diff options
authorTejun Heo <>2017-02-08 15:19:07 -0500
committerJens Axboe <>2017-02-08 13:52:01 -0700
commit5f478e4ea5c5560b4e40eb136991a09f9389f331 (patch)
parentb35ba01ea6979125e9c23fb322517748278f15e6 (diff)
block: fix double-free in the failure path of cgwb_bdi_init()
When !CONFIG_CGROUP_WRITEBACK, bdi has single bdi_writeback_congested at bdi->wb_congested. cgwb_bdi_init() allocates it with kzalloc() and doesn't do further initialization. This usually works fine as the reference count gets bumped to 1 by wb_init() and the put from wb_exit() releases it. However, when wb_init() fails, it puts the wb base ref automatically freeing the wb and the explicit kfree() in cgwb_bdi_init() error path ends up trying to free the same pointer the second time causing a double-free. Fix it by explicitly initilizing the refcnt to 1 and putting the base ref from cgwb_bdi_destroy(). Signed-off-by: Tejun Heo <> Reported-by: Dmitry Vyukov <> Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") Cc: # v4.2+ Signed-off-by: Jens Axboe <>
1 files changed, 7 insertions, 2 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 28ce6cf7b2ff..39ce616a9d71 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -759,15 +759,20 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
if (!bdi->wb_congested)
return -ENOMEM;
+ atomic_set(&bdi->wb_congested->refcnt, 1);
err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
if (err) {
- kfree(bdi->wb_congested);
+ wb_congested_put(bdi->wb_congested);
return err;
return 0;
-static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
+static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
+ wb_congested_put(bdi->wb_congested);