udpencap: Remove Obsolete UDP_ENCAP_ESPINUDP_NON_IKE Support

The UDP_ENCAP_ESPINUDP_NON_IKE mode, introduced into the Linux kernel
in 2004 [2], has remained inactive and obsolete for an extended period.

This mode was originally defined in an early version of an IETF draft
[1] from 2001. By the time it was integrated into the kernel in 2004 [2],
it had already been replaced by UDP_ENCAP_ESPINUDP [3] in later
versions of draft-ietf-ipsec-udp-encaps, particularly in version 06.

Over time, UDP_ENCAP_ESPINUDP_NON_IKE has lost its relevance, with no
known use cases.

With this commit, we remove support for UDP_ENCAP_ESPINUDP_NON_IKE,
simplifying the codebase and eliminating unnecessary complexity.
Kernel will return an error -ENOPROTOOPT if the userspace tries to set
this option.

References:
[1] https://datatracker.ietf.org/doc/html/draft-ietf-ipsec-udp-encaps-00.txt

[2] Commit that added UDP_ENCAP_ESPINUDP_NON_IKE to the Linux historic
    repository.

    Author: Andreas Gruenbacher <agruen@suse.de>
    Date: Fri Apr 9 01:47:47 2004 -0700

   [IPSEC]: Support draft-ietf-ipsec-udp-encaps-00/01, some ipec impls need it.

[3] Commit that added UDP_ENCAP_ESPINUDP to the Linux historic
    repository.

    Author: Derek Atkins <derek@ihtfp.com>
    Date: Wed Apr 2 13:21:02 2003 -0800

    [IPSEC]: Implement UDP Encapsulation framework.
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/uapi/linux/udp.h

@@ -36,7 +36,7 @@ struct udphdr {
 #define UDP_GRO		104	/* This socket can receive UDP GRO packets */
 
 /* UDP encapsulation types */
-#define UDP_ENCAP_ESPINUDP_NON_IKE	1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
+#define UDP_ENCAP_ESPINUDP_NON_IKE	1 /* unused  draft-ietf-ipsec-nat-t-ike-00/01 */
 #define UDP_ENCAP_ESPINUDP	2 /* draft-ietf-ipsec-udp-encaps-06 */
 #define UDP_ENCAP_L2TPINUDP	3 /* rfc2661 */
 #define UDP_ENCAP_GTP0		4 /* GSM TS 09.60 */

net/ipv4/esp4.c

@@ -347,7 +347,6 @@ static struct ip_esp_hdr *esp_output_udp_encap(struct sk_buff *skb,
 					       __be16 dport)
 {
 	struct udphdr *uh;
-	__be32 *udpdata32;
 	unsigned int len;
 
 	len = skb->len + esp->tailen - skb_transport_offset(skb);
@@ -362,12 +361,6 @@ static struct ip_esp_hdr *esp_output_udp_encap(struct sk_buff *skb,
 
 	*skb_mac_header(skb) = IPPROTO_UDP;
 
-	if (encap_type == UDP_ENCAP_ESPINUDP_NON_IKE) {
-		udpdata32 = (__be32 *)(uh + 1);
-		udpdata32[0] = udpdata32[1] = 0;
-		return (struct ip_esp_hdr *)(udpdata32 + 2);
-	}
-
 	return (struct ip_esp_hdr *)(uh + 1);
 }
 
@@ -423,7 +416,6 @@ static int esp_output_encap(struct xfrm_state *x, struct sk_buff *skb,
 	switch (encap_type) {
 	default:
 	case UDP_ENCAP_ESPINUDP:
-	case UDP_ENCAP_ESPINUDP_NON_IKE:
 		esph = esp_output_udp_encap(skb, encap_type, esp, sport, dport);
 		break;
 	case TCP_ENCAP_ESPINTCP:
@@ -775,7 +767,6 @@ int esp_input_done2(struct sk_buff *skb, int err)
 			source = th->source;
 			break;
 		case UDP_ENCAP_ESPINUDP:
-		case UDP_ENCAP_ESPINUDP_NON_IKE:
 			source = uh->source;
 			break;
 		default:
@@ -1179,9 +1170,6 @@ static int esp_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
 		case UDP_ENCAP_ESPINUDP:
 			x->props.header_len += sizeof(struct udphdr);
 			break;
-		case UDP_ENCAP_ESPINUDP_NON_IKE:
-			x->props.header_len += sizeof(struct udphdr) + 2 * sizeof(u32);
-			break;
 #ifdef CONFIG_INET_ESPINTCP
 		case TCP_ENCAP_ESPINTCP:
 			/* only the length field, TCP encap is done by

net/ipv4/udp.c

@@ -2699,8 +2699,6 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 #ifdef CONFIG_XFRM
 		case UDP_ENCAP_ESPINUDP:
 			set_xfrm_gro_udp_encap_rcv(val, sk->sk_family, sk);
-			fallthrough;
-		case UDP_ENCAP_ESPINUDP_NON_IKE:
 #if IS_ENABLED(CONFIG_IPV6)
 			if (sk->sk_family == AF_INET6)
 				WRITE_ONCE(up->encap_rcv,

net/ipv4/xfrm4_input.c

@@ -113,19 +113,6 @@ static int __xfrm4_udp_encap_rcv(struct sock *sk, struct sk_buff *skb, bool pull
 			/* Must be an IKE packet.. pass it through */
 			return 1;
 		break;
-	case UDP_ENCAP_ESPINUDP_NON_IKE:
-		/* Check if this is a keepalive packet.  If so, eat it. */
-		if (len == 1 && udpdata[0] == 0xff) {
-			return -EINVAL;
-		} else if (len > 2 * sizeof(u32) + sizeof(struct ip_esp_hdr) &&
-			   udpdata32[0] == 0 && udpdata32[1] == 0) {
-
-			/* ESP Packet with Non-IKE marker */
-			len = sizeof(struct udphdr) + 2 * sizeof(u32);
-		} else
-			/* Must be an IKE packet.. pass it through */
-			return 1;
-		break;
 	}
 
 	/* At this point we are sure that this is an ESPinUDP packet,

net/ipv6/esp6.c

@@ -383,7 +383,6 @@ static struct ip_esp_hdr *esp6_output_udp_encap(struct sk_buff *skb,
 					       __be16 dport)
 {
 	struct udphdr *uh;
-	__be32 *udpdata32;
 	unsigned int len;
 
 	len = skb->len + esp->tailen - skb_transport_offset(skb);
@@ -398,12 +397,6 @@ static struct ip_esp_hdr *esp6_output_udp_encap(struct sk_buff *skb,
 
 	*skb_mac_header(skb) = IPPROTO_UDP;
 
-	if (encap_type == UDP_ENCAP_ESPINUDP_NON_IKE) {
-		udpdata32 = (__be32 *)(uh + 1);
-		udpdata32[0] = udpdata32[1] = 0;
-		return (struct ip_esp_hdr *)(udpdata32 + 2);
-	}
-
 	return (struct ip_esp_hdr *)(uh + 1);
 }
 
@@ -459,7 +452,6 @@ static int esp6_output_encap(struct xfrm_state *x, struct sk_buff *skb,
 	switch (encap_type) {
 	default:
 	case UDP_ENCAP_ESPINUDP:
-	case UDP_ENCAP_ESPINUDP_NON_IKE:
 		esph = esp6_output_udp_encap(skb, encap_type, esp, sport, dport);
 		break;
 	case TCP_ENCAP_ESPINTCP:
@@ -822,7 +814,6 @@ int esp6_input_done2(struct sk_buff *skb, int err)
 			source = th->source;
 			break;
 		case UDP_ENCAP_ESPINUDP:
-		case UDP_ENCAP_ESPINUDP_NON_IKE:
 			source = uh->source;
 			break;
 		default:
@@ -1232,9 +1223,6 @@ static int esp6_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
 		case UDP_ENCAP_ESPINUDP:
 			x->props.header_len += sizeof(struct udphdr);
 			break;
-		case UDP_ENCAP_ESPINUDP_NON_IKE:
-			x->props.header_len += sizeof(struct udphdr) + 2 * sizeof(u32);
-			break;
 #ifdef CONFIG_INET6_ESPINTCP
 		case TCP_ENCAP_ESPINTCP:
 			/* only the length field, TCP encap is done by

net/ipv6/xfrm6_input.c

@@ -109,19 +109,6 @@ static int __xfrm6_udp_encap_rcv(struct sock *sk, struct sk_buff *skb, bool pull
 			/* Must be an IKE packet.. pass it through */
 			return 1;
 		break;
-	case UDP_ENCAP_ESPINUDP_NON_IKE:
-		/* Check if this is a keepalive packet.  If so, eat it. */
-		if (len == 1 && udpdata[0] == 0xff) {
-			return -EINVAL;
-		} else if (len > 2 * sizeof(u32) + sizeof(struct ip_esp_hdr) &&
-			   udpdata32[0] == 0 && udpdata32[1] == 0) {
-
-			/* ESP Packet with Non-IKE marker */
-			len = sizeof(struct udphdr) + 2 * sizeof(u32);
-		} else
-			/* Must be an IKE packet.. pass it through */
-			return 1;
-		break;
 	}
 
 	/* At this point we are sure that this is an ESPinUDP packet,