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BFD: check lengths when decoding auth header #887

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16 changes: 11 additions & 5 deletions layers/bfd.go
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Original file line number Diff line number Diff line change
Expand Up @@ -374,6 +374,10 @@ func (d *BFD) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
data, d.RequiredMinEchoRxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))

if d.AuthPresent && (len(data) > 2) {
authLen := uint8(data[1])
if len(data) != int(authLen) {
return errors.New("BFD Authentication Header length does not match")
}
d.AuthHeader = &BFDAuthHeader{}
data, d.AuthHeader.AuthType = data[1:], BFDAuthType(data[0])
data, _ = data[1:], uint8(data[0]) // Consume length
Expand All @@ -382,11 +386,13 @@ func (d *BFD) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
switch d.AuthHeader.AuthType {
case BFDAuthTypePassword:
d.AuthHeader.Data = BFDAuthData(data)
case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5:
// Skipped reserved byte
data, d.AuthHeader.SequenceNumber = data[5:], BFDAuthSequenceNumber(binary.BigEndian.Uint32(data[1:5]))
d.AuthHeader.Data = BFDAuthData(data)
case BFDAuthTypeKeyedSHA1, BFDAuthTypeMeticulousKeyedSHA1:
case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5,
BFDAuthTypeKeyedSHA1, BFDAuthTypeMeticulousKeyedSHA1:

if len(data) < 5 { // 1 byte reserved + 4 byte sequence number
df.SetTruncated()
return errors.New("BFD Authentication Header too short")
}
// Skipped reserved byte
data, d.AuthHeader.SequenceNumber = data[5:], BFDAuthSequenceNumber(binary.BigEndian.Uint32(data[1:5]))
d.AuthHeader.Data = BFDAuthData(data)
Expand Down
22 changes: 21 additions & 1 deletion layers/bfd_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,11 @@
package layers

import (
"github.com/google/gopacket"
"reflect"
"strings"
"testing"

"github.com/google/gopacket"
)

//******************************************************************************
Expand Down Expand Up @@ -287,3 +289,21 @@ func TestBFDAuthTypeMeticulousKeyedSHA1(t *testing.T) {

checkBFD("TestBFDAuthTypeMeticulousKeyedSHA1", t, testPacketBFD, pExpectedBFD)
}

func TestBFDAuthTypeKeyedMD5Truncated(t *testing.T) {

// testPacketBFDTrunc is the packet from TestBFDAuthTypeKeyedMD5 with the
// Auth Header truncated to 7 bytes (i.e. cut off the last byte of the
// Sequence Number field) and length fields adapted; stripped lower layers.
var testPacketBFDTrunc = []byte{
0x20, 0x44, 0x05, 0x1f, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
0x00, 0x0f, 0x42, 0x40, 0x00, 0x0f, 0x42, 0x40, 0x00, 0x00, 0x00, 0x00,
0x02, 0x07, 0x02, 0x00, 0x00, 0x00, 0x00,
}
p := gopacket.NewPacket(testPacketBFDTrunc, LayerTypeBFD, gopacket.Default)
if errLayer := p.ErrorLayer(); errLayer == nil {
t.Error("No error layer on invalid BFD Authentication Header")
} else if err := errLayer.Error(); !strings.Contains(err.Error(), "BFD Authentication Header too short") {
t.Errorf("unexpected error message: %v", err)
}
}