Revert "Fix XFRM-I support for nested ESP tunnels"

This reverts commit b0355db.

The reverted commit clears the secpath on packets received via xfrm interfaces
to support nested IPsec tunnels. This breaks Netfilter policy matching using
xt_policy in the FORWARD chain, as the secpath is missing during forwarding.
Additionally, Benedict Wong reports that it breaks Transport-in-Tunnel mode.

Fix this regression by reverting the commit until we have a better approach
for nested IPsec tunnels.

Fixes: b0355db ("Fix XFRM-I support for nested ESP tunnels")
Link: https://lore.kernel.org/netdev/20230412085615.124791-1-martin@strongswan.org/
Signed-off-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: martinwilli

net/xfrm/xfrm_interface_core.c

@@ -310,52 +310,6 @@ static void xfrmi_scrub_packet(struct sk_buff *skb, bool xnet)
 	skb->mark = 0;
 }
 
-static int xfrmi_input(struct sk_buff *skb, int nexthdr, __be32 spi,
-		       int encap_type, unsigned short family)
-{
-	struct sec_path *sp;
-
-	sp = skb_sec_path(skb);
-	if (sp && (sp->len || sp->olen) &&
-	    !xfrm_policy_check(NULL, XFRM_POLICY_IN, skb, family))
-		goto discard;
-
-	XFRM_SPI_SKB_CB(skb)->family = family;
-	if (family == AF_INET) {
-		XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct iphdr, daddr);
-		XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4 = NULL;
-	} else {
-		XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct ipv6hdr, daddr);
-		XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 = NULL;
-	}
-
-	return xfrm_input(skb, nexthdr, spi, encap_type);
-discard:
-	kfree_skb(skb);
-	return 0;
-}
-
-static int xfrmi4_rcv(struct sk_buff *skb)
-{
-	return xfrmi_input(skb, ip_hdr(skb)->protocol, 0, 0, AF_INET);
-}
-
-static int xfrmi6_rcv(struct sk_buff *skb)
-{
-	return xfrmi_input(skb, skb_network_header(skb)[IP6CB(skb)->nhoff],
-			   0, 0, AF_INET6);
-}
-
-static int xfrmi4_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
-{
-	return xfrmi_input(skb, nexthdr, spi, encap_type, AF_INET);
-}
-
-static int xfrmi6_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
-{
-	return xfrmi_input(skb, nexthdr, spi, encap_type, AF_INET6);
-}
-
 static int xfrmi_rcv_cb(struct sk_buff *skb, int err)
 {
 	const struct xfrm_mode *inner_mode;
@@ -991,8 +945,8 @@ static struct pernet_operations xfrmi_net_ops = {
 };
 
 static struct xfrm6_protocol xfrmi_esp6_protocol __read_mostly = {
-	.handler	=	xfrmi6_rcv,
-	.input_handler	=	xfrmi6_input,
+	.handler	=	xfrm6_rcv,
+	.input_handler	=	xfrm_input,
 	.cb_handler	=	xfrmi_rcv_cb,
 	.err_handler	=	xfrmi6_err,
 	.priority	=	10,
@@ -1042,8 +996,8 @@ static struct xfrm6_tunnel xfrmi_ip6ip_handler __read_mostly = {
 #endif
 
 static struct xfrm4_protocol xfrmi_esp4_protocol __read_mostly = {
-	.handler	=	xfrmi4_rcv,
-	.input_handler	=	xfrmi4_input,
+	.handler	=	xfrm4_rcv,
+	.input_handler	=	xfrm_input,
 	.cb_handler	=	xfrmi_rcv_cb,
 	.err_handler	=	xfrmi4_err,
 	.priority	=	10,

net/xfrm/xfrm_policy.c

@@ -3739,9 +3739,6 @@ int __xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb,
 			goto reject;
 		}
 
-		if (if_id)
-			secpath_reset(skb);
-
 		xfrm_pols_put(pols, npols);
 		return 1;
 	}