.Msg) bool {
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option := m.IsEdns0()
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if option == nil {
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return false
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}
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for _, o := range option.Option {
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if o.Option() == ednsStubCode && len(o.(*dns.EDNS0_LOCAL).Data) == 1 &&
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o.(*dns.EDNS0_LOCAL).Data[0] == 1 {
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return true
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}
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}
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return false
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}
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// addStubEdns0 adds our special option to the message's OPT record.
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func addStubEdns0(m *dns.Msg) *dns.Msg {
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option := m.IsEdns0()
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// Add a custom EDNS0 option to the packet, so we can detect loops when 2 stubs are forwarding to each other.
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if option != nil {
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option.Option = append(option.Option, &dns.EDNS0_LOCAL{Code: ednsStubCode, Data: []byte{1}})
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return m
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}
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m.Extra = append(m.Extra, ednsStub)
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return m
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}
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const (
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ednsStubCode = dns.EDNS0LOCALSTART + 10
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stubDomain = "stub.dns"
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)
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var ednsStub = func() *dns.OPT {
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o := new(dns.OPT)
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o.Hdr.Name = "."
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o.Hdr.Rrtype = dns.TypeOPT
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o.SetUDPSize(4096)
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e := new(dns.EDNS0_LOCAL)
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e.Code = ednsStubCode
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e.Data = []byte{1}
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o.Option = append(o.Option, e)
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return o
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}()
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