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feature/conn25: preserve TTL on DNS rewrites

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We were accidentally hardcoding TTL 0 before.

Fixes tailscale/corp#45025

Signed-off-by: Michael Ben-Ami <mzb@tailscale.com>
This commit is contained in:
Michael Ben-Ami 2026-07-16 15:22:11 -04:00 committed by mzbenami
parent cfd101f9d7
commit 7ec9b7ffa3
2 changed files with 102 additions and 7 deletions
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14
feature/conn25/conn25.go
View File

@ -1069,9 +1069,9 @@ func (e *extension) sendAddressAssignment(ctx context.Context, as addrs) (tailcf
}
type dnsResponseRewrite struct {
domain dnsname.FQDN
dst netip.Addr
ttl time.Duration
domain dnsname.FQDN
dst netip.Addr
ttlSeconds uint32
}
func makeServFail(logf logger.Logf, h dnsmessage.Header, q dnsmessage.Question) []byte {
@ -1263,7 +1263,7 @@ func (c *Conn25) mapDNSResponse(buf []byte) []byte {
}
dstAddr = netip.AddrFrom16(r.AAAA)
}
answers = append(answers, dnsResponseRewrite{domain: queriedDomain, dst: dstAddr, ttl: time.Second * time.Duration(h.TTL)})
answers = append(answers, dnsResponseRewrite{domain: queriedDomain, dst: dstAddr, ttlSeconds: h.TTL})
default:
// we already checked the question was for a supported type, this answer is unexpected
if err := p.SkipAnswer(); err != nil {
@ -1297,7 +1297,7 @@ func (c *client) rewriteDNSResponse(appName string, hdr dnsmessage.Header, quest
// make an answer for each rewrite
for _, rw := range answers {
as, err := c.reserveAddresses(appName, rw.domain, rw.dst, rw.ttl)
as, err := c.reserveAddresses(appName, rw.domain, rw.dst, time.Duration(rw.ttlSeconds)*time.Second)
if err != nil {
return nil, err
}
@ -1309,12 +1309,12 @@ func (c *client) rewriteDNSResponse(appName string, hdr dnsmessage.Header, quest
return nil, err
}
if rw.dst.Is4() {
rhdr := dnsmessage.ResourceHeader{Name: name, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET, TTL: 0}
rhdr := dnsmessage.ResourceHeader{Name: name, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET, TTL: rw.ttlSeconds}
if err := b.AResource(rhdr, dnsmessage.AResource{A: as.magic.As4()}); err != nil {
return nil, err
}
} else if rw.dst.Is6() {
rhdr := dnsmessage.ResourceHeader{Name: name, Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET, TTL: 0}
rhdr := dnsmessage.ResourceHeader{Name: name, Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET, TTL: rw.ttlSeconds}
if err := b.AAAAResource(rhdr, dnsmessage.AAAAResource{AAAA: as.magic.As16()}); err != nil {
return nil, err
}

95
feature/conn25/conn25_test.go
View File

@ -1272,6 +1272,101 @@ func TestMapDNSResponseSetsExpiryBasedOnTTL(t *testing.T) {
}
func TestMapDNSResponsePreservesTTL(t *testing.T) {
configuredDomain := "example.com"
domainName := configuredDomain + "."
dnsMessageName := dnsmessage.MustNewName(domainName)
sn := makeSelfNode(t, []appctype.Conn25Attr{{
Name: "app1",
Connectors: []string{"tag:connector"},
Domains: []string{configuredDomain},
}}, appctype.Conn25PoolsAttr{
V4MagicIPPool: []netipx.IPRange{v4RangeFrom("0", "10")},
V4TransitIPPool: []netipx.IPRange{v4RangeFrom("40", "50")},
V6MagicIPPool: []netipx.IPRange{netipx.IPRangeFrom(netip.MustParseAddr("2606:4700::6812:100"), netip.MustParseAddr("2606:4700::6812:1ff"))},
V6TransitIPPool: []netipx.IPRange{netipx.IPRangeFrom(netip.MustParseAddr("2606:4700::6813:100"), netip.MustParseAddr("2606:4700::6813:1ff"))},
}, nil)
cfg := mustConfig(t, sn)
const wantTTL uint32 = 300
for _, tt := range []struct {
name string
toMap []byte
}{
{
name: "typeA",
toMap: makeDNSResponseForSections(t,
[]dnsmessage.Question{{Name: dnsMessageName, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET}},
[]dnsmessage.Resource{{
Header: dnsmessage.ResourceHeader{Name: dnsMessageName, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET, TTL: wantTTL},
Body: &dnsmessage.AResource{A: netip.MustParseAddr("1.2.3.4").As4()},
}},
nil,
),
},
{
name: "typeAAAA",
toMap: makeDNSResponseForSections(t,
[]dnsmessage.Question{{Name: dnsMessageName, Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET}},
[]dnsmessage.Resource{{
Header: dnsmessage.ResourceHeader{Name: dnsMessageName, Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET, TTL: wantTTL},
Body: &dnsmessage.AAAAResource{AAAA: netip.MustParseAddr("2606:4700::6812:1a78").As16()},
}},
nil,
),
},
{
// Use the TTL in the A record, not the CNAME.
name: "typeA-cname-chain",
toMap: makeDNSResponseForSections(t,
[]dnsmessage.Question{{Name: dnsMessageName, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET}},
[]dnsmessage.Resource{
{
Header: dnsmessage.ResourceHeader{Name: dnsMessageName, Type: dnsmessage.TypeCNAME, Class: dnsmessage.ClassINET, TTL: wantTTL + 999},
Body: &dnsmessage.CNAMEResource{CNAME: dnsmessage.MustNewName("cdn.example.net.")},
},
{
Header: dnsmessage.ResourceHeader{Name: dnsmessage.MustNewName("cdn.example.net."), Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET, TTL: wantTTL},
Body: &dnsmessage.AResource{A: netip.MustParseAddr("1.2.3.4").As4()},
},
},
nil,
),
},
{
// Use the TTL in the AAAA record, not the CNAME.
name: "typeAAAA-cname-chain",
toMap: makeDNSResponseForSections(t,
[]dnsmessage.Question{{Name: dnsMessageName, Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET}},
[]dnsmessage.Resource{
{
Header: dnsmessage.ResourceHeader{Name: dnsMessageName, Type: dnsmessage.TypeCNAME, Class: dnsmessage.ClassINET, TTL: wantTTL + 999},
Body: &dnsmessage.CNAMEResource{CNAME: dnsmessage.MustNewName("cdn.example.net.")},
},
{
Header: dnsmessage.ResourceHeader{Name: dnsmessage.MustNewName("cdn.example.net."), Type: dnsmessage.TypeAAAA, Class: dnsmessage.ClassINET, TTL: wantTTL},
Body: &dnsmessage.AAAAResource{AAAA: netip.MustParseAddr("2606:4700::6812:1a78").As16()},
},
},
nil,
),
},
} {
t.Run(tt.name, func(t *testing.T) {
c := newConn25(logger.Discard)
c.reconfig(cfg)
answers, _ := parseResponse(t, c.mapDNSResponse(tt.toMap))
if len(answers) != 1 {
t.Fatalf("got %d answers, want 1", len(answers))
}
if got := answers[0].Header.TTL; got != wantTTL {
t.Fatalf("rewritten answer TTL = %d, want %d", got, wantTTL)
}
})
}
}
func TestNormalizedDNSNames(t *testing.T) {
tests := []struct {
name string