5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
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 <markovicbudimir@xxxxxxxxx>
Signed-off-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20240901182438.4992-1-stephen@xxxxxxxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/sched/sch_netem.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -733,11 +733,10 @@ 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;
}
