[PATCH 4.19 16/79] sch_cake: Return __NET_XMIT_STOLEN when consuming enqueued skb

[Greg Kroah-Hartman]

From: Toke Høiland-Jørgensen <toke@xxxxxxx>

[ Upstream commit 90fabae8a2c225c4e4936723c38857887edde5cc ]

When the GSO splitting feature of sch_cake is enabled, GSO superpackets
will be broken up and the resulting segments enqueued in place of the
original skb. In this case, CAKE calls consume_skb() on the original skb,
but still returns NET_XMIT_SUCCESS. This can confuse parent qdiscs into
assuming the original skb still exists, when it really has been freed. Fix
this by adding the __NET_XMIT_STOLEN flag to the return value in this case.

Fixes: 0c850344d388 ("sch_cake: Conditionally split GSO segments")
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxx>
Reported-by: zdi-disclosures@xxxxxxxxxxxxxx # ZDI-CAN-18231
Link: https://lore.kernel.org/r/20220831092103.442868-1-toke@xxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/sched/sch_cake.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 18c207b85d513..c0a6947545280 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1666,6 +1666,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	}
 	idx--;
 	flow = &b->flows[idx];
+	ret = NET_XMIT_SUCCESS;
 
 	/* ensure shaper state isn't stale */
 	if (!b->tin_backlog) {
@@ -1726,6 +1727,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 		qdisc_tree_reduce_backlog(sch, 1-numsegs, len-slen);
 		consume_skb(skb);
+		ret |= __NET_XMIT_STOLEN;
 	} else {
 		/* not splitting */
 		cobalt_set_enqueue_time(skb, now);
@@ -1849,7 +1851,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		}
 		b->drop_overlimit += dropped;
 	}
-	return NET_XMIT_SUCCESS;
+	return ret;
 }
 
 static struct sk_buff *cake_dequeue_one(struct Qdisc *sch)
-- 
2.35.1