make image parent check more robust

Follow up on issue #7444 and make the parent checks more robust.
We can end up with an incoherent storage when, for instance, a
build has been killed.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/libpod/image/image.go b/libpod/image/image.go
index dee2ce0ee..2d055cc44 100644
--- a/libpod/image/image.go
+++ b/libpod/image/image.go
@@ -1247,11 +1247,14 @@ func areParentAndChild(parent, child *imgspecv1.Image) bool {
 	// candidate parent's diff IDs, which together would have
 	// controlled which layers were used
 
-	// issue #7444 describes a panic where the length of child.RootFS.DiffIDs
-	// is checked but child is nil.  Adding a simple band-aid approach to prevent
-	// the problem until the origin of the problem can be worked out in the issue
-	// itself.
-	if child == nil || len(parent.RootFS.DiffIDs) > len(child.RootFS.DiffIDs) {
+	// Both, child and parent, may be nil when the storage is left in an
+	// incoherent state.  Issue #7444 describes such a case when a build
+	// has been killed.
+	if child == nil || parent == nil {
+		return false
+	}
+
+	if len(parent.RootFS.DiffIDs) > len(child.RootFS.DiffIDs) {
 		return false
 	}
 	childUsesCandidateDiffs := true