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Message-ID: <60f68f6b-5fff-6a39-b77b-4bbb86f1c87e@huawei.com>
Date: Wed, 15 Sep 2021 11:36:47 +0800
From: "yukuai (C)" <yukuai3@...wei.com>
To: Ming Lei <ming.lei@...hat.com>
CC: <axboe@...nel.dk>, <josef@...icpanda.com>, <hch@...radead.org>,
<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<nbd@...er.debian.org>, <yi.zhang@...wei.com>
Subject: Re: [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req()
On 2021/09/15 11:16, Ming Lei wrote:
> On Wed, Sep 15, 2021 at 09:54:09AM +0800, yukuai (C) wrote:
>> On 2021/09/14 22:37, Ming Lei wrote:
>>> On Tue, Sep 14, 2021 at 05:19:31PM +0800, yukuai (C) wrote:
>>>> On 在 2021/09/14 15:46, Ming Lei wrote:
>>>>
>>>>> If the above can happen, blk_mq_find_and_get_req() may not fix it too, just
>>>>> wondering why not take the following simpler way for avoiding the UAF?
>>>>>
>>>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>>>>> index 5170a630778d..dfa5cce71f66 100644
>>>>> --- a/drivers/block/nbd.c
>>>>> +++ b/drivers/block/nbd.c
>>>>> @@ -795,9 +795,13 @@ static void recv_work(struct work_struct *work)
>>>>> work);
>>>>> struct nbd_device *nbd = args->nbd;
>>>>> struct nbd_config *config = nbd->config;
>>>>> + struct request_queue *q = nbd->disk->queue;
>>>>> struct nbd_cmd *cmd;
>>>>> struct request *rq;
>>>>> + if (!percpu_ref_tryget(&q->q_usage_counter))
>>>>> + return;
>>>>> +
>>>>> while (1) {
>>>>> cmd = nbd_read_stat(nbd, args->index);
>>>>> if (IS_ERR(cmd)) {
>>>>> @@ -813,6 +817,7 @@ static void recv_work(struct work_struct *work)
>>>>> if (likely(!blk_should_fake_timeout(rq->q)))
>>>>> blk_mq_complete_request(rq);
>>>>> }
>>>>> + blk_queue_exit(q);
>>>>> nbd_config_put(nbd);
>>>>> atomic_dec(&config->recv_threads);
>>>>> wake_up(&config->recv_wq);
>>>>>
>>>>
>>>> Hi, Ming
>>>>
>>>> This apporch is wrong.
>>>>
>>>> If blk_mq_freeze_queue() is called, and nbd is waiting for all
>>>> request to complete. percpu_ref_tryget() will fail here, and deadlock
>>>> will occur because request can't complete in recv_work().
>>>
>>> No, percpu_ref_tryget() won't fail until ->q_usage_counter is zero, when
>>> it is perfectly fine to do nothing in recv_work().
>>>
>>
>> Hi Ming
>>
>> This apporch is a good idea, however we should not get q_usage_counter
>> in reccv_work(), because It will block freeze queue.
>>
>> How about get q_usage_counter in nbd_read_stat(), and put in error path
>> or after request completion?
>
> OK, looks I missed that nbd_read_stat() needs to wait for incoming reply
> first, so how about the following change by partitioning nbd_read_stat()
> into nbd_read_reply() and nbd_handle_reply()?
Hi, Ming
The change looks good to me.
Do you want to send a patch to fix this?
Thanks,
Kuai
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 5170a630778d..477fe057fc93 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -683,38 +683,47 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
> return 0;
> }
>
> -/* NULL returned = something went wrong, inform userspace */
> -static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
> +static int nbd_read_reply(struct nbd_device *nbd, int index,
> + struct nbd_reply *reply)
> {
> - struct nbd_config *config = nbd->config;
> int result;
> - struct nbd_reply reply;
> - struct nbd_cmd *cmd;
> - struct request *req = NULL;
> - u64 handle;
> - u16 hwq;
> - u32 tag;
> - struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
> + struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
> struct iov_iter to;
> - int ret = 0;
>
> - reply.magic = 0;
> + reply->magic = 0;
> iov_iter_kvec(&to, READ, &iov, 1, sizeof(reply));
> result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
> - if (result <= 0) {
> - if (!nbd_disconnected(config))
> + if (result < 0) {
> + if (!nbd_disconnected(nbd->config))
> dev_err(disk_to_dev(nbd->disk),
> "Receive control failed (result %d)\n", result);
> - return ERR_PTR(result);
> + return result;
> }
>
> - if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
> + if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
> dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
> - (unsigned long)ntohl(reply.magic));
> - return ERR_PTR(-EPROTO);
> + (unsigned long)ntohl(reply->magic));
> + return -EPROTO;
> }
>
> - memcpy(&handle, reply.handle, sizeof(handle));
> + return 0;
> +}
> +
> +/* NULL returned = something went wrong, inform userspace */
> +static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
> + struct nbd_reply *reply)
> +{
> + struct nbd_config *config = nbd->config;
> + int result;
> + struct nbd_cmd *cmd;
> + struct request *req = NULL;
> + u64 handle;
> + u16 hwq;
> + u32 tag;
> + struct iov_iter to;
> + int ret = 0;
> +
> + memcpy(&handle, reply->handle, sizeof(handle));
> tag = nbd_handle_to_tag(handle);
> hwq = blk_mq_unique_tag_to_hwq(tag);
> if (hwq < nbd->tag_set.nr_hw_queues)
> @@ -747,9 +756,9 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
> ret = -ENOENT;
> goto out;
> }
> - if (ntohl(reply.error)) {
> + if (ntohl(reply->error)) {
> dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
> - ntohl(reply.error));
> + ntohl(reply->error));
> cmd->status = BLK_STS_IOERR;
> goto out;
> }
> @@ -795,24 +804,36 @@ static void recv_work(struct work_struct *work)
> work);
> struct nbd_device *nbd = args->nbd;
> struct nbd_config *config = nbd->config;
> + struct request_queue *q = nbd->disk->queue;
> + struct nbd_sock *nsock;
> struct nbd_cmd *cmd;
> struct request *rq;
>
> while (1) {
> - cmd = nbd_read_stat(nbd, args->index);
> - if (IS_ERR(cmd)) {
> - struct nbd_sock *nsock = config->socks[args->index];
> + struct nbd_reply reply;
>
> - mutex_lock(&nsock->tx_lock);
> - nbd_mark_nsock_dead(nbd, nsock, 1);
> - mutex_unlock(&nsock->tx_lock);
> + if (nbd_read_reply(nbd, args->index, &reply))
> break;
> - }
>
> + if (!percpu_ref_tryget(&q->q_usage_counter))
> + break;
> +
> + cmd = nbd_handle_reply(nbd, args->index, &reply);
> + if (IS_ERR(cmd)) {
> + blk_queue_exit(q);
> + break;
> + }
> rq = blk_mq_rq_from_pdu(cmd);
> if (likely(!blk_should_fake_timeout(rq->q)))
> blk_mq_complete_request(rq);
> + blk_queue_exit(q);
> }
> +
> + nsock = config->socks[args->index];
> + mutex_lock(&nsock->tx_lock);
> + nbd_mark_nsock_dead(nbd, nsock, 1);
> + mutex_unlock(&nsock->tx_lock);
> +
> nbd_config_put(nbd);
> atomic_dec(&config->recv_threads);
> wake_up(&config->recv_wq);
>
>
> Thanks,
> Ming
>
> .
>
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