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crypto/tls: reject CT extension with no SCTs included

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When the CT extension is enabled but no SCTs are present, the existing
code calls "continue" which causes resizing the data byte slice to be
skipped. In fact, such extensions should be rejected.

Fixes #17958

Change-Id: Iad12da10d1ea72d04ae2e1012c28bb2636f06bcd
Reviewed-on: https://go-review.googlesource.com/33265
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
woodsaj 2016-11-17 20:14:32 +08:00 committed by Brad Fitzpatrick
parent 85c867c672
commit 8b63f202ce
2 changed files with 46 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
handshake_messages.go
View File

@ -802,12 +802,9 @@ func (m *serverHelloMsg) unmarshal(data []byte) bool {
} }
l := int(d[0])<<8 | int(d[1]) l := int(d[0])<<8 | int(d[1])
d = d[2:] d = d[2:]
if len(d) != l { if len(d) != l || l == 0 {
return false return false
} }
if l == 0 {
continue
}
m.scts = make([][]byte, 0, 3) m.scts = make([][]byte, 0, 3)
for len(d) != 0 { for len(d) != 0 {

45
handshake_messages_test.go
View File

@ -5,6 +5,7 @@
package tls package tls
import ( import (
"bytes"
"math/rand" "math/rand"
"reflect" "reflect"
"testing" "testing"
@ -260,3 +261,47 @@ func (*sessionState) Generate(rand *rand.Rand, size int) reflect.Value {
} }
return reflect.ValueOf(s) return reflect.ValueOf(s)
} }
func TestRejectEmptySCTList(t *testing.T) {
// https://tools.ietf.org/html/rfc6962#section-3.3.1 specifies that
// empty SCT lists are invalid.
var random [32]byte
sct := []byte{0x42, 0x42, 0x42, 0x42}
serverHello := serverHelloMsg{
vers: VersionTLS12,
random: random[:],
scts: [][]byte{sct},
}
serverHelloBytes := serverHello.marshal()
var serverHelloCopy serverHelloMsg
if !serverHelloCopy.unmarshal(serverHelloBytes) {
t.Fatal("Failed to unmarshal initial message")
}
// Change serverHelloBytes so that the SCT list is empty
i := bytes.Index(serverHelloBytes, sct)
if i < 0 {
t.Fatal("Cannot find SCT in ServerHello")
}
var serverHelloEmptySCT []byte
serverHelloEmptySCT = append(serverHelloEmptySCT, serverHelloBytes[:i-6]...)
// Append the extension length and SCT list length for an empty list.
serverHelloEmptySCT = append(serverHelloEmptySCT, []byte{0, 2, 0, 0}...)
serverHelloEmptySCT = append(serverHelloEmptySCT, serverHelloBytes[i+4:]...)
// Update the handshake message length.
serverHelloEmptySCT[1] = byte((len(serverHelloEmptySCT) - 4) >> 16)
serverHelloEmptySCT[2] = byte((len(serverHelloEmptySCT) - 4) >> 8)
serverHelloEmptySCT[3] = byte(len(serverHelloEmptySCT) - 4)
// Update the extensions length
serverHelloEmptySCT[42] = byte((len(serverHelloEmptySCT) - 44) >> 8)
serverHelloEmptySCT[43] = byte((len(serverHelloEmptySCT) - 44))
if serverHelloCopy.unmarshal(serverHelloEmptySCT) {
t.Fatal("Unmarshaled ServerHello with empty SCT list")
}
}