On 04/15/2016 10:26 AM, Ilya Dryomov wrote:
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:
[<ffffffffa0508344>] rbd_watch_cb+0x34/0x180 [rbd]
[<ffffffffa04bd290>] do_event_work+0x40/0xb0 [libceph]
[<ffffffff8109d5db>] process_one_work+0x17b/0x470
[<ffffffff8109e3ab>] worker_thread+0x11b/0x400
[<ffffffff8109e290>] ? rescuer_thread+0x400/0x400
[<ffffffff810a5acf>] kthread+0xcf/0xe0
[<ffffffff810b41b3>] ? finish_task_switch+0x53/0x170
[<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140
[<ffffffff81645dd8>] ret_from_fork+0x58/0x90
[<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140
RIP [<ffffffffa050828a>] 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:
[<ffffffff81cccee0>] ? rbd_parent_request_create+0x150/0x150
[<ffffffff81cd4e59>] rbd_dev_refresh+0x59/0x390
[<ffffffff81cd5229>] rbd_watch_cb+0x69/0x290
[<ffffffff81fde9bf>] do_event_work+0x10f/0x1c0
[<ffffffff81107799>] process_one_work+0x689/0x1a80
[<ffffffff811076f7>] ? process_one_work+0x5e7/0x1a80
[<ffffffff81132065>] ? finish_task_switch+0x225/0x640
[<ffffffff81107110>] ? pwq_dec_nr_in_flight+0x2b0/0x2b0
[<ffffffff81108c69>] worker_thread+0xd9/0x1320
[<ffffffff81108b90>] ? process_one_work+0x1a80/0x1a80
[<ffffffff8111b02d>] kthread+0x21d/0x2e0
[<ffffffff8111ae10>] ? kthread_stop+0x550/0x550
[<ffffffff82022802>] ret_from_fork+0x22/0x40
[<ffffffff8111ae10>] ? kthread_stop+0x550/0x550
RIP [<ffffffff81ccd8f9>] 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 <idryomov@xxxxxxxxx>
Looks good to me.
Reviewed-by: Josh Durgin <jdurgin@xxxxxxxxxx>
---
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 644940377954..9f1eb00b5e64 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);
@@ -5188,6 +5180,10 @@ 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;
@@ -5196,7 +5192,7 @@ 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);
@@ -5237,8 +5233,9 @@ 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);
@@ -5253,6 +5250,8 @@ 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;
}
@@ -5443,6 +5442,7 @@ 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;
@@ -5472,6 +5472,7 @@ 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);
@@ -5578,12 +5579,6 @@ 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
--
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