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101145742fThe dial-time SSRF guard runs on the resolved IP, so the tests that prove a symbolic hostname cannot reach loopback used "localhost." — a trailing dot never matches /etc/hosts, so Go queries real DNS. Machines whose resolver does not answer "localhost." (a VPN DNS, for example) got "no such host" before the dial guard ever ran, failing three specs. Add tests.StubResolver, a net.Resolver backed by an in-memory DNS responder over net.Pipe, and let the plugin dialers take a resolver so tests can inject it. Name resolution in those specs no longer depends on the machine's DNS.
54 lines
1.5 KiB
Go
54 lines
1.5 KiB
Go
package tests
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import (
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"context"
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"encoding/binary"
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"io"
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"net"
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"net/netip"
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"golang.org/x/net/dns/dnsmessage"
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)
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// StubResolver returns a net.Resolver that answers A queries from records (absolute name to IPv4,
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// e.g. "localhost." to "127.0.0.1") instead of the system DNS. Other names do not resolve.
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func StubResolver(records map[string]string) *net.Resolver {
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return &net.Resolver{
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PreferGo: true,
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Dial: func(context.Context, string, string) (net.Conn, error) {
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client, server := net.Pipe()
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go serveStubDNS(server, records)
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return client, nil
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},
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}
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}
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// net.Pipe is not a PacketConn, so the resolver sends one query framed with a 2-byte length prefix.
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func serveStubDNS(conn net.Conn, records map[string]string) {
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defer conn.Close()
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var size [2]byte
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if _, err := io.ReadFull(conn, size[:]); err != nil {
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return
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}
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buf := make([]byte, binary.BigEndian.Uint16(size[:]))
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if _, err := io.ReadFull(conn, buf); err != nil {
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return
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}
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var msg dnsmessage.Message
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if err := msg.Unpack(buf); err != nil || len(msg.Questions) != 1 {
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return
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}
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msg.Response = true
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q := msg.Questions[0]
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if ip, err := netip.ParseAddr(records[q.Name.String()]); err == nil && q.Type == dnsmessage.TypeA {
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msg.Answers = []dnsmessage.Resource{{
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Header: dnsmessage.ResourceHeader{Name: q.Name, Type: q.Type, Class: q.Class},
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Body: &dnsmessage.AResource{A: ip.As4()},
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}}
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}
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resp, err := msg.Pack()
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if err != nil {
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return
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}
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_, _ = conn.Write(append(binary.BigEndian.AppendUint16(nil, uint16(len(resp))), resp...))
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}
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