Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 30/32] block: fix double-free in the failure path of cgwb_bdi_init() | Date | Fri, 24 Feb 2017 09:38:14 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo <tj@kernel.org>
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>
--- mm/backing-dev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -757,15 +757,20 @@ static int cgwb_bdi_init(struct backing_ 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 */
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