diff options
Diffstat (limited to 'net/dns/resolver/forwarder.go')
| -rw-r--r-- | net/dns/resolver/forwarder.go | 46 |
1 files changed, 7 insertions, 39 deletions
diff --git a/net/dns/resolver/forwarder.go b/net/dns/resolver/forwarder.go index 5d1904468..68b84b557 100644 --- a/net/dns/resolver/forwarder.go +++ b/net/dns/resolver/forwarder.go @@ -10,7 +10,6 @@ import ( "encoding/binary" "errors" "fmt" - "hash/crc32" "io" "io/ioutil" "math/rand" @@ -65,44 +64,13 @@ func getTxID(packet []byte) txid { } dnsid := binary.BigEndian.Uint16(packet[0:2]) - qcount := binary.BigEndian.Uint16(packet[4:6]) - if qcount == 0 { - return txid(dnsid) - } - - offset := headerBytes - for i := uint16(0); i < qcount; i++ { - // Note: this relies on the fact that names are not compressed in questions, - // so they are guaranteed to end with a NUL byte. - // - // Justification: - // RFC 1035 doesn't seem to explicitly prohibit compressing names in questions, - // but this is exceedingly unlikely to be done in practice. A DNS request - // with multiple questions is ill-defined (which questions do the header flags apply to?) - // and a single question would have to contain a pointer to an *answer*, - // which would be excessively smart, pointless (an answer can just as well refer to the question) - // and perhaps even prohibited: a draft RFC (draft-ietf-dnsind-local-compression-05) states: - // - // > It is important that these pointers always point backwards. - // - // This is said in summarizing RFC 1035, although that phrase does not appear in the original RFC. - // Additionally, (https://cr.yp.to/djbdns/notes.html) states: - // - // > The precise rule is that a name can be compressed if it is a response owner name, - // > the name in NS data, the name in CNAME data, the name in PTR data, the name in MX data, - // > or one of the names in SOA data. - namebytes := bytes.IndexByte(packet[offset:], 0) - // ... | name | NUL | type | class - // ?? 1 2 2 - offset = offset + namebytes + 5 - if len(packet) < offset { - // Corrupt packet; don't crash. - return txid(dnsid) - } - } - - hash := crc32.ChecksumIEEE(packet[headerBytes:offset]) - return (txid(hash) << 32) | txid(dnsid) + // Previously, we hashed the question and combined it with the original txid + // which was useful when concurrent queries were multiplexed on a single + // local source port. We encountered some situations where the DNS server + // canonicalizes the question in the response (uppercase converted to + // lowercase in this case), which resulted in responses that we couldn't + // match to the original request due to hash mismatches. + return txid(dnsid) } // clampEDNSSize attempts to limit the maximum EDNS response size. This is not |