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net/dns/resolver: return symbolic PTR records for TS service IPs (#4361)

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Fixes #1233

Signed-off-by: Tom DNetto <tom@tailscale.com>

Co-authored-by: Tom DNetto <tom@tailscale.com>
This commit is contained in:
Tom 2022-04-06 15:56:21 -07:00 committed by GitHub
parent 0b273e1857
commit 6be7931eb4
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2 changed files with 24 additions and 0 deletions
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22
net/dns/resolver/tsdns.go
View File

@ -34,6 +34,8 @@ import (
"tailscale.com/wgengine/monitor"
)
const dnsSymbolicFQDN = "magicdns.localhost-tailscale-daemon."
// maxResponseBytes is the maximum size of a response from a Resolver. The
// actual buffer size will be one larger than this so that we can detect
// truncation in a platform-agnostic way.
@ -553,6 +555,18 @@ func (r *Resolver) resolveLocal(domain dnsname.FQDN, typ dns.Type) (netaddr.IP,
return netaddr.IP{}, dns.RCodeNameError
}
// We return a symbolic domain if someone does a reverse lookup on the
// DNS endpoint. To round out this special case, we also do the inverse
// (returning the endpoint IP if someone looks up the symbolic domain).
if domain == dnsSymbolicFQDN {
switch typ {
case dns.TypeA:
return tsaddr.TailscaleServiceIP(), dns.RCodeSuccess
case dns.TypeAAAA:
return tsaddr.TailscaleServiceIPv6(), dns.RCodeSuccess
}
}
r.mu.Lock()
hosts := r.hostToIP
localDomains := r.localDomains
@ -644,6 +658,14 @@ func (r *Resolver) resolveLocalReverse(name dnsname.FQDN) (dnsname.FQDN, dns.RCo
return "", dns.RCodeRefused
}
// If someone curiously does a reverse lookup on the DNS IP, we
// return a domain that helps indicate that Tailscale is using
// this IP for a special purpose and it is not a node on their
// tailnet.
if ip == tsaddr.TailscaleServiceIP() || ip == tsaddr.TailscaleServiceIPv6() {
return dnsSymbolicFQDN, dns.RCodeSuccess
}
r.mu.Lock()
defer r.mu.Unlock()
ret, ok := r.ipToHost[ip]

2
net/dns/resolver/tsdns_test.go
View File

@ -344,6 +344,7 @@ func TestResolveLocal(t *testing.T) {
{"mx-nxdomain", "test3.ipn.dev.", dns.TypeMX, netaddr.IP{}, dns.RCodeNameError},
{"ns-nxdomain", "test3.ipn.dev.", dns.TypeNS, netaddr.IP{}, dns.RCodeNameError},
{"onion-domain", "footest.onion.", dns.TypeA, netaddr.IP{}, dns.RCodeNameError},
{"magicdns", dnsSymbolicFQDN, dns.TypeA, netaddr.MustParseIP("100.100.100.100"), dns.RCodeSuccess},
}
for _, tt := range tests {
@ -377,6 +378,7 @@ func TestResolveLocalReverse(t *testing.T) {
{"ipv4_nxdomain", dnsname.FQDN("5.3.2.1.in-addr.arpa."), "", dns.RCodeNameError},
{"ipv6_nxdomain", dnsname.FQDN("0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.ip6.arpa."), "", dns.RCodeNameError},
{"nxdomain", dnsname.FQDN("2.3.4.5.in-addr.arpa."), "", dns.RCodeRefused},
{"magicdns", dnsname.FQDN("100.100.100.100.in-addr.arpa."), dnsSymbolicFQDN, dns.RCodeSuccess},
}
for _, tt := range tests {