x/net/dns/dnsmessage: does not support RFC 2673 bit-string labels

[chushuai]

What version of Go are you using (go version)?

$ go version  
go version go1.18.1 linux/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.18.1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2993232734=/tmp/go-build -gno-record-gcc-switches"

What did you do?

` Here is TCP DNS payload hexStream := "00600006850000010001000100000776657273696f6e0462696e640000100003c00c0010000300000000002827392e382e327263312d5265644861742d392e382e322d302e36382e7263312e656c365f31302e38c00c00020003000000000002c00c"

data, _ := hex.DecodeString(hexStream)`

https://github.com/golang/net/blob/1d1ef9303861d099ec7e69ccb17377e0c443542d/dns/dnsmessage/message.go#L2041

• wireshark code here

  case 0x40:
  //Extended label (RFC 2673) 
  switch (component_len & 0x3f) {
  
    case 0x01:
      /* Bitstring label */
    {
      int bit_count;
      int label_len;
      int print_len;
  
      bit_count = tvb_get_guint8(tvb, offset);
      offset++;
      label_len = (bit_count - 1) / 8 + 1;
  
      if (maxname > 0) {
        print_len = g_snprintf(np, maxname, "\\[x");
        if (print_len <= maxname) {
          np      += print_len;
          maxname -= print_len;
        } else {
          /* Nothing printed, as there's no room.
             Suppress all subsequent printing. */
          maxname = 0;
        }
      }
      while (label_len--) {
        if (maxname > 0) {
          print_len = g_snprintf(np, maxname, "%02x",
                                 tvb_get_guint8(tvb, offset));
          if (print_len <= maxname) {
            np      += print_len;
            maxname -= print_len;
          } else {
            /* Nothing printed, as there's no room.
               Suppress all subsequent printing. */
            maxname = 0;
          }
        }
        offset++;
      }
      if (maxname > 0) {
        print_len = g_snprintf(np, maxname, "/%d]", bit_count);
        if (print_len <= maxname) {
          np      += print_len;
          maxname -= print_len;
        } else {
          /* Nothing printed, as there's no room.
             Suppress all subsequent printing. */
          maxname = 0;
        }
      }
    }
    break;
  
    default:
      *name="<Unknown extended label>";
      *name_len = (guint)strlen(*name);
      /* Parsing will probably fail from here on, since the */
      /* label length is unknown... */
      len = offset - start_offset;
      if (len < min_len) {
        THROW(ReportedBoundsError);
      }
      return len;
  }
  break;`

What did you expect to see?

What did you see instead?

[mateusz834]

As a note the Bit-String Labels are deprecated by RFC 6891.

[RFC2671] specified extended label types. The only such label proposed was in [RFC2673] for a label type called "Bit-String Label" or "Binary Labels", with this latest term being the one in common use. For various reasons, introducing a new label type was found to be extremely difficult, and [RFC2673] was moved to Experimental. This document obsoletes [RFC2673], deprecating Binary Labels. Extended labels remain defined, but their use is discouraged due to practical difficulties with deployment; their use in the future SHOULD only be considered after careful evaluation of the deployment hindrances.