On Fri, Apr 12, 2019 at 01:03:35PM +0200, Hannes Reinecke wrote:

On 4/12/19 5:30 AM, Ming Lei wrote:

...

Once blk_cleanup_queue() returns, tags shouldn't be used any more, because blk_mq_free_tag_set() may be called. Commit 45a9c9d909b2 ("blk-mq: Fix a use-after-free") fixes this issue exactly.

However, that commit introduces another issue. Before 45a9c9d909b2, we are allowed to run queue during cleaning up queue if the queue's kobj refcount is held. After that commit, queue can't be run during queue cleaning up, otherwise oops can be triggered easily because some fields of hctx are freed by blk_mq_free_queue() in blk_cleanup_queue().

We have invented ways for addressing this kind of issue before, such as:

8dc765d438f1 ("SCSI: fix queue cleanup race before queue initialization is done") c2856ae2f315 ("blk-mq: quiesce queue before freeing queue")

But still can't cover all cases, recently James reports another such kind of issue:

https://marc.info/?l=linux-scsi&m=155389088124782&w=2

This issue can be quite hard to address by previous way, given scsi_run_queue() may run requeues for other LUNs.

Fixes the above issue by freeing hctx's resources in its release handler, and this way is safe becasue tags isn't needed for freeing such hctx resource.

This approach follows typical design pattern wrt. kobject's release handler.

Cc: Dongli Zhang dongli.zhang@oracle.com Cc: James Smart james.smart@broadcom.com Cc: Bart Van Assche bart.vanassche@wdc.com Cc: linux-scsi@vger.kernel.org, Cc: Martin K . Petersen martin.petersen@oracle.com, Cc: Christoph Hellwig hch@lst.de, Cc: James E . J . Bottomley jejb@linux.vnet.ibm.com, Cc: jianchao wang jianchao.w.wang@oracle.com Reported-by: James Smart james.smart@broadcom.com Fixes: 45a9c9d909b2 ("blk-mq: Fix a use-after-free") Cc: stable@vger.kernel.org Signed-off-by: Ming Lei ming.lei@redhat.com

---

block/blk-core.c | 2 +- block/blk-mq-sysfs.c | 6 ++++++ block/blk-mq.c | 8 ++------ block/blk-mq.h | 2 +- 4 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c index 6583d67f3e34..20298aa5a77c 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -374,7 +374,7 @@ void blk_cleanup_queue(struct request_queue *q) blk_exit_queue(q); if (queue_is_mq(q))

• blk_mq_free_queue(q);
  

• blk_mq_exit_queue(q);
  

  percpu_ref_exit(&q->q_usage_counter);

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 3f9c3f4ac44c..4040e62c3737 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -10,6 +10,7 @@ #include <linux/smp.h> #include <linux/blk-mq.h> +#include "blk.h" #include "blk-mq.h" #include "blk-mq-tag.h" @@ -33,6 +34,11 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj) { struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx, kobj);

• if (hctx->flags & BLK_MQ_F_BLOCKING)

• cleanup_srcu_struct(hctx->srcu);
  

• blk_free_flush_queue(hctx->fq);
• sbitmap_free(&hctx->ctx_map); free_cpumask_var(hctx->cpumask); kfree(hctx->ctxs); kfree(hctx);

diff --git a/block/blk-mq.c b/block/blk-mq.c index b512ba0cb359..afc9912e2e42 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2259,12 +2259,7 @@ static void blk_mq_exit_hctx(struct request_queue *q, if (set->ops->exit_hctx) set->ops->exit_hctx(hctx, hctx_idx);

• if (hctx->flags & BLK_MQ_F_BLOCKING)

• cleanup_srcu_struct(hctx->srcu);
  

• blk_mq_remove_cpuhp(hctx);
• blk_free_flush_queue(hctx->fq);
• sbitmap_free(&hctx->ctx_map); } static void blk_mq_exit_hw_queues(struct request_queue *q,

@@ -2899,7 +2894,8 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, } EXPORT_SYMBOL(blk_mq_init_allocated_queue); -void blk_mq_free_queue(struct request_queue *q) +/* tags can _not_ be used after returning from blk_mq_exit_queue */ +void blk_mq_exit_queue(struct request_queue *q) { struct blk_mq_tag_set *set = q->tag_set; diff --git a/block/blk-mq.h b/block/blk-mq.h index d704fc7766f4..c421e3a16e36 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -37,7 +37,7 @@ struct blk_mq_ctx { struct kobject kobj; } ____cacheline_aligned_in_smp; -void blk_mq_free_queue(struct request_queue *q); +void blk_mq_exit_queue(struct request_queue *q); int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr); void blk_mq_wake_waiters(struct request_queue *q); bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);

Hmm. While this is a good point, I'm somehow not convinced that it fixes the mentioned problem.

This patch fixes the following generic issue in block layer:

1) usually any block layer API may be called safely when the request queue's refcount is held

2) when blk_cleanup_queue() is run, no use-after-free oops can be triggered on the code path in 1)

For the sbitmap_any_set() case, the problem appears to be the racy interaction between nvme_scan_queues() and nvme_reset_ctrl(). Both can (and do) run in parallel, and as nvme_scan_queue() is not able to update the nvme namespace list race-free (nvme_ns_remove() will kill the namespace before removing it from the queue) we'll hit issues where nvme_start_queues() is called on namespaces which are halfway through nvme_ns_remove(), causing all sorts of issues.

This is one race between nvme reset and scan, and especially the refcount of ns queue isn't held before calling nvme_stop_queues() and nvme_start_queues().

The above situation is one NVMe specific issue and doesn't belong to what this patch tries to address.

See "[PATCHv2 RFC] nvme: use nvme_set_queue_dying() during namespace rescanning" for my attempt to fix this. That patch is actually not complete; there is another one under testing currently to not remove namespaces at all during nvme_reset_ctrl(), but results are not in yet.

Otherwise:

Looks the above 'Otherwise' shouldn't be needed, as I explained.

Reviewed-by: Hannes Reinecke hare@suse.com

Thanks!