Added packLen
packLen() returns the length of an uncompressed packet buffer, this is used when packing a packet. This is needed for compression. When compression is used, we first create the full packet and *then* compress it. If we use Len() which accounts for compression, we can get buffer overruns, when packing the (then still uncompressed) packet.
This commit is contained in:
Miek Gieben
parent
d83e816f30
commit
1ad76fe65b
57
dns_test.go
57
dns_test.go
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@ -159,49 +159,34 @@ func TestCompressLength(t *testing.T) {
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// Does the predicted length match final packed length
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func TestMsgLenTest(t *testing.T) {
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var (
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// util function to build messages
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makeMsg = func(question string, ans, ns, e []RR) *Msg {
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var msg Msg
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msg.SetQuestion(Fqdn(question), TypeANY)
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msg.Answer = append(msg.Answer, ans...)
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msg.Ns = append(msg.Ns, ns...)
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msg.Extra = append(msg.Extra, e...)
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msg.Compress = true
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return &msg
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}
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// util function to build messages
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makeMsg := func(question string, ans, ns, e []RR) *Msg {
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msg := new(Msg)
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msg.SetQuestion(Fqdn(question), TypeANY)
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msg.Answer = append(msg.Answer, ans...)
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msg.Ns = append(msg.Ns, ns...)
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msg.Extra = append(msg.Extra, e...)
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msg.Compress = true
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return msg
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}
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name = "12345678901234567890123456789012345.12345678.123."
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rrA, _ = NewRR(name + " 3600 IN A 192.0.2.1")
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rrMx, _ = NewRR(name + " 3600 IN MX 10 " + name)
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rrTxt, _ = NewRR(name + ` 3600 IN TXT "I am a TXT"`)
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tests = []*Msg{
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makeMsg(name, nil, nil, nil),
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makeMsg(name, []RR{rrA}, nil, nil),
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makeMsg(name, []RR{rrMx}, nil, nil),
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makeMsg(name, []RR{rrTxt}, nil, nil),
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makeMsg(name, []RR{rrA, rrA}, nil, nil),
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makeMsg(name, []RR{rrMx, rrMx}, nil, nil),
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makeMsg(name, []RR{rrTxt, rrTxt}, nil, nil),
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makeMsg(name, []RR{rrA}, []RR{rrA}, nil),
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makeMsg(name, []RR{rrMx}, []RR{rrMx}, nil),
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makeMsg(name, []RR{rrTxt}, []RR{rrTxt}, nil),
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makeMsg(name, []RR{rrA, rrMx, rrTxt}, []RR{rrA, rrMx, rrTxt}, nil),
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makeMsg(name, []RR{rrA, rrMx, rrTxt}, []RR{rrA, rrMx, rrTxt}, []RR{rrA, rrMx, rrTxt})}
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)
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name1 := "12345678901234567890123456789012345.12345678.123."
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rrA, _ := NewRR(name1 + " 3600 IN A 192.0.2.1")
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rrMx, _ := NewRR(name1 + " 3600 IN MX 10 " + name1)
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tests := []*Msg{
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makeMsg(name1, []RR{rrA}, nil, nil),
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makeMsg(name1, []RR{rrMx, rrMx}, nil, nil)}
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for _, msg := range tests {
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var (
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predicted = msg.Len()
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buf, err = msg.Pack()
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actual = len(buf)
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)
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predicted := msg.Len()
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buf, err := msg.Pack()
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if err != nil {
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t.Error(err)
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t.Fail()
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}
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if predicted != actual {
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t.Errorf("Predicted length is wrong: predicted %d, actual %d\n%s", predicted, actual, msg)
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if predicted != len(buf) {
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t.Errorf("Predicted length is wrong: predicted %s (len=%d) %d, actual %d\n",
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msg.Question[0].Name, len(msg.Answer), predicted, len(buf))
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t.Fail()
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}
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}
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44
msg.go
44
msg.go
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@ -283,7 +283,7 @@ func PackDomainName(s string, msg []byte, off int, compression map[string]int, c
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// the offset of the current name, because that's
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// where we need to insert the pointer later
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// If compress is true, we're allowed to compress this dname
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// If compress is true, we're allowed to compress this dname
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if pointer == -1 && compress {
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pointer = p // Where to point to
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nameoffset = offset // Where to point from
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@ -298,7 +298,7 @@ func PackDomainName(s string, msg []byte, off int, compression map[string]int, c
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if len(bs) == 1 && bs[0] == '.' {
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return off, nil
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}
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// If we did compression and we find something at the pointer here
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// If we did compression and we find something add the pointer here
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if pointer != -1 {
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// We have two bytes (14 bits) to put the pointer in
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msg[nameoffset], msg[nameoffset+1] = packUint16(uint16(pointer ^ 0xC000))
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@ -1255,9 +1255,7 @@ func (dns *Msg) Pack() (msg []byte, err error) {
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dh.Nscount = uint16(len(ns))
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dh.Arcount = uint16(len(extra))
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// TODO(mg): still a little too much, but better than 64K...
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msg = make([]byte, dns.Len()+10)
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msg = make([]byte, dns.packLen()+10) // TODO(miekg): +10 should go sometimses
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// Pack it in: header and then the pieces.
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off := 0
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off, err = packStructCompress(&dh, msg, off, compression, dns.Compress)
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@ -1393,10 +1391,28 @@ func (dns *Msg) String() string {
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return s
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}
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// Len return the message length when in (un)compressed wire format.
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// packLen returns the message length when in UNcompressed wire format.
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func (dns *Msg) packLen() int {
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// Message header is always 12 bytes
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l := 12
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for i := 0; i < len(dns.Question); i++ {
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l += dns.Question[i].len()
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}
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for i := 0; i < len(dns.Answer); i++ {
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l += dns.Answer[i].len()
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}
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for i := 0; i < len(dns.Ns); i++ {
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l += dns.Ns[i].len()
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}
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for i := 0; i < len(dns.Extra); i++ {
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l += dns.Extra[i].len()
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}
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return l
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}
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// Len returns the message length when in (un)compressed wire format.
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// If dns.Compress is true compression it is taken into account, currently
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// this only counts owner name compression. There is no check for
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// nil valued sections (allocated, but contain no RRs).
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// this only counts owner name compression.
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func (dns *Msg) Len() int {
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// Message header is always 12 bytes
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l := 12
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@ -1413,8 +1429,8 @@ func (dns *Msg) Len() int {
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}
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for i := 0; i < len(dns.Answer); i++ {
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if dns.Compress {
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if v, ok := compression[dns.Answer[i].Header().Name]; ok {
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l += dns.Answer[i].len() - v
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if _, ok := compression[dns.Answer[i].Header().Name]; ok {
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l += dns.Answer[i].len() - len(dns.Answer[i].Header().Name) + 2
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continue
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}
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compressionHelper(compression, dns.Answer[i].Header().Name)
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@ -1423,8 +1439,8 @@ func (dns *Msg) Len() int {
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}
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for i := 0; i < len(dns.Ns); i++ {
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if dns.Compress {
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if v, ok := compression[dns.Ns[i].Header().Name]; ok {
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l += dns.Ns[i].len() - v
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if _, ok := compression[dns.Ns[i].Header().Name]; ok {
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l += dns.Ns[i].len() - len(dns.Ns[i].Header().Name) + 2
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continue
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}
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compressionHelper(compression, dns.Ns[i].Header().Name)
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@ -1433,8 +1449,8 @@ func (dns *Msg) Len() int {
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}
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for i := 0; i < len(dns.Extra); i++ {
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if dns.Compress {
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if v, ok := compression[dns.Extra[i].Header().Name]; ok {
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l += dns.Extra[i].len() - v
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if _, ok := compression[dns.Extra[i].Header().Name]; ok {
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l += dns.Extra[i].len() - len(dns.Extra[i].Header().Name) + 2
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continue
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}
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compressionHelper(compression, dns.Extra[i].Header().Name)
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