netdev - [PATCH net] net: sched: Fix use after free in red

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Date:   Fri, 28 Oct 2022 18:05:00 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Subject: [PATCH net] net: sched: Fix use after free in red_enqueue()

We can't use "skb" again after passing it to qdisc_enqueue().  This is
basically identical to commit 2f09707d0c97 ("sch_sfb: Also store skb
len before calling child enqueue").

Fixes: d7f4f332f082 ("sch_red: update backlog as well")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
Applies to net.

 net/sched/sch_red.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c
index a5a401f93c1a..98129324e157 100644
--- a/net/sched/sch_red.c
+++ b/net/sched/sch_red.c
@@ -72,6 +72,7 @@ static int red_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 {
 	struct red_sched_data *q = qdisc_priv(sch);
 	struct Qdisc *child = q->qdisc;
+	unsigned int len;
 	int ret;
 
 	q->vars.qavg = red_calc_qavg(&q->parms,
@@ -126,9 +127,10 @@ static int red_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		break;
 	}
 
+	len = qdisc_pkt_len(skb);
 	ret = qdisc_enqueue(skb, child, to_free);
 	if (likely(ret == NET_XMIT_SUCCESS)) {
-		qdisc_qstats_backlog_inc(sch, skb);
+		sch->qstats.backlog += len;
 		sch->q.qlen++;
 	} else if (net_xmit_drop_count(ret)) {
 		q->stats.pdrop++;
-- 
2.35.1