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refactor: expose the DNS database functionality (#27)
Reusing this code will help to implement DNS poisoning.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,179 @@ | ||
| // SPDX-License-Identifier: GPL-3.0-or-later | ||
|
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||
| // Package models the distributed DNS database. | ||
| package dns | ||
|
|
||
| import ( | ||
| "net" | ||
|
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| "github.com/miekg/dns" | ||
| "github.com/rbmk-project/common/runtimex" | ||
| "github.com/rbmk-project/dnscore/dnscoretest" | ||
| ) | ||
|
|
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| // Handler is an alias for dnscoretest.Handler. | ||
| type Handler = dnscoretest.Handler | ||
|
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| // Database models the global DNS database. | ||
| type Database struct { | ||
| names map[string][]dns.RR | ||
| } | ||
|
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| // NewDatabase creates a new DNS database. | ||
| func NewDatabase() *Database { | ||
| return &Database{ | ||
| names: make(map[string][]dns.RR), | ||
| } | ||
| } | ||
|
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| // AddCNAME adds a CNAME alias. | ||
| // | ||
| // This method IS NOT goroutine safe. | ||
| func (dd *Database) AddCNAME(name, alias string) { | ||
| header := dns.RR_Header{ | ||
| Name: dns.CanonicalName(name), | ||
| Rrtype: dns.TypeCNAME, | ||
| Class: dns.ClassINET, | ||
| Ttl: 3600, | ||
| Rdlength: 0, | ||
| } | ||
|
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| rr := &dns.CNAME{ | ||
| Hdr: header, | ||
| Target: dns.CanonicalName(alias), | ||
| } | ||
|
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| dd.names[name] = append(dd.names[name], rr) | ||
| } | ||
|
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| // AddAddresses adds A/AAAA records mapping the given | ||
| // domainNames to the given IPv4/IPv6 addresses. | ||
| // | ||
| // This method IS NOT goroutine safe. | ||
| func (dd *Database) AddAddresses(domainNames, addresses []string) { | ||
| for _, name := range domainNames { | ||
| name = dns.CanonicalName(name) | ||
| for _, addr := range addresses { | ||
| // Make sure the string is a valid IP address | ||
| ipAddr := net.ParseIP(addr) | ||
| runtimex.Assert(ipAddr != nil, "invalid IP address") | ||
|
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| // Create the common DNS header | ||
| header := dns.RR_Header{ | ||
| Name: dns.CanonicalName(name), | ||
| Rrtype: 0, | ||
| Class: dns.ClassINET, | ||
| Ttl: 3600, | ||
| Rdlength: 0, | ||
| } | ||
|
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| // Create the DNS record to add | ||
| var rr dns.RR | ||
| switch ipAddr.To4() { | ||
| case nil: | ||
| header.Rrtype = dns.TypeAAAA | ||
| rr = &dns.AAAA{Hdr: header, AAAA: ipAddr} | ||
| default: | ||
| header.Rrtype = dns.TypeA | ||
| rr = &dns.A{Hdr: header, A: ipAddr} | ||
| } | ||
|
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| dd.names[name] = append(dd.names[name], rr) | ||
| } | ||
| } | ||
| } | ||
|
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| // Ensure [*dnsDatabase] implements [dnsHandler]. | ||
| var _ Handler = (*Database)(nil) | ||
|
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| // Handler implements [dnsHandler] using [*dnsDatabase]. | ||
| // | ||
| // This method is goroutine safe as long as one does not | ||
| // modify the database while handling queries. | ||
| func (dd *Database) Handle(rw dnscoretest.ResponseWriter, rawQuery []byte) { | ||
| // Parse the incoming query and make sure it's a | ||
| // query containing just one question. | ||
| var ( | ||
| response = &dns.Msg{} | ||
| query = &dns.Msg{} | ||
| ) | ||
| if err := query.Unpack(rawQuery); err != nil { | ||
| return | ||
| } | ||
| if query.Response || query.Opcode != dns.OpcodeQuery || len(query.Question) != 1 { | ||
| return | ||
| } | ||
| response.SetReply(query) | ||
|
|
||
| // Get the RRs if possible | ||
| var ( | ||
| q0 = query.Question[0] | ||
| name = dns.CanonicalName(q0.Name) | ||
| ) | ||
| switch { | ||
| case q0.Qclass != dns.ClassINET: | ||
| response.Rcode = dns.RcodeRefused | ||
| case q0.Qtype == dns.TypeA || | ||
| q0.Qtype == dns.TypeAAAA || | ||
| q0.Qtype == dns.TypeCNAME: | ||
| var found bool | ||
| response.Answer, found = dd.lookup(q0.Qtype, name) | ||
| if !found { | ||
| response.Rcode = dns.RcodeNameError | ||
| } | ||
| default: | ||
| response.Rcode = dns.RcodeNameError | ||
| } | ||
|
|
||
| // Write the response | ||
| rawResp, err := response.Pack() | ||
| if err != nil { | ||
| return | ||
| } | ||
| rw.Write(rawResp) | ||
| } | ||
|
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||
| // lookup returns the DNS records for a domain name. | ||
| // | ||
| // This method is goroutine safe as long as one does not | ||
| // modify the database while handling queries. | ||
| func (dd *Database) lookup(qtype uint16, name string) ([]dns.RR, bool) { | ||
| const maxloops = 10 | ||
| var rrs []dns.RR | ||
| for idx := 0; idx < maxloops; idx++ { | ||
|
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| // Search whether the current name is in the database. | ||
| var interim []dns.RR | ||
| interim, found := dd.names[name] | ||
| if !found { | ||
| return nil, false | ||
| } | ||
|
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| // We have definitely found something related. | ||
| rrs = append(rrs, interim...) | ||
|
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| // Check whether we have found the desired record. | ||
| for _, rr := range interim { | ||
| if qtype == rr.Header().Rrtype { | ||
| return rrs, true | ||
| } | ||
| } | ||
|
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| // Otherwise, follow CNAME redirects. | ||
| var cname string | ||
| for _, rr := range interim { | ||
| if rr, ok := rr.(*dns.CNAME); ok { | ||
| cname = rr.Target | ||
| break | ||
| } | ||
| } | ||
| if cname == "" { | ||
| return nil, false | ||
| } | ||
|
|
||
| // Continue searching from the CNAME target. | ||
| name = cname | ||
| } | ||
|
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||
| return nil, false | ||
| } |
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