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 76c0ddd8 ("ip6_tunnel: be careful when accessing the
inner header") and commit ccfec9e5 ("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>

include/net/ip_tunnels.h

@@ -308,6 +308,26 @@ int ip_tunnel_encap_del_ops(const struct ip_tunnel_encap_ops *op,
 int ip_tunnel_encap_setup(struct ip_tunnel *t,
 			  struct ip_tunnel_encap *ipencap);
 
+static inline bool pskb_inet_may_pull(struct sk_buff *skb)
+{
+	int nhlen;
+
+	switch (skb->protocol) {
+#if IS_ENABLED(CONFIG_IPV6)
+	case htons(ETH_P_IPV6):
+		nhlen = sizeof(struct ipv6hdr);
+		break;
+#endif
+	case htons(ETH_P_IP):
+		nhlen = sizeof(struct iphdr);
+		break;
+	default:
+		nhlen = 0;
+	}
+
+	return pskb_network_may_pull(skb, nhlen);
+}
+
 static inline int ip_encap_hlen(struct ip_tunnel_encap *e)
 {
 	const struct ip_tunnel_encap_ops *ops;

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;

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);
 

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)

net/ipv6/ip6_gre.c

@@ -881,6 +881,9 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff *skb,
 	struct net_device_stats *stats = &t->dev->stats;
 	int ret;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	if (!ip6_tnl_xmit_ctl(t, &t->parms.laddr, &t->parms.raddr))
 		goto tx_err;
 
@@ -923,6 +926,9 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 	int nhoff;
 	int thoff;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	if (!ip6_tnl_xmit_ctl(t, &t->parms.laddr, &t->parms.raddr))
 		goto tx_err;
 
@@ -995,8 +1001,6 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 			goto tx_err;
 		}
 	} else {
-		struct ipv6hdr *ipv6h = ipv6_hdr(skb);
-
 		switch (skb->protocol) {
 		case htons(ETH_P_IP):
 			memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
@@ -1004,7 +1008,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 						 &dsfield, &encap_limit);
 			break;
 		case htons(ETH_P_IPV6):
-			if (ipv6_addr_equal(&t->parms.raddr, &ipv6h->saddr))
+			if (ipv6_addr_equal(&t->parms.raddr, &ipv6_hdr(skb)->saddr))
 				goto tx_err;
 			if (prepare_ip6gre_xmit_ipv6(skb, dev, &fl6,
 						     &dsfield, &encap_limit))

net/ipv6/ip6_tunnel.c

@@ -1243,10 +1243,6 @@ ip4ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 	u8 tproto;
 	int err;
 
-	/* ensure we can access the full inner ip header */
-	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
-		return -1;
-
 	iph = ip_hdr(skb);
 	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 
@@ -1321,9 +1317,6 @@ ip6ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 	u8 tproto;
 	int err;
 
-	if (unlikely(!pskb_may_pull(skb, sizeof(*ipv6h))))
-		return -1;
-
 	ipv6h = ipv6_hdr(skb);
 	tproto = READ_ONCE(t->parms.proto);
 	if ((tproto != IPPROTO_IPV6 && tproto != 0) ||
@@ -1405,6 +1398,9 @@ ip6_tnl_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct net_device_stats *stats = &t->dev->stats;
 	int ret;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		ret = ip4ip6_tnl_xmit(skb, dev);

net/ipv6/ip6_vti.c

@@ -522,18 +522,18 @@ vti6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ip6_tnl *t = netdev_priv(dev);
 	struct net_device_stats *stats = &t->dev->stats;
-	struct ipv6hdr *ipv6h;
 	struct flowi fl;
 	int ret;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	memset(&fl, 0, sizeof(fl));
 
 	switch (skb->protocol) {
 	case htons(ETH_P_IPV6):
-		ipv6h = ipv6_hdr(skb);
-
 		if ((t->parms.proto != IPPROTO_IPV6 && t->parms.proto != 0) ||
-		    vti6_addr_conflict(t, ipv6h))
+		    vti6_addr_conflict(t, ipv6_hdr(skb)))
 			goto tx_err;
 
 		xfrm_decode_session(skb, &fl, AF_INET6);

net/ipv6/ip6mr.c

@@ -51,6 +51,7 @@
 #include <linux/export.h>
 #include <net/ip6_checksum.h>
 #include <linux/netconf.h>
+#include <net/ip_tunnels.h>
 
 #include <linux/nospec.h>
 
@@ -599,13 +600,12 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb,
 		.flowi6_iif	= skb->skb_iif ? : LOOPBACK_IFINDEX,
 		.flowi6_mark	= skb->mark,
 	};
-	int err;
 
-	err = ip6mr_fib_lookup(net, &fl6, &mrt);
-	if (err < 0) {
-		kfree_skb(skb);
-		return err;
-	}
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
+	if (ip6mr_fib_lookup(net, &fl6, &mrt) < 0)
+		goto tx_err;
 
 	read_lock(&mrt_lock);
 	dev->stats.tx_bytes += skb->len;
@@ -614,6 +614,11 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb,
 	read_unlock(&mrt_lock);
 	kfree_skb(skb);
 	return NETDEV_TX_OK;
+
+tx_err:
+	dev->stats.tx_errors++;
+	kfree_skb(skb);
+	return NETDEV_TX_OK;
 }
 
 static int reg_vif_get_iflink(const struct net_device *dev)

net/ipv6/sit.c

@@ -1021,6 +1021,9 @@ static netdev_tx_t sit_tunnel_xmit__(struct sk_buff *skb,
 static netdev_tx_t sit_tunnel_xmit(struct sk_buff *skb,
 				   struct net_device *dev)
 {
+	if (!pskb_inet_may_pull(skb))
+		goto tx_err;
+
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		sit_tunnel_xmit__(skb, dev, IPPROTO_IPIP);