vti6: fix input path

Since commit 1625f4529957, vti6 is broken, all input packets are dropped
(LINUX_MIB_XFRMINNOSTATES is incremented).

XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 is set by vti6_rcv() before calling
xfrm6_rcv()/xfrm6_rcv_spi(), thus we cannot set to NULL that value in
xfrm6_rcv_spi().

A new function xfrm6_rcv_tnl() that enables to pass a value to
xfrm6_rcv_spi() is added, so that xfrm6_rcv() is not touched (this function
is used in several handlers).

CC: Alexey Kodanev <alexey.kodanev@oracle.com>
Fixes: 1625f4529957 ("net/xfrm_input: fix possible NULL deref of tunnel.ip6->parms.i_key")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 00a2d40..b578956 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -21,9 +21,10 @@
 	return xfrm6_extract_header(skb);
 }
 
-int xfrm6_rcv_spi(struct sk_buff *skb, int nexthdr, __be32 spi)
+int xfrm6_rcv_spi(struct sk_buff *skb, int nexthdr, __be32 spi,
+		  struct ip6_tnl *t)
 {
-	XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 = NULL;
+	XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 = t;
 	XFRM_SPI_SKB_CB(skb)->family = AF_INET6;
 	XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct ipv6hdr, daddr);
 	return xfrm_input(skb, nexthdr, spi, 0);
@@ -49,13 +50,18 @@
 	return -1;
 }
 
-int xfrm6_rcv(struct sk_buff *skb)
+int xfrm6_rcv_tnl(struct sk_buff *skb, struct ip6_tnl *t)
 {
 	return xfrm6_rcv_spi(skb, skb_network_header(skb)[IP6CB(skb)->nhoff],
-			     0);
+			     0, t);
+}
+EXPORT_SYMBOL(xfrm6_rcv_tnl);
+
+int xfrm6_rcv(struct sk_buff *skb)
+{
+	return xfrm6_rcv_tnl(skb, NULL);
 }
 EXPORT_SYMBOL(xfrm6_rcv);
-
 int xfrm6_input_addr(struct sk_buff *skb, xfrm_address_t *daddr,
 		     xfrm_address_t *saddr, u8 proto)
 {