From 811c6688774613a78bfa020f64b570b73f6974c8 Mon Sep 17 00:00:00 2001 From: Ilya Dryomov Date: Fri, 15 Apr 2016 16:22:16 +0200 Subject: [PATCH] rbd: fix rbd map vs notify races A while ago, commit 9875201e1049 ("rbd: fix use-after free of rbd_dev->disk") fixed rbd unmap vs notify race by introducing an exported wrapper for flushing notifies and sticking it into do_rbd_remove(). A similar problem exists on the rbd map path, though: the watch is registered in rbd_dev_image_probe(), while the disk is set up quite a few steps later, in rbd_dev_device_setup(). Nothing prevents a notify from coming in and crashing on a NULL rbd_dev->disk: BUG: unable to handle kernel NULL pointer dereference at 0000000000000050 Call Trace: [] rbd_watch_cb+0x34/0x180 [rbd] [] do_event_work+0x40/0xb0 [libceph] [] process_one_work+0x17b/0x470 [] worker_thread+0x11b/0x400 [] ? rescuer_thread+0x400/0x400 [] kthread+0xcf/0xe0 [] ? finish_task_switch+0x53/0x170 [] ? kthread_create_on_node+0x140/0x140 [] ret_from_fork+0x58/0x90 [] ? kthread_create_on_node+0x140/0x140 RIP [] rbd_dev_refresh+0xfa/0x180 [rbd] If an error occurs during rbd map, we have to error out, potentially tearing down a watch. Just like on rbd unmap, notifies have to be flushed, otherwise rbd_watch_cb() may end up trying to read in the image header after rbd_dev_image_release() has run: Assertion failure in rbd_dev_header_info() at line 4722: rbd_assert(rbd_image_format_valid(rbd_dev->image_format)); Call Trace: [] ? rbd_parent_request_create+0x150/0x150 [] rbd_dev_refresh+0x59/0x390 [] rbd_watch_cb+0x69/0x290 [] do_event_work+0x10f/0x1c0 [] process_one_work+0x689/0x1a80 [] ? process_one_work+0x5e7/0x1a80 [] ? finish_task_switch+0x225/0x640 [] ? pwq_dec_nr_in_flight+0x2b0/0x2b0 [] worker_thread+0xd9/0x1320 [] ? process_one_work+0x1a80/0x1a80 [] kthread+0x21d/0x2e0 [] ? kthread_stop+0x550/0x550 [] ret_from_fork+0x22/0x40 [] ? kthread_stop+0x550/0x550 RIP [] rbd_dev_header_info+0xa19/0x1e30 To fix this, a) check if RBD_DEV_FLAG_EXISTS is set before calling revalidate_disk(), b) move ceph_osdc_flush_notifies() call into rbd_dev_header_unwatch_sync() to cover rbd map error paths and c) turn header read-in into a critical section. The latter also happens to take care of rbd map foo@bar vs rbd snap rm foo@bar race. Fixes: http://tracker.ceph.com/issues/15490 Signed-off-by: Ilya Dryomov Reviewed-by: Josh Durgin --- drivers/block/rbd.c | 43 +++++++++++++++++++------------------------ 1 file changed, 19 insertions(+), 24 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 94a1843b0426..25d22da47f6e 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -538,7 +538,6 @@ static int _rbd_dev_v2_snap_size(struct rbd_device *rbd_dev, u64 snap_id, u8 *order, u64 *snap_size); static int _rbd_dev_v2_snap_features(struct rbd_device *rbd_dev, u64 snap_id, u64 *snap_features); -static u64 rbd_snap_id_by_name(struct rbd_device *rbd_dev, const char *name); static int rbd_open(struct block_device *bdev, fmode_t mode) { @@ -3127,9 +3126,6 @@ static void rbd_watch_cb(u64 ver, u64 notify_id, u8 opcode, void *data) struct rbd_device *rbd_dev = (struct rbd_device *)data; int ret; - if (!rbd_dev) - return; - dout("%s: \"%s\" notify_id %llu opcode %u\n", __func__, rbd_dev->header_name, (unsigned long long)notify_id, (unsigned int)opcode); @@ -3263,6 +3259,9 @@ static void rbd_dev_header_unwatch_sync(struct rbd_device *rbd_dev) ceph_osdc_cancel_event(rbd_dev->watch_event); rbd_dev->watch_event = NULL; + + dout("%s flushing notifies\n", __func__); + ceph_osdc_flush_notifies(&rbd_dev->rbd_client->client->osdc); } /* @@ -3642,21 +3641,14 @@ static void rbd_exists_validate(struct rbd_device *rbd_dev) 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() + * If EXISTS is not set, rbd_dev->disk may be NULL, so don't + * try to update its size. If REMOVING is set, updating size + * is just useless work since the device can't be opened. */ - 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) { + if (test_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags) && + !test_bit(RBD_DEV_FLAG_REMOVING, &rbd_dev->flags)) { 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); @@ -5187,6 +5179,10 @@ out_err: return ret; } +/* + * rbd_dev->header_rwsem must be locked for write and will be unlocked + * upon return. + */ static int rbd_dev_device_setup(struct rbd_device *rbd_dev) { int ret; @@ -5195,7 +5191,7 @@ static int rbd_dev_device_setup(struct rbd_device *rbd_dev) ret = rbd_dev_id_get(rbd_dev); if (ret) - return ret; + goto err_out_unlock; BUILD_BUG_ON(DEV_NAME_LEN < sizeof (RBD_DRV_NAME) + MAX_INT_FORMAT_WIDTH); @@ -5236,8 +5232,9 @@ static int rbd_dev_device_setup(struct rbd_device *rbd_dev) /* Everything's ready. Announce the disk to the world. */ set_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags); - add_disk(rbd_dev->disk); + up_write(&rbd_dev->header_rwsem); + add_disk(rbd_dev->disk); pr_info("%s: added with size 0x%llx\n", rbd_dev->disk->disk_name, (unsigned long long) rbd_dev->mapping.size); @@ -5252,6 +5249,8 @@ err_out_blkdev: unregister_blkdev(rbd_dev->major, rbd_dev->name); err_out_id: rbd_dev_id_put(rbd_dev); +err_out_unlock: + up_write(&rbd_dev->header_rwsem); return ret; } @@ -5442,6 +5441,7 @@ static ssize_t do_rbd_add(struct bus_type *bus, spec = NULL; /* rbd_dev now owns this */ rbd_opts = NULL; /* rbd_dev now owns this */ + down_write(&rbd_dev->header_rwsem); rc = rbd_dev_image_probe(rbd_dev, 0); if (rc < 0) goto err_out_rbd_dev; @@ -5471,6 +5471,7 @@ out: return rc; err_out_rbd_dev: + up_write(&rbd_dev->header_rwsem); rbd_dev_destroy(rbd_dev); err_out_client: rbd_put_client(rbdc); @@ -5577,12 +5578,6 @@ static ssize_t do_rbd_remove(struct bus_type *bus, return ret; rbd_dev_header_unwatch_sync(rbd_dev); - /* - * flush remaining watch callbacks - these must be complete - * before the osd_client is shutdown - */ - 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 -- 2.20.1