static ssize_t ucma_process_join(struct ucma_file *file,
				 struct rdma_ucm_join_mcast *cmd,  int out_len)
{
	struct rdma_ucm_create_id_resp resp;
	struct ucma_context *ctx;
	struct ucma_multicast *mc;
	struct sockaddr *addr;
	int ret;
	u8 join_state;

	if (out_len < sizeof(resp))
		return -ENOSPC;

	addr = (struct sockaddr *) &cmd->addr;
	if (cmd->addr_size != rdma_addr_size(addr))
		return -EINVAL;

	if (cmd->join_flags == RDMA_MC_JOIN_FLAG_FULLMEMBER)
		join_state = BIT(FULLMEMBER_JOIN);
	else if (cmd->join_flags == RDMA_MC_JOIN_FLAG_SENDONLY_FULLMEMBER)
		join_state = BIT(SENDONLY_FULLMEMBER_JOIN);
	else
		return -EINVAL;

	ctx = ucma_get_ctx_dev(file, cmd->id);
	if (IS_ERR(ctx))
		return PTR_ERR(ctx);

	mutex_lock(&file->mut);
	mc = ucma_alloc_multicast(ctx);
	if (!mc) {
		ret = -ENOMEM;
		goto err1;
	}
	mc->join_state = join_state;
	mc->uid = cmd->uid;
	memcpy(&mc->addr, addr, cmd->addr_size);
	ret = rdma_join_multicast(ctx->cm_id, (struct sockaddr *)&mc->addr,
				  join_state, mc);
	if (ret)
		goto err2;

	resp.id = mc->id;
	if (copy_to_user(u64_to_user_ptr(cmd->response),
			 &resp, sizeof(resp))) {
		ret = -EFAULT;
 		goto err3;
 	}
 
 	mutex_unlock(&file->mut);
 	ucma_put_ctx(ctx);
 	return 0;

err3:
	rdma_leave_multicast(ctx->cm_id, (struct sockaddr *) &mc->addr);
	ucma_cleanup_mc_events(mc);
err2:
	mutex_lock(&mut);
	idr_remove(&multicast_idr, mc->id);
	mutex_unlock(&mut);
	list_del(&mc->list);
	kfree(mc);
err1:
	mutex_unlock(&file->mut);
	ucma_put_ctx(ctx);
	return ret;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.