linux-kernel - [PATCH 5.12 058/161] sch_htb: fix refcount leak in htb_parent_to_leaf

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Date:   Tue,  8 Jun 2021 20:26:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yunjian Wang <wangyunjian@...wei.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.12 058/161] sch_htb: fix refcount leak in htb_parent_to_leaf_offload

From: Yunjian Wang <wangyunjian@...wei.com>

[ Upstream commit 944d671d5faa0d78980a3da5c0f04960ef1ad893 ]

The commit ae81feb7338c ("sch_htb: fix null pointer dereference
on a null new_q") fixes a NULL pointer dereference bug, but it
is not correct.

Because htb_graft_helper properly handles the case when new_q
is NULL, and after the previous patch by skipping this call
which creates an inconsistency : dev_queue->qdisc will still
point to the old qdisc, but cl->parent->leaf.q will point to
the new one (which will be noop_qdisc, because new_q was NULL).
The code is based on an assumption that these two pointers are
the same, so it can lead to refcount leaks.

The correct fix is to add a NULL pointer check to protect
qdisc_refcount_inc inside htb_parent_to_leaf_offload.

Fixes: ae81feb7338c ("sch_htb: fix null pointer dereference on a null new_q")
Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
Suggested-by: Maxim Mikityanskiy <maximmi@...dia.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/sched/sch_htb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 081c11d5717c..8827987ba903 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1488,7 +1488,8 @@ static void htb_parent_to_leaf_offload(struct Qdisc *sch,
 	struct Qdisc *old_q;
 
 	/* One ref for cl->leaf.q, the other for dev_queue->qdisc. */
-	qdisc_refcount_inc(new_q);
+	if (new_q)
+		qdisc_refcount_inc(new_q);
 	old_q = htb_graft_helper(dev_queue, new_q);
 	WARN_ON(!(old_q->flags & TCQ_F_BUILTIN));
 }
@@ -1675,10 +1676,9 @@ static int htb_delete(struct Qdisc *sch, unsigned long arg,
 					  cl->parent->common.classid,
 					  NULL);
 		if (q->offload) {
-			if (new_q) {
+			if (new_q)
 				htb_set_lockdep_class_child(new_q);
-				htb_parent_to_leaf_offload(sch, dev_queue, new_q);
-			}
+			htb_parent_to_leaf_offload(sch, dev_queue, new_q);
 		}
 	}
 
-- 
2.30.2