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wgengine/tstun: reply to MagicDNS pings 

Fixes #849

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
(cherry picked from commit 917307a90c)
bradfitz/proposed-1.4.5
Brad Fitzpatrick 2021-02-11 11:51:59 -08:00
parent 90c249cf26
commit 31f2cd9e45
1 changed files with 10 additions and 0 deletions
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10
wgengine/tstun/tun.go
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@ -215,7 +215,17 @@ func (t *TUN) poll() {
}
}
var magicDNSIPPort = netaddr.MustParseIPPort("100.100.100.100:0")
func (t *TUN) filterOut(p *packet.Parsed) filter.Response {
// Fake ICMP echo responses to MagicDNS (100.100.100.100).
if p.IsEchoRequest() && p.Dst == magicDNSIPPort {
header := p.ICMP4Header()
header.ToResponse()
outp := packet.Generate(&header, p.Payload())
t.InjectInboundCopy(outp)
return filter.DropSilently // don't pass on to OS; already handled
}
if t.PreFilterOut != nil {
if res := t.PreFilterOut(p, t); res.IsDrop() {