From 5f478e4ea5c5560b4e40eb136991a09f9389f331 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 8 Feb 2017 15:19:07 -0500 Subject: 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: stable@vger.kernel.org # v4.2+ Signed-off-by: Jens Axboe --- mm/backing-dev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'mm/backing-dev.c') 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); +} #endif /* CONFIG_CGROUP_WRITEBACK */ -- cgit v1.2.3-59-g8ed1b