sch_htb: fix refcount leak in htb_parent_to_leaf_offload
authorYunjian Wang <wangyunjian@huawei.com>
Fri, 4 Jun 2021 11:03:18 +0000 (19:03 +0800)
committerDavid S. Miller <davem@davemloft.net>
Fri, 4 Jun 2021 21:44:18 +0000 (14:44 -0700)
commit944d671d5faa0d78980a3da5c0f04960ef1ad893
tree61215bceb853496d1e709ad7a4ad2658878d51f6
parent26821ecd3b489c11ecfbd3942bc7fef7629464b6
sch_htb: fix refcount leak in htb_parent_to_leaf_offload

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>
net/sched/sch_htb.c