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appc,ipn/ipnlocal: log DNS parsing errors in app connectors (#14607)

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If we fail to parse the upstream DNS response in an app connector, we
might miss new IPs for the target domain. Log parsing errors to be able
to diagnose that.

Updates #14606

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
This commit is contained in:
Andrew Lytvynov
2025-01-23 09:03:56 -08:00
committed by GitHub
parent a00623e8c4
commit f1710f4a42
5 changed files with 78 additions and 35 deletions
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21
appc/appconnector.go
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@@ -374,13 +374,13 @@ func (e *AppConnector) DomainRoutes() map[string][]netip.Addr {
// response is being returned over the PeerAPI. The response is parsed and
// matched against the configured domains, if matched the routeAdvertiser is
// advised to advertise the discovered route.
func (e *AppConnector) ObserveDNSResponse(res []byte) {
func (e *AppConnector) ObserveDNSResponse(res []byte) error {
var p dnsmessage.Parser
if _, err := p.Start(res); err != nil {
return
return err
}
if err := p.SkipAllQuestions(); err != nil {
return
return err
}
// cnameChain tracks a chain of CNAMEs for a given query in order to reverse
@@ -399,12 +399,12 @@ func (e *AppConnector) ObserveDNSResponse(res []byte) {
break
}
if err != nil {
return
return err
}
if h.Class != dnsmessage.ClassINET {
if err := p.SkipAnswer(); err != nil {
return
return err
}
continue
}
@@ -413,7 +413,7 @@ func (e *AppConnector) ObserveDNSResponse(res []byte) {
case dnsmessage.TypeCNAME, dnsmessage.TypeA, dnsmessage.TypeAAAA:
default:
if err := p.SkipAnswer(); err != nil {
return
return err
}
continue
@@ -427,7 +427,7 @@ func (e *AppConnector) ObserveDNSResponse(res []byte) {
if h.Type == dnsmessage.TypeCNAME {
res, err := p.CNAMEResource()
if err != nil {
return
return err
}
cname := strings.TrimSuffix(strings.ToLower(res.CNAME.String()), ".")
if len(cname) == 0 {
@@ -441,20 +441,20 @@ func (e *AppConnector) ObserveDNSResponse(res []byte) {
case dnsmessage.TypeA:
r, err := p.AResource()
if err != nil {
return
return err
}
addr := netip.AddrFrom4(r.A)
mak.Set(&addressRecords, domain, append(addressRecords[domain], addr))
case dnsmessage.TypeAAAA:
r, err := p.AAAAResource()
if err != nil {
return
return err
}
addr := netip.AddrFrom16(r.AAAA)
mak.Set(&addressRecords, domain, append(addressRecords[domain], addr))
default:
if err := p.SkipAnswer(); err != nil {
return
return err
}
continue
}
@@ -485,6 +485,7 @@ func (e *AppConnector) ObserveDNSResponse(res []byte) {
e.scheduleAdvertisement(domain, toAdvertise...)
}
}
return nil
}
// starting from the given domain that resolved to an address, find it, or any