commit-graph: verify parent list

The commit-graph file stores parents in a two-column portion of the
commit data chunk. If there is only one parent, then the second column
stores 0xFFFFFFFF to indicate no second parent.

The 'verify' subcommand checks the parent list for the commit loaded
from the commit-graph and the one parsed from the object database. Test
these checks for corrupt parents, too many parents, and wrong parents.

Add a boundary check to insert_parent_or_die() for when the parent
position value is out of range.

The octopus merge will be tested in a later commit.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/commit-graph.c b/commit-graph.c
index 17624b90d7..a79b06f37a 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -244,6 +244,9 @@ static struct commit_list **insert_parent_or_die(struct commit_graph *g,
 	struct commit *c;
 	struct object_id oid;
 
+	if (pos >= g->num_commits)
+		die("invalid parent position %"PRIu64, pos);
+
 	hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
 	c = lookup_commit(&oid);
 	if (!c)
@@ -907,6 +910,7 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g)
 
 	for (i = 0; i < g->num_commits; i++) {
 		struct commit *graph_commit, *odb_commit;
+		struct commit_list *graph_parents, *odb_parents;
 
 		hashcpy(cur_oid.hash, g->chunk_oid_lookup + g->hash_len * i);
 
@@ -924,6 +928,30 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g)
 				     oid_to_hex(&cur_oid),
 				     oid_to_hex(get_commit_tree_oid(graph_commit)),
 				     oid_to_hex(get_commit_tree_oid(odb_commit)));
+
+		graph_parents = graph_commit->parents;
+		odb_parents = odb_commit->parents;
+
+		while (graph_parents) {
+			if (odb_parents == NULL) {
+				graph_report("commit-graph parent list for commit %s is too long",
+					     oid_to_hex(&cur_oid));
+				break;
+			}
+
+			if (oidcmp(&graph_parents->item->object.oid, &odb_parents->item->object.oid))
+				graph_report("commit-graph parent for %s is %s != %s",
+					     oid_to_hex(&cur_oid),
+					     oid_to_hex(&graph_parents->item->object.oid),
+					     oid_to_hex(&odb_parents->item->object.oid));
+
+			graph_parents = graph_parents->next;
+			odb_parents = odb_parents->next;
+		}
+
+		if (odb_parents != NULL)
+			graph_report("commit-graph parent list for commit %s terminates early",
+				     oid_to_hex(&cur_oid));
 	}
 
 	return verify_commit_graph_error;