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net/dnscache, net/tsdial: add DNS caching to tsdial UserDial

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This is enough to handle the DNS queries as generated by Go's
net package (which our HTTP/SOCKS client uses), and the responses
generated by the ExitDNS DoH server.

This isn't yet suitable for putting on 100.100.100.100 where a number
of different DNS clients would hit it, as this doesn't yet do
EDNS0. It might work, but it's untested and likely incomplete.

Likewise, this doesn't handle anything about truncation, as the
exchanges are entirely in memory between Go or DoH. That would also
need to be handled later, if/when it's hooked up to 100.100.100.100.

Updates #3507

Change-Id: I1736b0ad31eea85ea853b310c52c5e6bf65c6e2a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2021-12-06 14:41:30 -08:00
committed by Brad Fitzpatrick
parent b59e7669c1
commit 39ffa16853
8 changed files with 649 additions and 9 deletions
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24
net/tsdial/tsdial.go
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@@ -11,6 +11,7 @@ import (
"fmt"
"net"
"net/http"
"runtime"
"strings"
"sync"
"sync/atomic"
@@ -18,6 +19,7 @@ import (
"time"
"inet.af/netaddr"
"tailscale.com/net/dnscache"
"tailscale.com/net/netknob"
"tailscale.com/types/netmap"
"tailscale.com/wgengine/monitor"
@@ -48,7 +50,8 @@ type Dialer struct {
dns dnsMap
tunName string // tun device name
linkMon *monitor.Mon
exitDNSDoHBase string // non-empty if DoH-proxying exit node in use; base URL+path (without '?')
exitDNSDoHBase string // non-empty if DoH-proxying exit node in use; base URL+path (without '?')
dnsCache *dnscache.MessageCache // nil until first first non-empty SetExitDNSDoH
}
// SetTUNName sets the name of the tun device in use ("tailscale0", "utun6",
@@ -76,7 +79,16 @@ func (d *Dialer) TUNName() string {
func (d *Dialer) SetExitDNSDoH(doh string) {
d.mu.Lock()
defer d.mu.Unlock()
if d.exitDNSDoHBase == doh {
return
}
d.exitDNSDoHBase = doh
if doh != "" && d.dnsCache == nil {
d.dnsCache = new(dnscache.MessageCache)
}
if d.dnsCache != nil {
d.dnsCache.Flush()
}
}
func (d *Dialer) SetLinkMonitor(mon *monitor.Mon) {
@@ -149,12 +161,14 @@ func (d *Dialer) userDialResolve(ctx context.Context, network, addr string) (net
}
var r net.Resolver
if exitDNSDoH != "" {
if exitDNSDoH != "" && runtime.GOOS != "windows" { // Windows: https://github.com/golang/go/issues/33097
r.PreferGo = true
r.Dial = func(ctx context.Context, network, address string) (net.Conn, error) {
return &dohConn{
ctx: ctx,
baseURL: exitDNSDoH,
hc: d.PeerAPIHTTPClient(),
ctx: ctx,
baseURL: exitDNSDoH,
hc: d.PeerAPIHTTPClient(),
dnsCache: d.dnsCache,
}, nil
}
}