[PATCH AUTOSEL 5.15 12/24] firewire: net: fix use after free in fwnet_finish_incoming_packet()

[Sasha Levin]

From: Zhang Shurong <zhang_shurong@xxxxxxxxxxx>

[ Upstream commit 3ff256751a2853e1ffaa36958ff933ccc98c6cb5 ]

The netif_rx() function frees the skb so we can't dereference it to
save the skb->len.

Signed-off-by: Zhang Shurong <zhang_shurong@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/tencent_3B3D24B66ED66A6BB73CC0E63C6A14E45109@xxxxxx
Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/firewire/net.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 4c3fd2eed1da4..beba0a56bb9ae 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -488,7 +488,7 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
 					struct sk_buff *skb, u16 source_node_id,
 					bool is_broadcast, u16 ether_type)
 {
-	int status;
+	int status, len;
 
 	switch (ether_type) {
 	case ETH_P_ARP:
@@ -542,13 +542,15 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
 		}
 		skb->protocol = protocol;
 	}
+
+	len = skb->len;
 	status = netif_rx(skb);
 	if (status == NET_RX_DROP) {
 		net->stats.rx_errors++;
 		net->stats.rx_dropped++;
 	} else {
 		net->stats.rx_packets++;
-		net->stats.rx_bytes += skb->len;
+		net->stats.rx_bytes += len;
 	}
 
 	return 0;
-- 
2.39.2