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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 <tj@kernel.org>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: a13f35e871 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2017-02-08 15:19:07 -05:00 committed by Jens Axboe
parent b35ba01ea6
commit 5f478e4ea5
1 changed files with 7 additions and 2 deletions
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9
mm/backing-dev.c
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@ -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 */