From 1a0fcb5c97ce5d7cc9dac1e6fa82065dd7f8ddc8 Mon Sep 17 00:00:00 2001
From: Kent <kent.rancourt@gmail.com>
Date: Fri, 22 Sep 2023 16:41:04 -0400
Subject: [PATCH] return error if it looks like a branch hijacking

Signed-off-by: Kent <kent.rancourt@gmail.com>
---
 service.go | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/service.go b/service.go
index c7cf351..84e1e02 100644
--- a/service.go
+++ b/service.go
@@ -157,6 +157,13 @@ func (s *service) RenderManifests(
 	if err != nil {
 		return res, errors.Wrap(err, "error loading branch metadata")
 	}
+	if oldTargetBranchMetadata == nil {
+		return res, errors.Errorf(
+			"target branch %q already exists, but does not appear to be managed by "+
+				"Bookkeeper; refusing to overwrite branch contents",
+			rc.request.TargetBranch,
+		)
+	}
 	rc.target.oldBranchMetadata = *oldTargetBranchMetadata
 
 	if rc.target.commit.branch, err = switchToCommitBranch(rc); err != nil {