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Message-ID: <511c74b6-7d60-b60b-3f45-577c627fcf89@mitchellaugustin.com>
Date: Mon, 7 Aug 2023 17:59:54 -0500
From: Mitchell Augustin <mitchell@...chellaugustin.com>
To: Jamal Hadi Salim <jhs@...atatu.com>,
Cong Wang <xiyou.wangcong@...il.com>,
Jiri Pirko <jiri@...nulli.us>,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 4.19.289] net/sched: sch_qfq: account for stab overhead in
qfq_enqueue
From cb3f87086b7d412df344f120ecd324412103c903 Mon Aug 7 17:57:04 2023
From: Mitchell Augustin <mitchell@...chellaugustin.com>
Date: Mon, 7 Aug 2023 17:57:04 -0500
Subject: [PATCH 4.19.289] net/sched: sch_qfq: account for stab overhead
in qfq_enqueue
[ Upstream commit 3e337087c3b5805fe0b8a46ba622a962880b5d64 ]
I'm backporting the following patch from the mainline 6.5-rc4 branch
(the above commit) to the 4.19.289 tree.
Lion says:
-------
In the QFQ scheduler a similar issue to CVE-2023-31436
persists.
Consider the following code in net/sched/sch_qfq.c:
static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
unsigned int len = qdisc_pkt_len(skb), gso_segs;
// ...
if (unlikely(cl->agg->lmax < len)) {
pr_debug("qfq: increasing maxpkt from %u to %u for class %u",
cl->agg->lmax, len, cl->common.classid);
err = qfq_change_agg(sch, cl, cl->agg->class_weight, len);
if (err) {
cl->qstats.drops++;
return qdisc_drop(skb, sch, to_free);
}
// ...
}
Similarly to CVE-2023-31436, "lmax" is increased without any bounds
checks according to the packet length "len". Usually this would not
impose a problem because packet sizes are naturally limited.
This is however not the actual packet length, rather the
"qdisc_pkt_len(skb)" which might apply size transformations according to
"struct qdisc_size_table" as created by "qdisc_get_stab()" in
net/sched/sch_api.c if the TCA_STAB option was set when modifying the
qdisc.
A user may choose virtually any size using such a table.
As a result the same issue as in CVE-2023-31436 can occur, allowing heap
out-of-bounds read / writes in the kmalloc-8192 cache.
-------
We can create the issue with the following commands:
tc qdisc add dev $DEV root handle 1: stab mtu 2048 tsize 512 mpu 0 \
overhead 999999999 linklayer ethernet qfq
tc class add dev $DEV parent 1: classid 1:1 htb rate 6mbit burst 15k
tc filter add dev $DEV parent 1: matchall classid 1:1
ping -I $DEV 1.1.1.2
This is caused by incorrectly assuming that qdisc_pkt_len() returns a
length within the QFQ_MIN_LMAX < len < QFQ_MAX_LMAX.
---
net/sched/sch_qfq.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index c2a68f6e427e..81ebe7741463 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -116,6 +116,7 @@
#define QFQ_MTU_SHIFT 16 /* to support TSO/GSO */
#define QFQ_MIN_LMAX 512 /* see qfq_slot_insert */
+#define QFQ_MAX_LMAX (1UL << QFQ_MTU_SHIFT)
#define QFQ_MAX_AGG_CLASSES 8 /* max num classes per aggregate
allowed */
@@ -387,8 +388,13 @@ static int qfq_change_agg(struct Qdisc *sch, struct
qfq_class *cl, u32 weight,
u32 lmax)
{
struct qfq_sched *q = qdisc_priv(sch);
- struct qfq_aggregate *new_agg = qfq_find_agg(q, lmax, weight);
+ struct qfq_aggregate *new_agg;
+ /* 'lmax' can range from [QFQ_MIN_LMAX, pktlen + stab overhead] */
+ if (lmax > QFQ_MAX_LMAX)
+ return -EINVAL;
+
+ new_agg = qfq_find_agg(q, lmax, weight);
if (new_agg == NULL) { /* create new aggregate */
new_agg = kzalloc(sizeof(*new_agg), GFP_ATOMIC);
if (new_agg == NULL)
--
2.34.1
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