sysenc: refuse to unmarshal into undersized dst

Unmarshal currently doesn't check that unmarshaling actually
consumes to full buffer. This means that looking uint16 from an
uint32 value doesn't return an error.

Fixes #1157

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

internal/sysenc/marshal.go

@@ -99,7 +99,15 @@ func Unmarshal(data interface{}, buf []byte) error {
 
 		rd.Reset(buf)
 
-		return binary.Read(rd, internal.NativeEndian, value)
+		if err := binary.Read(rd, internal.NativeEndian, value); err != nil {
+			return err
+		}
+
+		if rd.Len() != 0 {
+			return fmt.Errorf("unmarshaling %T doesn't consume all data", data)
+		}
+
+		return nil
 	}
 }
 

map_test.go

@@ -227,6 +227,14 @@ func TestBatchAPIHash(t *testing.T) {
 	}
 }
 
+func TestMapLookupKeyTooSmall(t *testing.T) {
+	m := createArray(t)
+
+	var small uint16
+	qt.Assert(t, m.Put(uint32(0), uint32(1234)), qt.IsNil)
+	qt.Assert(t, m.Lookup(uint32(0), &small), qt.IsNotNil)
+}
+
 func TestBatchAPIMapDelete(t *testing.T) {
 	if err := haveBatchAPI(); err != nil {
 		t.Skipf("batch api not available: %v", err)