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sch/netem: fix use after free in netem_dequeue

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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: 50612537e9 ("netem: fix classful handling")
Reported-by: Budimir Markovic <markovicbudimir@gmail.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Link: https://patch.msgid.link/20240901182438.4992-1-stephen@networkplumber.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Stephen Hemminger 2024-09-01 11:16:07 -07:00 committed by Jakub Kicinski
parent bab8eb0dd4
commit 3b3a2a9c63
1 changed files with 4 additions and 5 deletions
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7
net/sched/sch_netem.c
View file

@ -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)) {
if (err != NET_XMIT_SUCCESS) {
if (net_xmit_drop_count(err))
qdisc_qstats_drop(sch);
qdisc_tree_reduce_backlog(sch, 1,
pkt_len);
qdisc_tree_reduce_backlog(sch, 1, pkt_len);
}
goto tfifo_dequeue;
}