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net/dns/resolver: return SERVFAIL when no upstream resolvers set 

Otherwise we just keep looping over the same thing again and again.

```
dns udp query: upstream nameservers not set
dns udp query: upstream nameservers not set
dns udp query: upstream nameservers not set
```

Signed-off-by: Maisem Ali <maisem@tailscale.com>
This commit is contained in:
Maisem Ali 2022-08-09 07:33:45 -07:00 committed by Maisem Ali
parent 0f12ead567
commit 4497bb0b81
1 changed files with 13 additions and 4 deletions
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17
net/dns/resolver/forwarder.go
View File

@ -76,8 +76,6 @@ const (
wellKnownHostBackupDelay = 200 * time.Millisecond
)
var errNoUpstreams = errors.New("upstream nameservers not set")
// txid identifies a DNS transaction.
//
// As the standard DNS Request ID is only 16 bits, we extend it:
@ -205,7 +203,7 @@ type forwarder struct {
//
// That is, if we're running on GCP or AWS where there's always a well-known
// IP of a recursive resolver, return that rather than having callers return
// errNoUpstreams. This fixes both normal 100.100.100.100 resolution when
// SERVFAIL. This fixes both normal 100.100.100.100 resolution when
// /etc/resolv.conf is missing/corrupt, and the peerapi ExitDNS stub
// resolver lookup.
cloudHostFallback []resolverAndDelay
@ -698,7 +696,18 @@ func (f *forwarder) forwardWithDestChan(ctx context.Context, query packet, respo
resolvers = f.resolvers(domain)
if len(resolvers) == 0 {
metricDNSFwdErrorNoUpstream.Add(1)
return errNoUpstreams
f.logf("no upstream resolvers set, returning SERVFAIL")
res, err := servfailResponse(query)
if err != nil {
f.logf("building servfail response: %v", err)
return nil
}
select {
case <-ctx.Done():
return ctx.Err()
case responseChan <- res:
return nil
}
}
}