KEYS: ensure we free the assoc array edit if edit is valid

__key_link_end is not freeing the associated array edit structure
and this leads to a 512 byte memory leak each time an identical
existing key is added with add_key().

The reason the add_key() system call returns okay is that
key_create_or_update() calls __key_link_begin() before checking to see
whether it can update a key directly rather than adding/replacing - which
it turns out it can.  Thus __key_link() is not called through
__key_instantiate_and_link() and __key_link_end() must cancel the edit.

CVE-2015-1333

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
static bool keyring_compare_object(const void *object, const void *data)
{
	const struct keyring_index_key *index_key = data;
	const struct key *key = keyring_ptr_to_key(object);

	return key->index_key.type == index_key->type &&
		key->index_key.desc_len == index_key->desc_len &&
		memcmp(key->index_key.description, index_key->description,
		       index_key->desc_len) == 0;
}

static bool keyring_compare_object(const void *object, const void *data)
{
	const struct keyring_index_key *index_key = data;
	const struct key *key = keyring_ptr_to_key(object);

	return key->index_key.type == index_key->type &&
		key->index_key.desc_len == index_key->desc_len &&
		memcmp(key->index_key.description, index_key->description,
		       index_key->desc_len) == 0;
}
