ip: validate header length on virtual device xmit

KMSAN detected read beyond end of buffer in vti and sit devices when
passing truncated packets with PF_PACKET. The issue affects additional
ip tunnel devices.

Extend commit 76c0ddd8c3a6 ("ip6_tunnel: be careful when accessing the
inner header") and commit ccfec9e5cb2d ("ip_tunnel: be careful when
accessing the inner header").

Move the check to a separate helper and call at the start of each
ndo_start_xmit function in net/ipv4 and net/ipv6.

Minor changes:
- convert dev_kfree_skb to kfree_skb on error path,
  as dev_kfree_skb calls consume_skb which is not for error paths.
- use pskb_network_may_pull even though that is pedantic here,
  as the same as pskb_may_pull for devices without llheaders.
- do not cache ipv6 hdrs if used only once
  (unsafe across pskb_may_pull, was more relevant to earlier patch)

Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 18 insertions, 12 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index c7a7bd58a23c..d1d09f3e5f9e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -676,6 +676,9 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	const struct iphdr *tnl_params;
 
+	if (!pskb_inet_may_pull(skb))
+		goto free_skb;
+
 	if (tunnel->collect_md) {
 		gre_fb_xmit(skb, dev, skb->protocol);
 		return NETDEV_TX_OK;
@@ -719,6 +722,9 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	bool truncate = false;
 
+	if (!pskb_inet_may_pull(skb))
+		goto free_skb;
+
 	if (tunnel->collect_md) {
 		erspan_fb_xmit(skb, dev, skb->protocol);
 		return NETDEV_TX_OK;
@@ -762,6 +768,9 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff *skb,
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 
+	if (!pskb_inet_may_pull(skb))
+		goto free_skb;
+
 	if (tunnel->collect_md) {
 		gre_fb_xmit(skb, dev, htons(ETH_P_TEB));
 		return NETDEV_TX_OK;
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 284a22154b4e..c4f5602308ed 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -627,7 +627,6 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
 		    const struct iphdr *tnl_params, u8 protocol)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
-	unsigned int inner_nhdr_len = 0;
 	const struct iphdr *inner_iph;
 	struct flowi4 fl4;
 	u8     tos, ttl;
@@ -637,14 +636,6 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
 	__be32 dst;
 	bool connected;
 
-	/* ensure we can access the inner net header, for several users below */
-	if (skb->protocol == htons(ETH_P_IP))
-		inner_nhdr_len = sizeof(struct iphdr);
-	else if (skb->protocol == htons(ETH_P_IPV6))
-		inner_nhdr_len = sizeof(struct ipv6hdr);
-	if (unlikely(!pskb_may_pull(skb, inner_nhdr_len)))
-		goto tx_error;
-
 	inner_iph = (const struct iphdr *)skb_inner_network_header(skb);
 	connected = (tunnel->parms.iph.daddr != 0);
 
diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index de31b302d69c..d7b43e700023 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -241,6 +241,9 @@ static netdev_tx_t vti_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct flowi fl;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	memset(&fl, 0, sizeof(fl));
 
 	switch (skb->protocol) {
@@ -253,15 +256,18 @@ static netdev_tx_t vti_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 		memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
 		break;
 	default:
-		dev->stats.tx_errors++;
-		dev_kfree_skb(skb);
-		return NETDEV_TX_OK;
+		goto tx_err;
 	}
 
 	/* override mark with tunnel output key */
 	fl.flowi_mark = be32_to_cpu(tunnel->parms.o_key);
 
 	return vti_xmit(skb, dev, &fl);
+
+tx_err:
+	dev->stats.tx_errors++;
+	kfree_skb(skb);
+	return NETDEV_TX_OK;
 }
 
 static int vti4_err(struct sk_buff *skb, u32 info)