From 3b3a2a9c6349e25a025d2330f479bc33a6ccb54a Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Sun, 1 Sep 2024 11:16:07 -0700 Subject: [PATCH] sch/netem: fix use after free in netem_dequeue If netem_dequeue() enqueues packet to inner qdisc and that qdisc returns __NET_XMIT_STOLEN. The packet is dropped but qdisc_tree_reduce_backlog() is not called to update the parent's q.qlen, leading to the similar use-after-free as Commit e04991a48dbaf382 ("netem: fix return value if duplicate enqueue fails") Commands to trigger KASAN UaF: ip link add type dummy ip link set lo up ip link set dummy0 up tc qdisc add dev lo parent root handle 1: drr tc filter add dev lo parent 1: basic classid 1:1 tc class add dev lo classid 1:1 drr tc qdisc add dev lo parent 1:1 handle 2: netem tc qdisc add dev lo parent 2: handle 3: drr tc filter add dev lo parent 3: basic classid 3:1 action mirred egress redirect dev dummy0 tc class add dev lo classid 3:1 drr ping -c1 -W0.01 localhost # Trigger bug tc class del dev lo classid 1:1 tc class add dev lo classid 1:1 drr ping -c1 -W0.01 localhost # UaF Fixes: 50612537e9ab ("netem: fix classful handling") Reported-by: Budimir Markovic Signed-off-by: Stephen Hemminger Link: https://patch.msgid.link/20240901182438.4992-1-stephen@networkplumber.org Signed-off-by: Jakub Kicinski --- net/sched/sch_netem.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 0f8d581438c3..39382ee1e331 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -742,11 +742,10 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch) err = qdisc_enqueue(skb, q->qdisc, &to_free); kfree_skb_list(to_free); - if (err != NET_XMIT_SUCCESS && - net_xmit_drop_count(err)) { - qdisc_qstats_drop(sch); - qdisc_tree_reduce_backlog(sch, 1, - pkt_len); + if (err != NET_XMIT_SUCCESS) { + if (net_xmit_drop_count(err)) + qdisc_qstats_drop(sch); + qdisc_tree_reduce_backlog(sch, 1, pkt_len); } goto tfifo_dequeue; }