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>

1 files changed, 4 insertions, 4 deletions

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);