The violation of atomicity occurs when the brbd_uuid_set_bm function is executed simultaneously with modifying the value of device->ldev->md.uuid[UI_BITMAP]. Consider a scenario where, while device->ldev->md.uuid[UI_BITMAP] passes the validity check when its value is not zero, the value of device->ldev->md.uuid[UI_BITMAP] is written to zero. In this case, the check in brbd_uuid_set_bm might refer to the old value of device->ldev->md.uuid[UI_BITMAP] (before locking), which allows an invalid value to pass the validity check, resulting in inconsistency.
To address this issue, it is recommended to include the data validity check within the locked section of the function. This modification ensures that the value of device->ldev->md.uuid[UI_BITMAP] does not change during the validation process, thereby maintaining its integrity.
This possible bug is found by an experimental static analysis tool developed by our team. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations.
Fixes: 9f2247bb9b75 ("drbd: Protect accesses to the uuid set with a spinlock") Cc: stable@vger.kernel.org Signed-off-by: Qiu-ji Chen chenqiuji666@gmail.com --- drivers/block/drbd/drbd_main.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c index a9e49b212341..abafc4edf9ed 100644 --- a/drivers/block/drbd/drbd_main.c +++ b/drivers/block/drbd/drbd_main.c @@ -3399,10 +3399,12 @@ void drbd_uuid_new_current(struct drbd_device *device) __must_hold(local) void drbd_uuid_set_bm(struct drbd_device *device, u64 val) __must_hold(local) { unsigned long flags; - if (device->ldev->md.uuid[UI_BITMAP] == 0 && val == 0) + spin_lock_irqsave(&device->ldev->md.uuid_lock, flags); + if (device->ldev->md.uuid[UI_BITMAP] == 0 && val == 0) { + spin_unlock_irqrestore(&device->ldev->md.uuid_lock, flags); return; + }
- spin_lock_irqsave(&device->ldev->md.uuid_lock, flags); if (val == 0) { drbd_uuid_move_history(device); device->ldev->md.uuid[UI_HISTORY_START] = device->ldev->md.uuid[UI_BITMAP];