Parse TCG_PCClientPCREvent structures with an eventSize of 0 (#212)

Author: brandonweeks

attest/eventlog.go

@@ -657,9 +657,6 @@ func parseRawEvent(r *bytes.Buffer, specID *specIDEvent) (event rawEvent, err er
 	if err = binary.Read(r, binary.LittleEndian, &h); err != nil {
 		return event, fmt.Errorf("header deserialization error: %w", err)
 	}
-	if h.EventSize == 0 {
-		return event, errors.New("event data size is 0")
-	}
 	if h.EventSize > uint32(r.Len()) {
 		return event, &eventSizeErr{h.EventSize, r.Len()}
 	}

attest/eventlog_test.go

@@ -15,6 +15,7 @@
 package attest
 
 import (
+	"bytes"
 	"encoding/json"
 	"io/ioutil"
 	"testing"
@@ -149,6 +150,29 @@ func TestParseEventLogEventSizeTooLarge(t *testing.T) {
 	}
 }
 
+func TestParseEventLogEventSizeZero(t *testing.T) {
+	data := []byte{
+		// PCR index
+		0x4, 0x0, 0x0, 0x0,
+
+		// type
+		0xd, 0x0, 0x0, 0x0,
+
+		// Digest
+		0x94, 0x2d, 0xb7, 0x4a, 0xa7, 0x37, 0x5b, 0x23, 0xea, 0x23,
+		0x58, 0xeb, 0x3b, 0x31, 0x59, 0x88, 0x60, 0xf6, 0x90, 0x59,
+
+		// Event size (0 B)
+		0x0, 0x0, 0x0, 0x0,
+
+		// no "event data"
+	}
+
+	if _, err := parseRawEvent(bytes.NewBuffer(data), nil); err != nil {
+		t.Fatalf("parsing event log: %v", err)
+	}
+}
+
 func TestParseShortNoAction(t *testing.T) {
 	// https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClientSpecPlat_TPM_2p0_1p04_pub.pdf#page=110
 	// says: "For EV_NO_ACTION events other than the EFI Specification ID event