| Message ID | 20210915081537.1684327-7-yukuai3@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | handle unexpected message from server | expand |
On Wed, Sep 15, 2021 at 04:15:37PM +0800, Yu Kuai wrote: > +++ b/block/blk-core.c > @@ -489,6 +489,7 @@ void blk_queue_exit(struct request_queue *q) > { > percpu_ref_put(&q->q_usage_counter); > } > +EXPORT_SYMBOL(blk_queue_exit); These needs to be an EXPORT_SYMBOL_GPL. But more importantly it needs to be a separate properly documented patch, and this function needs to grow a kerneldoc comment as well. > + /* > + * Get q_usage_counter can prevent accessing freed request > + * through blk_mq_tag_to_rq() in nbd_handle_reply(). If > + * q_usage_counter is zero, then no request is inflight, which > + * means something is wrong since we expect to find a request to > + * complete here. > + */ > + if (!percpu_ref_tryget(&q->q_usage_counter)) { > + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", > + __func__); > + break; > + } And this needs a properly documented wrapper as well. > + > cmd = nbd_handle_reply(nbd, args->index, &reply); > - if (IS_ERR(cmd)) > + 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); That being said I can't say I like how this exposed block layer internals. We don't really need a reference to the queue here anywhere, you just use it as a dumb debug check. If we really want to reuse (abuse?) q_usage_counter a helper to just grab a reference and immediately drop it might be a better fit.
On Wed, Sep 15, 2021 at 04:15:37PM +0800, Yu Kuai wrote: > There is a problem that nbd_handle_reply() might access freed request: > > 1) At first, a normal io is submitted and completed with scheduler: > > internel_tag = blk_mq_get_tag -> get tag from sched_tags > blk_mq_rq_ctx_init > sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] > ... > blk_mq_get_driver_tag > __blk_mq_get_driver_tag -> get tag from tags > tags->rq[tag] = sched_tag->static_rq[internel_tag] > > So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing > to the request: sched_tags->static_rq[internal_tag]. Even if the > io is finished. > > 2) nbd server send a reply with random tag directly: > > recv_work > nbd_handle_reply > blk_mq_tag_to_rq(tags, tag) > rq = tags->rq[tag] > > 3) if the sched_tags->static_rq is freed: > > blk_mq_sched_free_requests > blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i) > -> step 2) access rq before clearing rq mapping > blk_mq_clear_rq_mapping(set, tags, hctx_idx); > __free_pages() -> rq is freed here > > 4) Then, nbd continue to use the freed request in nbd_handle_reply > > Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(), > thus request is ensured not to be freed because 'q_usage_counter' is > not zero. > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > block/blk-core.c | 1 + > drivers/block/nbd.c | 19 ++++++++++++++++++- > 2 files changed, 19 insertions(+), 1 deletion(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 5454db2fa263..2008e6903166 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -489,6 +489,7 @@ void blk_queue_exit(struct request_queue *q) > { > percpu_ref_put(&q->q_usage_counter); > } > +EXPORT_SYMBOL(blk_queue_exit); > > static void blk_queue_usage_counter_release(struct percpu_ref *ref) > { > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index 9a7bbf8ebe74..f065afcc7586 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -824,6 +824,7 @@ 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; > @@ -834,13 +835,29 @@ static void recv_work(struct work_struct *work) > if (nbd_read_reply(nbd, args->index, &reply)) > break; > > + /* > + * Get q_usage_counter can prevent accessing freed request > + * through blk_mq_tag_to_rq() in nbd_handle_reply(). If > + * q_usage_counter is zero, then no request is inflight, which > + * means something is wrong since we expect to find a request to > + * complete here. > + */ > + if (!percpu_ref_tryget(&q->q_usage_counter)) { > + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", > + __func__); > + break; > + } > + > cmd = nbd_handle_reply(nbd, args->index, &reply); > - if (IS_ERR(cmd)) > + 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); You can simply call percpu_ref_put() directly just like what scsi_end_request() is doing.
On 2021/09/15 16:28, Ming Lei wrote: > On Wed, Sep 15, 2021 at 04:15:37PM +0800, Yu Kuai wrote: >> There is a problem that nbd_handle_reply() might access freed request: >> >> 1) At first, a normal io is submitted and completed with scheduler: >> >> internel_tag = blk_mq_get_tag -> get tag from sched_tags >> blk_mq_rq_ctx_init >> sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] >> ... >> blk_mq_get_driver_tag >> __blk_mq_get_driver_tag -> get tag from tags >> tags->rq[tag] = sched_tag->static_rq[internel_tag] >> >> So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing >> to the request: sched_tags->static_rq[internal_tag]. Even if the >> io is finished. >> >> 2) nbd server send a reply with random tag directly: >> >> recv_work >> nbd_handle_reply >> blk_mq_tag_to_rq(tags, tag) >> rq = tags->rq[tag] >> >> 3) if the sched_tags->static_rq is freed: >> >> blk_mq_sched_free_requests >> blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i) >> -> step 2) access rq before clearing rq mapping >> blk_mq_clear_rq_mapping(set, tags, hctx_idx); >> __free_pages() -> rq is freed here >> >> 4) Then, nbd continue to use the freed request in nbd_handle_reply >> >> Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(), >> thus request is ensured not to be freed because 'q_usage_counter' is >> not zero. >> >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> block/blk-core.c | 1 + >> drivers/block/nbd.c | 19 ++++++++++++++++++- >> 2 files changed, 19 insertions(+), 1 deletion(-) >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 5454db2fa263..2008e6903166 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -489,6 +489,7 @@ void blk_queue_exit(struct request_queue *q) >> { >> percpu_ref_put(&q->q_usage_counter); >> } >> +EXPORT_SYMBOL(blk_queue_exit); >> >> static void blk_queue_usage_counter_release(struct percpu_ref *ref) >> { >> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >> index 9a7bbf8ebe74..f065afcc7586 100644 >> --- a/drivers/block/nbd.c >> +++ b/drivers/block/nbd.c >> @@ -824,6 +824,7 @@ 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; >> @@ -834,13 +835,29 @@ static void recv_work(struct work_struct *work) >> if (nbd_read_reply(nbd, args->index, &reply)) >> break; >> >> + /* >> + * Get q_usage_counter can prevent accessing freed request >> + * through blk_mq_tag_to_rq() in nbd_handle_reply(). If >> + * q_usage_counter is zero, then no request is inflight, which >> + * means something is wrong since we expect to find a request to >> + * complete here. >> + */ >> + if (!percpu_ref_tryget(&q->q_usage_counter)) { >> + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", >> + __func__); >> + break; >> + } >> + >> cmd = nbd_handle_reply(nbd, args->index, &reply); >> - if (IS_ERR(cmd)) >> + 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); > > You can simply call percpu_ref_put() directly just like what scsi_end_request() > is doing. > Thanks for the adivce, will do that in next iteration. (hopefully the last) Best regards, Kuai
On 2021/09/15 16:20, Christoph Hellwig wrote: > On Wed, Sep 15, 2021 at 04:15:37PM +0800, Yu Kuai wrote: >> +++ b/block/blk-core.c >> @@ -489,6 +489,7 @@ void blk_queue_exit(struct request_queue *q) >> { >> percpu_ref_put(&q->q_usage_counter); >> } >> +EXPORT_SYMBOL(blk_queue_exit); > > These needs to be an EXPORT_SYMBOL_GPL. But more importantly it > needs to be a separate properly documented patch, and this function > needs to grow a kerneldoc comment as well. > >> + /* >> + * Get q_usage_counter can prevent accessing freed request >> + * through blk_mq_tag_to_rq() in nbd_handle_reply(). If >> + * q_usage_counter is zero, then no request is inflight, which >> + * means something is wrong since we expect to find a request to >> + * complete here. >> + */ >> + if (!percpu_ref_tryget(&q->q_usage_counter)) { >> + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", >> + __func__); >> + break; >> + } > > And this needs a properly documented wrapper as well. > >> + >> cmd = nbd_handle_reply(nbd, args->index, &reply); >> - if (IS_ERR(cmd)) >> + 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); > > That being said I can't say I like how this exposed block layer > internals. We don't really need a reference to the queue here > anywhere, you just use it as a dumb debug check. If we really want to > reuse (abuse?) q_usage_counter a helper to just grab a reference and > immediately drop it might be a better fit. > . Hi, The uaf is because blk_mq_sched_free_requests() can concurrent with nbd_read_stat(), and hold the ref during nbd_read_stat() can break the concurrency, thus the ref can't be dropped immediately. I'll use percpu_ref_put() directly as Ming suggestted. Thanks, Kuai
diff --git a/block/blk-core.c b/block/blk-core.c index 5454db2fa263..2008e6903166 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -489,6 +489,7 @@ void blk_queue_exit(struct request_queue *q) { percpu_ref_put(&q->q_usage_counter); } +EXPORT_SYMBOL(blk_queue_exit); static void blk_queue_usage_counter_release(struct percpu_ref *ref) { diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 9a7bbf8ebe74..f065afcc7586 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -824,6 +824,7 @@ 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; @@ -834,13 +835,29 @@ static void recv_work(struct work_struct *work) if (nbd_read_reply(nbd, args->index, &reply)) break; + /* + * Get q_usage_counter can prevent accessing freed request + * through blk_mq_tag_to_rq() in nbd_handle_reply(). If + * q_usage_counter is zero, then no request is inflight, which + * means something is wrong since we expect to find a request to + * complete here. + */ + if (!percpu_ref_tryget(&q->q_usage_counter)) { + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", + __func__); + break; + } + cmd = nbd_handle_reply(nbd, args->index, &reply); - if (IS_ERR(cmd)) + 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];
There is a problem that nbd_handle_reply() might access freed request: 1) At first, a normal io is submitted and completed with scheduler: internel_tag = blk_mq_get_tag -> get tag from sched_tags blk_mq_rq_ctx_init sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] ... blk_mq_get_driver_tag __blk_mq_get_driver_tag -> get tag from tags tags->rq[tag] = sched_tag->static_rq[internel_tag] So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing to the request: sched_tags->static_rq[internal_tag]. Even if the io is finished. 2) nbd server send a reply with random tag directly: recv_work nbd_handle_reply blk_mq_tag_to_rq(tags, tag) rq = tags->rq[tag] 3) if the sched_tags->static_rq is freed: blk_mq_sched_free_requests blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i) -> step 2) access rq before clearing rq mapping blk_mq_clear_rq_mapping(set, tags, hctx_idx); __free_pages() -> rq is freed here 4) Then, nbd continue to use the freed request in nbd_handle_reply Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(), thus request is ensured not to be freed because 'q_usage_counter' is not zero. Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- block/blk-core.c | 1 + drivers/block/nbd.c | 19 ++++++++++++++++++- 2 files changed, 19 insertions(+), 1 deletion(-)