crypto/tls: return better error message in the case of an SSLv2 handshake.

Update #3930
Return a better error message in this situation.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6474055

diff --git a/src/pkg/crypto/tls/conn.go b/src/pkg/crypto/tls/conn.go
index 2a5115dc6aba08975723379632dd4a9b77180ce5..455910af41503575b69aa7aaca266fe763efe5e0 100644 (file)
--- a/src/pkg/crypto/tls/conn.go
+++ b/src/pkg/crypto/tls/conn.go
@@ -487,6 +487,16 @@ Again:
                return err
        }
        typ := recordType(b.data[0])
+
+       // No valid TLS record has a type of 0x80, however SSLv2 handshakes
+       // start with a uint16 length where the MSB is set and the first record
+       // is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
+       // an SSLv2 client.
+       if want == recordTypeHandshake && typ == 0x80 {
+               c.sendAlert(alertProtocolVersion)
+               return errors.New("tls: unsupported SSLv2 handshake received")
+       }
+
        vers := uint16(b.data[1])<<8 | uint16(b.data[2])
        n := int(b.data[3])<<8 | int(b.data[4])
        if c.haveVers && vers != c.vers {