netdev - [PATCH net-next] netdevsim: fix UaF when counting Tx stats

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Message-ID: <20250620174007.2188470-1-kuba@kernel.org>
Date: Fri, 20 Jun 2025 10:40:07 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org,
	edumazet@...gle.com,
	pabeni@...hat.com,
	andrew+netdev@...n.ch,
	horms@...nel.org,
	Jakub Kicinski <kuba@...nel.org>,
	leitao@...ian.org,
	joe@...a.to
Subject: [PATCH net-next] netdevsim: fix UaF when counting Tx stats

skb may be freed as soon as we put it on the rx queue.
Use the len variable like the code did prior to the conversion.

Fixes: f9e2511d80c2 ("netdevsim: migrate to dstats stats collection")
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
CC: leitao@...ian.org
CC: joe@...a.to
---
 drivers/net/netdevsim/netdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 7f2809be5d48..e36d3e846c2d 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -93,7 +93,7 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		hrtimer_start(&rq->napi_timer, us_to_ktime(5), HRTIMER_MODE_REL);
 
 	rcu_read_unlock();
-	dev_dstats_tx_add(dev, skb->len);
+	dev_dstats_tx_add(dev, len);
 	return NETDEV_TX_OK;
 
 out_drop_free:
-- 
2.49.0