Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Wed, 8 Feb 2017 15:19:07 -0500 | From | Tejun Heo <> | Subject | [PATCH] block: fix double-free in the failure path of cgwb_bdi_init() |
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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") Cc: stable@vger.kernel.org # v4.2+ --- Hello,
ISTR seeing another fix for this bug but can't find it right now. If I'm imagining things, please apply this one. If not, either one is fine.
Thanks.
mm/backing-dev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 3bfed5ab..61b3407 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); +} #endif /* CONFIG_CGROUP_WRITEBACK */
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