From a1775e4196ef2c67c4a89736d1d2687a49b881b5 Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Wed, 9 Oct 2024 11:43:42 -0500 Subject: [PATCH] sch/netem: fix use after free in netem_dequeue commit 3b3a2a9c6349e25a025d2330f479bc33a6ccb54a upstream. 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 Signed-off-by: Greg Kroah-Hartman (cherry picked from commit 32008ab989ddcff1a485fa2b4906234c25dc5cd6 linux-6.10.y) CVE-2024-46800 Signed-off-by: Bethany Jamison Acked-by: Ivan Hu Acked-by: Guoqing Jiang Signed-off-by: Roxana Nicolescu --- 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 0d29d0ccf8cb..f7d8c9063610 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -742,11 +742,10 @@ deliver: 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; }