From: Yunjian Wang wangyunjian@huawei.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@huawei.com Suggested-by: Maxim Mikityanskiy maximmi@nvidia.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.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); } }