netdev - [PATCH v1 net 5/5] ip6_tunnel: Pull header after checking skb->protocol in ip6_tnl_start

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Message-ID: <20240415222041.18537-6-kuniyu@amazon.com>
Date: Mon, 15 Apr 2024 15:20:41 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, David Ahern <dsahern@...nel.org>
CC: Steffen Klassert <steffen.klassert@...unet.com>, Herbert Xu
	<herbert@...dor.apana.org.au>, Willem de Bruijn <willemb@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...zon.com>, Kuniyuki Iwashima
	<kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v1 net 5/5] ip6_tunnel: Pull header after checking skb->protocol in ip6_tnl_start_xmit().

syzkaller demonstrated the underflow in pskb_network_may_pull()
by sending a crafted VLAN packet over tunnel devices: sit, ipip,
vti, and vti6.

The same warning will be triggered for ip6tnl, so let's check
skb->protocol before pulling the next header in ip6_tnl_start_xmit().

Fixes: cb9f1b783850 ("ip: validate header length on virtual device xmit")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv6/ip6_tunnel.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index e9cc315832cb..81be7a5be6c5 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1424,14 +1424,17 @@ ip6_tnl_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	u8 ipproto;
 	int ret;
 
-	if (!pskb_inet_may_pull(skb))
-		goto tx_err;
-
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
+		if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
+			goto tx_err;
+
 		ipproto = IPPROTO_IPIP;
 		break;
 	case htons(ETH_P_IPV6):
+		if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
+			goto tx_err;
+
 		if (ip6_tnl_addr_conflict(t, ipv6_hdr(skb)))
 			goto tx_err;
 		ipproto = IPPROTO_IPV6;
-- 
2.30.2