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: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 9e5f07f..47c6f9c 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3325,6 +3325,31 @@
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 @@
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 @@
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 @@
*/
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);