| Message ID | 20210809030927.1946162-3-yukuai3@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fix request uaf in nbd_read_stat() | expand |
On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: > blk_mq_tag_to_rq() might return freed request, use > blk_mq_get_rq_by_tag() instead. > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > drivers/block/nbd.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index c38317979f74..9e56975a8eee 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > tag = nbd_handle_to_tag(handle); > hwq = blk_mq_unique_tag_to_hwq(tag); > if (hwq < nbd->tag_set.nr_hw_queues) > - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], > - blk_mq_unique_tag_to_tag(tag)); > - if (!req || !blk_mq_request_started(req)) { > - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", > - tag, req); > + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], > + blk_mq_unique_tag_to_tag(tag)); > + if (!req) { > + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); > return ERR_PTR(-ENOENT); > } > trace_nbd_header_received(req, handle); > @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > } > out: > trace_nbd_payload_received(req, handle); > + if (req) > + blk_mq_put_rq_ref(req); > mutex_unlock(&cmd->lock); > return ret ? ERR_PTR(ret) : cmd; After blk_mq_put_rq_ref() returns, this request may have been freed, so the returned 'cmd' may have been freed too. As I replied in your another thread, it is driver's responsibility to cover race between normal completion and timeout/error handling, that means the caller of blk_mq_tag_to_rq need to make sure that the request represented by the passed 'tag' can't be freed. I'd suggest to understand why nbd_read_stat()/blk_mq_tag_to_rq() may return one freed request first, who frees the request and how when calling blk_mq_tag_to_rq() before figuring out solutions. Thanks, Ming
On 2021/08/09 14:28, Ming Lei wrote: > On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: >> blk_mq_tag_to_rq() might return freed request, use >> blk_mq_get_rq_by_tag() instead. >> >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> drivers/block/nbd.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >> index c38317979f74..9e56975a8eee 100644 >> --- a/drivers/block/nbd.c >> +++ b/drivers/block/nbd.c >> @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) >> tag = nbd_handle_to_tag(handle); >> hwq = blk_mq_unique_tag_to_hwq(tag); >> if (hwq < nbd->tag_set.nr_hw_queues) >> - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], >> - blk_mq_unique_tag_to_tag(tag)); >> - if (!req || !blk_mq_request_started(req)) { >> - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", >> - tag, req); >> + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], >> + blk_mq_unique_tag_to_tag(tag)); >> + if (!req) { >> + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); >> return ERR_PTR(-ENOENT); >> } >> trace_nbd_header_received(req, handle); >> @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) >> } >> out: >> trace_nbd_payload_received(req, handle); >> + if (req) >> + blk_mq_put_rq_ref(req); >> mutex_unlock(&cmd->lock); >> return ret ? ERR_PTR(ret) : cmd; > > After blk_mq_put_rq_ref() returns, this request may have been freed, > so the returned 'cmd' may have been freed too. > > As I replied in your another thread, it is driver's responsibility to > cover race between normal completion and timeout/error handling, that > means the caller of blk_mq_tag_to_rq need to make sure that the request > represented by the passed 'tag' can't be freed. Hi, Ming There are two problems here in nbd, both reported by our syzkaller. The first is that blk_mq_tag_to_rq() returned a freed request, which is because tags->static_rq[] is freed without clearing tags->rq[]. Syzkaller log shows that a reply package is sent to client without the client's request package. And this patch is trying to solve this problem. The second is that flush_end_io() decrement it's refcount to -1. I guess this is because nbd_clear_que concurrent with normal completion / timeout / error handling, and somehow trigger the problem. However I'm still trying to understand the logic in nbd. I tried to add a check in flush_end_io() to fix this, as you replied, it's driver's responsibility to fix the problem. It seems that the two problems are not related. And this patch is ok to fix the first problem. Any suggestions? Thanks Kuai > > I'd suggest to understand why nbd_read_stat()/blk_mq_tag_to_rq() may return > one freed request first, who frees the request and how when calling > blk_mq_tag_to_rq() before figuring out solutions.
On Mon, Aug 09, 2021 at 03:08:26PM +0800, yukuai (C) wrote: > On 2021/08/09 14:28, Ming Lei wrote: > > On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: > > > blk_mq_tag_to_rq() might return freed request, use > > > blk_mq_get_rq_by_tag() instead. > > > > > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > > > --- > > > drivers/block/nbd.c | 11 ++++++----- > > > 1 file changed, 6 insertions(+), 5 deletions(-) > > > > > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > > > index c38317979f74..9e56975a8eee 100644 > > > --- a/drivers/block/nbd.c > > > +++ b/drivers/block/nbd.c > > > @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > > > tag = nbd_handle_to_tag(handle); > > > hwq = blk_mq_unique_tag_to_hwq(tag); > > > if (hwq < nbd->tag_set.nr_hw_queues) > > > - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], > > > - blk_mq_unique_tag_to_tag(tag)); > > > - if (!req || !blk_mq_request_started(req)) { > > > - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", > > > - tag, req); > > > + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], > > > + blk_mq_unique_tag_to_tag(tag)); > > > + if (!req) { > > > + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); > > > return ERR_PTR(-ENOENT); > > > } > > > trace_nbd_header_received(req, handle); > > > @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > > > } > > > out: > > > trace_nbd_payload_received(req, handle); > > > + if (req) > > > + blk_mq_put_rq_ref(req); > > > mutex_unlock(&cmd->lock); > > > return ret ? ERR_PTR(ret) : cmd; > > > > After blk_mq_put_rq_ref() returns, this request may have been freed, > > so the returned 'cmd' may have been freed too. > > > > As I replied in your another thread, it is driver's responsibility to > > cover race between normal completion and timeout/error handling, that > > means the caller of blk_mq_tag_to_rq need to make sure that the request > > represented by the passed 'tag' can't be freed. > > Hi, Ming > > There are two problems here in nbd, both reported by our syzkaller. > > The first is that blk_mq_tag_to_rq() returned a freed request, which is > because tags->static_rq[] is freed without clearing tags->rq[]. > Syzkaller log shows that a reply package is sent to client without > the client's request package. And this patch is trying to solve this > problem. It is still driver's problem: ->static_rq is freed in blk_mq_free_tag_set() which is called after blk_cleanup_disk() returns. Once blk_cleanup_disk() returns, there shouldn't be any driver activity, including calling blk_mq_tag_to_rq() by passing one invalid tag. Thanks, Ming
On 2021/08/09 17:46, Ming Lei wrote: > On Mon, Aug 09, 2021 at 03:08:26PM +0800, yukuai (C) wrote: >> On 2021/08/09 14:28, Ming Lei wrote: >>> On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: >>>> blk_mq_tag_to_rq() might return freed request, use >>>> blk_mq_get_rq_by_tag() instead. >>>> >>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >>>> --- >>>> drivers/block/nbd.c | 11 ++++++----- >>>> 1 file changed, 6 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >>>> index c38317979f74..9e56975a8eee 100644 >>>> --- a/drivers/block/nbd.c >>>> +++ b/drivers/block/nbd.c >>>> @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) >>>> tag = nbd_handle_to_tag(handle); >>>> hwq = blk_mq_unique_tag_to_hwq(tag); >>>> if (hwq < nbd->tag_set.nr_hw_queues) >>>> - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], >>>> - blk_mq_unique_tag_to_tag(tag)); >>>> - if (!req || !blk_mq_request_started(req)) { >>>> - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", >>>> - tag, req); >>>> + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], >>>> + blk_mq_unique_tag_to_tag(tag)); >>>> + if (!req) { >>>> + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); >>>> return ERR_PTR(-ENOENT); >>>> } >>>> trace_nbd_header_received(req, handle); >>>> @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) >>>> } >>>> out: >>>> trace_nbd_payload_received(req, handle); >>>> + if (req) >>>> + blk_mq_put_rq_ref(req); >>>> mutex_unlock(&cmd->lock); >>>> return ret ? ERR_PTR(ret) : cmd; >>> >>> After blk_mq_put_rq_ref() returns, this request may have been freed, >>> so the returned 'cmd' may have been freed too. >>> >>> As I replied in your another thread, it is driver's responsibility to >>> cover race between normal completion and timeout/error handling, that >>> means the caller of blk_mq_tag_to_rq need to make sure that the request >>> represented by the passed 'tag' can't be freed. >> >> Hi, Ming >> >> There are two problems here in nbd, both reported by our syzkaller. >> >> The first is that blk_mq_tag_to_rq() returned a freed request, which is >> because tags->static_rq[] is freed without clearing tags->rq[]. >> Syzkaller log shows that a reply package is sent to client without >> the client's request package. And this patch is trying to solve this >> problem. > > It is still driver's problem: > > ->static_rq is freed in blk_mq_free_tag_set() which is called after > blk_cleanup_disk() returns. Once blk_cleanup_disk() returns, there > shouldn't be any driver activity, including calling blk_mq_tag_to_rq() > by passing one invalid tag. > Hi, Ming I understand if static_rq is freed through blk_mq_free_tag_set(), drivers should not use static_rq anymore. By the way, I was thinking about another path: blk_mq_update_nr_requests if (!hctx->sched_tags) -> if this is true ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr, false) blk_mq_free_rqs -> static_rq is freed here If this path concurrent with nbd_read_stat(), nbd_read_stat() can get a freed request by blk_mq_tag_to_rq(), since tags->lock is not held. t1: nbd_read_stat t2: blk_mq_update_nr_requests rq = blk_mq_tag_to_rq() blk_mq_free_rqs By holding tags->lock, we can check that rq state is idle, and it's ref is 0. Thanks Kuai
On Mon, Aug 09, 2021 at 10:04:32PM +0800, yukuai (C) wrote: > On 2021/08/09 17:46, Ming Lei wrote: > > On Mon, Aug 09, 2021 at 03:08:26PM +0800, yukuai (C) wrote: > > > On 2021/08/09 14:28, Ming Lei wrote: > > > > On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: > > > > > blk_mq_tag_to_rq() might return freed request, use > > > > > blk_mq_get_rq_by_tag() instead. > > > > > > > > > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > > > > > --- > > > > > drivers/block/nbd.c | 11 ++++++----- > > > > > 1 file changed, 6 insertions(+), 5 deletions(-) > > > > > > > > > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > > > > > index c38317979f74..9e56975a8eee 100644 > > > > > --- a/drivers/block/nbd.c > > > > > +++ b/drivers/block/nbd.c > > > > > @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > > > > > tag = nbd_handle_to_tag(handle); > > > > > hwq = blk_mq_unique_tag_to_hwq(tag); > > > > > if (hwq < nbd->tag_set.nr_hw_queues) > > > > > - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], > > > > > - blk_mq_unique_tag_to_tag(tag)); > > > > > - if (!req || !blk_mq_request_started(req)) { > > > > > - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", > > > > > - tag, req); > > > > > + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], > > > > > + blk_mq_unique_tag_to_tag(tag)); > > > > > + if (!req) { > > > > > + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); > > > > > return ERR_PTR(-ENOENT); > > > > > } > > > > > trace_nbd_header_received(req, handle); > > > > > @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > > > > > } > > > > > out: > > > > > trace_nbd_payload_received(req, handle); > > > > > + if (req) > > > > > + blk_mq_put_rq_ref(req); > > > > > mutex_unlock(&cmd->lock); > > > > > return ret ? ERR_PTR(ret) : cmd; > > > > > > > > After blk_mq_put_rq_ref() returns, this request may have been freed, > > > > so the returned 'cmd' may have been freed too. > > > > > > > > As I replied in your another thread, it is driver's responsibility to > > > > cover race between normal completion and timeout/error handling, that > > > > means the caller of blk_mq_tag_to_rq need to make sure that the request > > > > represented by the passed 'tag' can't be freed. > > > > > > Hi, Ming > > > > > > There are two problems here in nbd, both reported by our syzkaller. > > > > > > The first is that blk_mq_tag_to_rq() returned a freed request, which is > > > because tags->static_rq[] is freed without clearing tags->rq[]. > > > Syzkaller log shows that a reply package is sent to client without > > > the client's request package. And this patch is trying to solve this > > > problem. > > > > It is still driver's problem: > > > > ->static_rq is freed in blk_mq_free_tag_set() which is called after > > blk_cleanup_disk() returns. Once blk_cleanup_disk() returns, there > > shouldn't be any driver activity, including calling blk_mq_tag_to_rq() > > by passing one invalid tag. > > > > Hi, Ming > > I understand if static_rq is freed through blk_mq_free_tag_set(), > drivers should not use static_rq anymore. > > By the way, I was thinking about another path: > > blk_mq_update_nr_requests > if (!hctx->sched_tags) -> if this is true > ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr, false) > blk_mq_free_rqs -> static_rq is freed here > > If this path concurrent with nbd_read_stat(), nbd_read_stat() can > get a freed request by blk_mq_tag_to_rq(), since tags->lock is not > held. > > t1: nbd_read_stat t2: blk_mq_update_nr_requests > rq = blk_mq_tag_to_rq() > blk_mq_free_rqs t1 isn't supposed to happen when t2 is running. blk_mq_update_nr_requests() is only called by nbd_start_device(). nbd_start_device(): if (nbd->task_recv) return -EBUSY; ... nbd->recv_workq = alloc_workqueue() That means nbd_config_put() has been called and ->config_refs has dropped to zero, so socket has been shutdown, and ->recv_workq has been destroyed, so t1 isn't supposed to happen when t2 is running. > > By holding tags->lock, we can check that rq state is idle, and it's > ref is 0. Firstly tags->lock can't fix the race[1], secondly it should be addressed in driver. [1] https://lore.kernel.org/linux-block/20210809030927.1946162-2-yukuai3@huawei.com/T/#m6651289c5718b45a8ae8a7efc889248f8cb904a3 Thanks, Ming
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index c38317979f74..9e56975a8eee 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) tag = nbd_handle_to_tag(handle); hwq = blk_mq_unique_tag_to_hwq(tag); if (hwq < nbd->tag_set.nr_hw_queues) - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], - blk_mq_unique_tag_to_tag(tag)); - if (!req || !blk_mq_request_started(req)) { - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", - tag, req); + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], + blk_mq_unique_tag_to_tag(tag)); + if (!req) { + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); return ERR_PTR(-ENOENT); } trace_nbd_header_received(req, handle); @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) } out: trace_nbd_payload_received(req, handle); + if (req) + blk_mq_put_rq_ref(req); mutex_unlock(&cmd->lock); return ret ? ERR_PTR(ret) : cmd; }
blk_mq_tag_to_rq() might return freed request, use blk_mq_get_rq_by_tag() instead. Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- drivers/block/nbd.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)