Compute checksum when reading packfiles

1 files changed, 17 insertions, 0 deletions

diff --git a/pack_idx.go b/pack_idx.go
index 03397286..3cb89701 100644
--- a/pack_idx.go
+++ b/pack_idx.go
@@ -196,6 +196,23 @@ func (pi *packIndex) parse(buf []byte) error {
 	pi.numObjects = nobj
 	pi.names = buf[namesStart:namesEnd]
 	pi.crcs = buf[crcStart:crcEnd]
+
+	if len(buf) < 2*pi.repo.hashSize {
+		return ErrInvalidObject
+	}
+	idxChecksumStart := len(buf) - pi.repo.hashSize
+	idxChecksumInFile := buf[idxChecksumStart:]
+
+	hashFn, ok := hashFuncs[pi.repo.hashSize]
+	if !ok {
+		return fmt.Errorf("furgit: unsupported hash size %d", pi.repo.hashSize)
+	}
+
+	computedHash := hashFn(buf[:idxChecksumStart])
+	if !bytes.Equal(computedHash.data[:pi.repo.hashSize], idxChecksumInFile) {
+		return fmt.Errorf("furgit: index checksum mismatch in %s", pi.idxRel)
+	}
+
 	return nil
 }