input validation in receive-pack

[mkoegler@auto.tuwien.ac.at (Martin Koegler)]

In the function "static const char *update(struct command *cmd)" in
receive-pack.c:

|        if (deny_non_fast_forwards && !is_null_sha1(new_sha1) &&
|            !is_null_sha1(old_sha1) &&
|            !prefixcmp(name, "refs/heads/")) {
|                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);
|                bases = get_merge_bases(old_commit, new_commit, 1);
|                for (ent = bases; ent; ent = ent->next)
|                        if (!hashcmp(old_sha1, ent->item->object.sha1))
|                                break;
|                free_commit_list(bases);
|                if (!ent) {
|                        error("denying non-fast forward %s"
|                              " (you should pull first)", name);
|                        return "non-fast forward";
|                }
|        }

As far as I understand the code, it assumes, that sha1 values provided
by the client really point to a commit. Shouldn't there be a check for
the object type?

Some lines above:
|        if (!prefixcmp(name, "refs/") && check_ref_format(name + 5)) {
|                error("refusing to create funny ref '%s' remotely", name);
|                return "funny refname";
|        }

Is this code really correct? All refnames starting with "refs/" may
only contain allowed characters, while all other may contain any
characters (except \0 and \n)?

For the updating code path, lock_any_ref_for_update calls
check_ref_format, so the error will happen latter. For the delete code
path, the refname seems not to be checked.

In the update code path, the check is done in refs.c:
| struct ref_lock *lock_any_ref_for_update(const char *ref, const unsigned char *old_sha1, int flags)
| {
|         if (check_ref_format(ref) == -1)
|                 return NULL;
|         return lock_ref_sha1_basic(ref, old_sha1, flags, NULL);
| }

check_ref_format may also return -2 (less than two name levels) and -3
(* at the end), which are ignored. Is it really intended, that
receive-pack can create such refs.

mfg Martin Kögler