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>

5 files changed, 28 insertions, 20 deletions

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 229e55c99021..09d0826742f8 100644
--- a/net/ipv6/ip6_gre.c
+++ b/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))
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 99179b9c8384..0c6403cf8b52 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/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);
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 706fe42e4928..8b6eefff2f7e 100644
--- a/net/ipv6/ip6_vti.c
+++ b/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);
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 8276f1224f16..30337b38274b 100644
--- a/net/ipv6/ip6mr.c
+++ b/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)
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 51c9f75f34b9..1e03305c0549 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1021,6 +1021,9 @@ tx_error:
 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);