From: Stephen Hemminger stephen@networkplumber.org

stable inclusion from stable-v4.19.322 commit f0bddb4de043399f16d1969dad5ee5b984a64e7b category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IARX29 CVE: CVE-2024-46800

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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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@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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Wang Liang wangliang74@huawei.com --- 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 95832934e965..8e33bcd69edd 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -697,11 +697,10 @@ 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; }