writeback: Fix bdi use after free in wb_work_complete()
By the time bdi_work_on_stack gets evaluated again in bdi_work_free, it
can already have been deallocated and used for something else in the
!on stack case, giving a false positive in this test and causing
corruption.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 6bca6f8..7eba732 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -113,6 +113,7 @@
static void wb_work_complete(struct bdi_work *work)
{
const enum writeback_sync_modes sync_mode = work->args.sync_mode;
+ int onstack = bdi_work_on_stack(work);
/*
* For allocated work, we can clear the done/seen bit right here.
@@ -120,9 +121,9 @@
* to after the RCU grace period, since the stack could be invalidated
* as soon as bdi_work_clear() has done the wakeup.
*/
- if (!bdi_work_on_stack(work))
+ if (!onstack)
bdi_work_clear(work);
- if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
+ if (sync_mode == WB_SYNC_NONE || onstack)
call_rcu(&work->rcu_head, bdi_work_free);
}