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cmd/sniproxy: draw the rest of the DNS owl.

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Add a DNS server which always responds as its own IP addresses.

Additionally add a tsnet TailscaleIPs() function to return the
IP addresses, both IPv4 and IPv6.

Updates https://github.com/tailscale/tailscale/issues/1748

Signed-off-by: Denton Gentry <dgentry@tailscale.com>
This commit is contained in:
Denton Gentry
2023-03-05 16:40:15 -08:00
committed by Denton Gentry
parent 7e6c5a2db4
commit b46c5ae82a
3 changed files with 143 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

88
cmd/sniproxy/snipproxy.go
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@@ -14,6 +14,7 @@ import (
"strings"
"time"
"golang.org/x/net/dns/dnsmessage"
"inet.af/tcpproxy"
"tailscale.com/client/tailscale"
"tailscale.com/net/netutil"
@@ -23,6 +24,8 @@ import (
var ports = flag.String("ports", "443", "comma-separated list of ports to proxy")
var tsMBox = dnsmessage.MustNewName("support.tailscale.com.")
func main() {
flag.Parse()
if *ports == "" {
@@ -86,8 +89,29 @@ func (s *server) serveDNSConn(c nettype.ConnPacketConn) {
c.SetReadDeadline(time.Now().Add(5 * time.Second))
buf := make([]byte, 1500)
n, err := c.Read(buf)
log.Printf("got DNS packet: %q, %v", buf[:n], err)
// TODO: rest of the owl
if err != nil {
log.Printf("c.Read failed: %v\n ", err)
return
}
var msg dnsmessage.Message
err = msg.Unpack(buf[:n])
if err != nil {
log.Printf("dnsmessage unpack failed: %v\n ", err)
return
}
buf, err = s.dnsResponse(&msg)
if err != nil {
log.Printf("s.dnsResponse failed: %v\n", err)
return
}
_, err = c.Write(buf)
if err != nil {
log.Printf("c.Write failed: %v\n", err)
return
}
}
func (s *server) serveConn(c net.Conn) {
@@ -107,7 +131,6 @@ func (s *server) serveConn(c net.Conn) {
return netutil.NewOneConnListener(c, nil), nil
}
p.AddSNIRouteFunc(addrPortStr, func(ctx context.Context, sniName string) (t tcpproxy.Target, ok bool) {
log.Printf("got req for %q from %v", sniName, c.RemoteAddr())
return &tcpproxy.DialProxy{
Addr: net.JoinHostPort(sniName, port),
DialContext: dialer.DialContext,
@@ -115,3 +138,62 @@ func (s *server) serveConn(c net.Conn) {
})
p.Start()
}
func (s *server) dnsResponse(req *dnsmessage.Message) (buf []byte, err error) {
resp := dnsmessage.NewBuilder(buf,
dnsmessage.Header{
ID: req.Header.ID,
Response: true,
Authoritative: true,
})
resp.EnableCompression()
if len(req.Questions) == 0 {
buf, _ = resp.Finish()
return
}
q := req.Questions[0]
err = resp.StartQuestions()
if err != nil {
return
}
resp.Question(q)
ip4, ip6 := s.ts.TailscaleIPs()
err = resp.StartAnswers()
if err != nil {
return
}
switch q.Type {
case dnsmessage.TypeAAAA:
err = resp.AAAAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.AAAAResource{AAAA: ip6.As16()},
)
case dnsmessage.TypeA:
err = resp.AResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.AResource{A: ip4.As4()},
)
case dnsmessage.TypeSOA:
err = resp.SOAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.SOAResource{NS: q.Name, MBox: tsMBox, Serial: 2023030600,
Refresh: 120, Retry: 120, Expire: 120, MinTTL: 60},
)
case dnsmessage.TypeNS:
err = resp.NSResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.NSResource{NS: tsMBox},
)
}
if err != nil {
return
}
return resp.Finish()
}