Here is a rough sketch:
type allowedIPsListener struct {
allowed []net.IP
inner net.Listener
}
func (ln *allowedIPsListener) Accept() (net.Conn, error) {
for {
conn, err := ln.inner.Accept()
if err != nil {
return nil, err
}
if !ln.allowed(conn.RemoteAddr()) {
conn.Close()
continue
}
return conn, nil
}
}
func (ln *allowedIPsListener) Close() error {
return ln.inner.Close()
}
func (ln *allowedIPsListener) Addr() net.Addr {
return ln.inner.Addr()
}
func (ln *allowedIPsListener) allowed(addr net.Addr) bool {
// TODO: implement
return true
}
Then, to use:
ln, err := net.Listen("tcp", addr)
if err != nil {
log.Fatal(err)
}
aln := &allowedIPsListener{allowed: yourListOfIPs, inner: ln}
tlsln := tls.NewListener(aln, yourTLSConfig)
// use tlsln
On 3/15/19 2:58 PM, Glen Huang wrote:
> Thanks for the quick reply.
>
> I want to use tcp, is it possible to leverage TCPListener or I have to
> invent my own? It seems I'll face the same issue as I do with tls?
>
> On Friday, March 15, 2019 at 9:46:00 PM UTC+8, Andrei Tudor Călin wrote:
>>
>> Begin by implementing a `net.Listener` which checks the list of allowed
>> IPs.
>> You'll be able to run code before the connection is passed on to
>> crypto/tls.
>> Wrap it using https://golang.org/pkg/crypto/tls/#NewListener.
>>
>> On 3/15/19 2:10 PM, Glen Huang wrote:
>>> I'm trying to limit which clients are allowed to connect to my tls
>> server
>>> by their IPs.
>>>
>>> I know I can do that after Accept, check their IPs and close the
>> connection
>>> if they're not whitelisted. But that means the full tls handshake has to
>>> complete before I can do that.
>>>
>>> Another option is that I can use nftables to whitelist clients at the
>>> kernel level. But to do that, I either have to spawn a subprocess to
>> call
>>> nft, which is kinda slow or use google/nftables that isn't production
>> ready
>>> yet (also missing some features I need).
>>>
>>> Is there anyway I can drop the tls connection when a client sends SYN?
>>>
>>> Thanks in advance.
>>>
>>
>> --
>> Andrei Tudor Călin
>>
>
--
Andrei Tudor Călin
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