Commit 9875201e authored by Josh Durgin's avatar Josh Durgin
Browse files

rbd: fix use-after free of rbd_dev->disk 

Removing a device deallocates the disk, unschedules the watch, and
finally cleans up the rbd_dev structure. rbd_dev_refresh(), called
from the watch callback, updates the disk size and rbd_dev
structure. With no locking between them, rbd_dev_refresh() may use the
device or rbd_dev after they've been freed.

To fix this, check whether RBD_DEV_FLAG_REMOVING is set before
updating the disk size in rbd_dev_refresh(). In order to prevent a
race where rbd_dev_refresh() is already revalidating the disk when
rbd_remove() is called, move the call to rbd_bus_del_dev() after the
watch is unregistered and all notifies are complete. It's safe to
defer deleting this structure because no new requests can be submitted
once the RBD_DEV_FLAG_REMOVING is set, since the device cannot be
opened.

Fixes: http://tracker.ceph.com/issues/5636


Signed-off-by: default avatarJosh Durgin <josh.durgin@inktank.com>
Reviewed-by: default avatarAlex Elder <elder@linaro.org>
parent 20e0af67

drivers/block/rbd.c

+33 −7
Original line number Diff line number Diff line
@@ -3325,6 +3325,31 @@ static void rbd_exists_validate(struct rbd_device *rbd_dev) 
		clear_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags);

}



static void rbd_dev_update_size(struct rbd_device *rbd_dev)

{

	sector_t size;

	bool removing;



	/*

	 * Don't hold the lock while doing disk operations,

	 * or lock ordering will conflict with the bdev mutex via:

	 * rbd_add() -> blkdev_get() -> rbd_open()

	 */

	spin_lock_irq(&rbd_dev->lock);

	removing = test_bit(RBD_DEV_FLAG_REMOVING, &rbd_dev->flags);

	spin_unlock_irq(&rbd_dev->lock);

	/*

	 * If the device is being removed, rbd_dev->disk has

	 * been destroyed, so don't try to update its size

	 */

	if (!removing) {

		size = (sector_t)rbd_dev->mapping.size / SECTOR_SIZE;

		dout("setting size to %llu sectors", (unsigned long long)size);

		set_capacity(rbd_dev->disk, size);

		revalidate_disk(rbd_dev->disk);

	}

}



static int rbd_dev_refresh(struct rbd_device *rbd_dev)

{

	u64 mapping_size;
@@ -3344,12 +3369,7 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev) 
	up_write(&rbd_dev->header_rwsem);



	if (mapping_size != rbd_dev->mapping.size) {

		sector_t size;



		size = (sector_t)rbd_dev->mapping.size / SECTOR_SIZE;

		dout("setting size to %llu sectors", (unsigned long long)size);

		set_capacity(rbd_dev->disk, size);

		revalidate_disk(rbd_dev->disk);

		rbd_dev_update_size(rbd_dev);

	}



	return ret;
@@ -5160,7 +5180,6 @@ static ssize_t rbd_remove(struct bus_type *bus, 
	if (ret < 0 || already)

		return ret;



	rbd_bus_del_dev(rbd_dev);

	ret = rbd_dev_header_watch_sync(rbd_dev, false);

	if (ret)

		rbd_warn(rbd_dev, "failed to cancel watch event (%d)\n", ret);
@@ -5171,6 +5190,13 @@ static ssize_t rbd_remove(struct bus_type *bus, 
	 */

	dout("%s: flushing notifies", __func__);

	ceph_osdc_flush_notifies(&rbd_dev->rbd_client->client->osdc);

	/*

	 * Don't free anything from rbd_dev->disk until after all

	 * notifies are completely processed. Otherwise

	 * rbd_bus_del_dev() will race with rbd_watch_cb(), resulting

	 * in a potential use after free of rbd_dev->disk or rbd_dev.

	 */

	rbd_bus_del_dev(rbd_dev);

	rbd_dev_image_release(rbd_dev);

	module_put(THIS_MODULE);

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