receive-pack: check object type of sha1 before using them as commits

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/receive-pack.c b/receive-pack.c
index fba4cf82353ff43eae7430c863680f481e03dcb0..d0a563df6457a6fc5b40b3502582a78fafdadd53 100644 (file)
--- a/receive-pack.c
+++ b/receive-pack.c
@@ -178,11 +178,21 @@ static const char *update(struct command *cmd)
        if (deny_non_fast_forwards && !is_null_sha1(new_sha1) &&
            !is_null_sha1(old_sha1) &&
            !prefixcmp(name, "refs/heads/")) {
+               struct object *old_object, *new_object;
                struct commit *old_commit, *new_commit;
                struct commit_list *bases, *ent;
 
-               old_commit = (struct commit *)parse_object(old_sha1);
-               new_commit = (struct commit *)parse_object(new_sha1);
+               old_object = parse_object(old_sha1);
+               new_object = parse_object(new_sha1);
+
+               if (!old_object || !new_object ||
+                   old_object->type != OBJ_COMMIT ||
+                   new_object->type != OBJ_COMMIT) {
+                       error("bad sha1 objects for %s", name);
+                       return "bad ref";
+               }
+               old_commit = (struct commit *)old_object;
+               new_commit = (struct commit *)new_object;
                bases = get_merge_bases(old_commit, new_commit, 1);
                for (ent = bases; ent; ent = ent->next)
                        if (!hashcmp(old_sha1, ent->item->object.sha1))