void __cleanup_sighand(struct sighand_struct *sighand)
{
	if (atomic_dec_and_test(&sighand->count)) {
		signalfd_cleanup(sighand);
		/*
		 * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
		 * without an RCU grace period, see __lock_task_sighand().
		 */
		kmem_cache_free(sighand_cachep, sighand);
	}
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.