[SRU OEM-5.14, OEM-5.17 1/1] net: sched: Fix use after free in red_enqueue()

[Cengiz Can]

From: Dan Carpenter <dan.carpenter at oracle.com>

BugLink: https://bugs.launchpad.net/bugs/2017013

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 at oracle.com>
Reviewed-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 8bdc2acd420c6f3dd1f1c78750ec989f02a1e2b9)
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 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 40adf1f07a82..b310842b4225 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++;
-- 
2.37.2