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block: fix double-free in the failure path of cgwb_bdi_init()
commit5f478e4ea5
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:a13f35e871
("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>
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1 changed files with 7 additions and 2 deletions
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@ -757,15 +757,20 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
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if (!bdi->wb_congested)
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return -ENOMEM;
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atomic_set(&bdi->wb_congested->refcnt, 1);
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err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
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if (err) {
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kfree(bdi->wb_congested);
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wb_congested_put(bdi->wb_congested);
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return err;
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}
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return 0;
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}
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static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
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static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
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{
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wb_congested_put(bdi->wb_congested);
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}
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#endif /* CONFIG_CGROUP_WRITEBACK */
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