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58 lines
1.8 KiB
Diff
58 lines
1.8 KiB
Diff
From 5f478e4ea5c5560b4e40eb136991a09f9389f331 Mon Sep 17 00:00:00 2001
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From: Tejun Heo <tj@kernel.org>
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Date: Wed, 8 Feb 2017 15:19:07 -0500
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Subject: block: fix double-free in the failure path of cgwb_bdi_init()
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From: Tejun Heo <tj@kernel.org>
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commit 5f478e4ea5c5560b4e40eb136991a09f9389f331 upstream.
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When !CONFIG_CGROUP_WRITEBACK, bdi has single bdi_writeback_congested
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at bdi->wb_congested. cgwb_bdi_init() allocates it with kzalloc() and
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doesn't do further initialization. This usually works fine as the
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reference count gets bumped to 1 by wb_init() and the put from
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wb_exit() releases it.
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However, when wb_init() fails, it puts the wb base ref automatically
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freeing the wb and the explicit kfree() in cgwb_bdi_init() error path
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ends up trying to free the same pointer the second time causing a
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double-free.
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Fix it by explicitly initilizing the refcnt to 1 and putting the base
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ref from cgwb_bdi_destroy().
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Signed-off-by: Tejun Heo <tj@kernel.org>
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Reported-by: Dmitry Vyukov <dvyukov@google.com>
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Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback")
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Signed-off-by: Jens Axboe <axboe@fb.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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mm/backing-dev.c | 9 +++++++--
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1 file changed, 7 insertions(+), 2 deletions(-)
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--- a/mm/backing-dev.c
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+++ b/mm/backing-dev.c
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@@ -757,15 +757,20 @@ static int cgwb_bdi_init(struct backing_
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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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+
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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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