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authorTejun Heo <tj@kernel.org>2017-02-08 15:19:07 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-02-26 11:09:19 +0100
commitdea972f381a12fa0f4026a6eb6070a4fe6fb0465 (patch)
parent96081d826cb3ef1c911e49a3f84cc24ded9bcbf2 (diff)
block: fix double-free in the failure path of cgwb_bdi_init()
commit 5f478e4ea5c5560b4e40eb136991a09f9389f331 upstream. 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: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 7 insertions, 2 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 3bfed5ab2475..61b34071e3ee 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -758,15 +758,20 @@ 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);