From c94b797f000333256058b08aeb573d45055a9b99 Mon Sep 17 00:00:00 2001
From: Simon Frei <freisim93@gmail.com>
Date: Wed, 6 Oct 2021 10:26:54 +0200
Subject: [PATCH] lib/protocol: Preserve sequence decrypting fileinfos (fixes
 #7994) (#7995)

---
 lib/protocol/encryption.go      |  4 ++++
 lib/protocol/encryption_test.go | 11 +++++++++++
 2 files changed, 15 insertions(+)

diff --git a/lib/protocol/encryption.go b/lib/protocol/encryption.go
index 540c3c8f9..b6e747b70 100644
--- a/lib/protocol/encryption.go
+++ b/lib/protocol/encryption.go
@@ -365,6 +365,10 @@ func DecryptFileInfo(fi FileInfo, folderKey *[keySize]byte) (FileInfo, error) {
 	if err := proto.Unmarshal(dec, &decFI); err != nil {
 		return FileInfo{}, err
 	}
+
+	// Preserve sequence, which is legitimately controlled by the untrusted device
+	decFI.Sequence = fi.Sequence
+
 	return decFI, nil
 }
 
diff --git a/lib/protocol/encryption_test.go b/lib/protocol/encryption_test.go
index d0ae23e33..74fef448a 100644
--- a/lib/protocol/encryption_test.go
+++ b/lib/protocol/encryption_test.go
@@ -139,6 +139,7 @@ func encFileInfo() FileInfo {
 		Size:        45,
 		Permissions: 0755,
 		ModifiedS:   8080,
+		Sequence:    1000,
 		Blocks: []BlockInfo{
 			{
 				Offset: 0,
@@ -165,6 +166,9 @@ func TestEnDecryptFileInfo(t *testing.T) {
 	if enc.RawBlockSize < MinBlockSize {
 		t.Error("Too small raw block size:", enc.RawBlockSize)
 	}
+	if enc.Sequence != fi.Sequence {
+		t.Error("encrypted fileinfo didn't maintain sequence number")
+	}
 	again := encryptFileInfo(fi, &key)
 	if !bytes.Equal(enc.Blocks[0].Hash, again.Blocks[0].Hash) {
 		t.Error("block hashes should remain stable (0)")
@@ -173,10 +177,17 @@ func TestEnDecryptFileInfo(t *testing.T) {
 		t.Error("block hashes should remain stable (1)")
 	}
 
+	// Simulate the remote setting the sequence number when writing to db
+	enc.Sequence = 10
+
 	dec, err := DecryptFileInfo(enc, &key)
 	if err != nil {
 		t.Error(err)
 	}
+	if dec.Sequence != enc.Sequence {
+		t.Error("decrypted fileinfo didn't maintain sequence number")
+	}
+	dec.Sequence = fi.Sequence
 	if !reflect.DeepEqual(fi, dec) {
 		t.Error("mismatch after decryption")
 	}