netdev - [PATCH net 3/3] ip_vti: fix potential slab-use-after-free in decode

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Date: Mon, 10 Jul 2023 17:40:53 +0800
From: Zhengchao Shao <shaozhengchao@...wei.com>
To: <netdev@...r.kernel.org>, <steffen.klassert@...unet.com>,
	<herbert@...dor.apana.org.au>, <davem@...emloft.net>, <dsahern@...nel.org>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>
CC: <weiyongjun1@...wei.com>, <yuehaibing@...wei.com>,
	<shaozhengchao@...wei.com>
Subject: [PATCH net 3/3] ip_vti: fix potential slab-use-after-free in decode_session6

When ip_vti device is set to the qdisc of the sfb type, the cb field
of the sent skb may be modified during enqueuing. Then,
slab-use-after-free may occur when ip_vti device sends IPv6 packets.
As commit f855691975bb ("xfrm6: Fix the nexthdr offset in
_decode_session6.") showed, xfrm_decode_session was originally intended
only for the receive path. IP6CB(skb)->nhoff is not set during
transmission. Therefore, set the cb field in the skb to 0 before
sending packets.

Fixes: f855691975bb ("xfrm6: Fix the nexthdr offset in _decode_session6.")
Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
---
 net/ipv4/ip_vti.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 53bfd8af6920..d1e7d0ceb7ed 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -287,12 +287,12 @@ static netdev_tx_t vti_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
-		xfrm_decode_session(skb, &fl, AF_INET);
 		memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
+		xfrm_decode_session(skb, &fl, AF_INET);
 		break;
 	case htons(ETH_P_IPV6):
-		xfrm_decode_session(skb, &fl, AF_INET6);
 		memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+		xfrm_decode_session(skb, &fl, AF_INET6);
 		break;
 	default:
 		goto tx_err;
-- 
2.34.1