// SPDX-License-Identifier: GPL-2.0
/*
 * xfrm4_input.c
 *
 * Changes:
 *      YOSHIFUJI Hideaki @USAGI
 *              Split up af-specific portion
 *      Derek Atkins <derek@ihtfp.com>
 *              Add Encapsulation support
 *
 */

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <net/ip.h>
#include <net/xfrm.h>
#include <net/protocol.h>
#include <net/gro.h>

static int xfrm4_rcv_encap_finish2(struct net *net, struct sock *sk,
                                   struct sk_buff *skb)
{
        return dst_input(skb);
}

static inline int xfrm4_rcv_encap_finish(struct net *net, struct sock *sk,
                                         struct sk_buff *skb)
{
        if (!skb_dst(skb)) {
                const struct iphdr *iph = ip_hdr(skb);

                if (ip_route_input_noref(skb, iph->daddr, iph->saddr,
                                         ip4h_dscp(iph), skb->dev))
                        goto drop;
        }

        if (xfrm_trans_queue(skb, xfrm4_rcv_encap_finish2))
                goto drop;

        return 0;
drop:
        kfree_skb(skb);
        return NET_RX_DROP;
}

int xfrm4_transport_finish(struct sk_buff *skb, int async)
{
        struct xfrm_offload *xo = xfrm_offload(skb);
        struct iphdr *iph = ip_hdr(skb);

        iph->protocol = XFRM_MODE_SKB_CB(skb)->protocol;

#ifndef CONFIG_NETFILTER
        if (!async)
                return -iph->protocol;
#endif

        __skb_push(skb, -skb_network_offset(skb));
        iph->tot_len = htons(skb->len);
        ip_send_check(iph);

        if (xo && (xo->flags & XFRM_GRO)) {
                /* The full l2 header needs to be preserved so that re-injecting the packet at l2
                 * works correctly in the presence of vlan tags.
                 */
                skb_mac_header_rebuild_full(skb, xo->orig_mac_len);
                skb_reset_network_header(skb);
                skb_reset_transport_header(skb);
                return 0;
        }

        NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
                dev_net(skb->dev), NULL, skb, skb->dev, NULL,
                xfrm4_rcv_encap_finish);
        return 0;
}

static int __xfrm4_udp_encap_rcv(struct sock *sk, struct sk_buff *skb, bool pull)
{
        struct udp_sock *up = udp_sk(sk);
        struct udphdr *uh;
        struct iphdr *iph;
        int iphlen, len;
        __u8 *udpdata;
        __be32 *udpdata32;
        u16 encap_type;

        encap_type = READ_ONCE(up->encap_type);
        /* if this is not encapsulated socket, then just return now */
        if (!encap_type)
                return 1;

        /* If this is a paged skb, make sure we pull up
         * whatever data we need to look at. */
        len = skb->len - sizeof(struct udphdr);
        if (!pskb_may_pull(skb, sizeof(struct udphdr) + min(len, 8)))
                return 1;

        /* Now we can get the pointers */
        uh = udp_hdr(skb);
        udpdata = (__u8 *)uh + sizeof(struct udphdr);
        udpdata32 = (__be32 *)udpdata;

        switch (encap_type) {
        default:
        case UDP_ENCAP_ESPINUDP:
                /* Check if this is a keepalive packet.  If so, eat it. */
                if (len == 1 && udpdata[0] == 0xff) {
                        return -EINVAL;
                } else if (len > sizeof(struct ip_esp_hdr) && udpdata32[0] != 0) {
                        /* ESP Packet without Non-ESP header */
                        len = sizeof(struct udphdr);
                } else
                        /* Must be an IKE packet.. pass it through */
                        return 1;
                break;
        }

        /* At this point we are sure that this is an ESPinUDP packet,
         * so we need to remove 'len' bytes from the packet (the UDP
         * header and optional ESP marker bytes) and then modify the
         * protocol to ESP, and then call into the transform receiver.
         */
        if (skb_unclone(skb, GFP_ATOMIC))
                return -EINVAL;

        /* Now we can update and verify the packet length... */
        iph = ip_hdr(skb);
        iphlen = iph->ihl << 2;
        iph->tot_len = htons(ntohs(iph->tot_len) - len);
        if (skb->len < iphlen + len) {
                /* packet is too small!?! */
                return -EINVAL;
        }

        /* pull the data buffer up to the ESP header and set the
         * transport header to point to ESP.  Keep UDP on the stack
         * for later.
         */
        if (pull) {
                __skb_pull(skb, len);
                skb_reset_transport_header(skb);
        } else {
                skb_set_transport_header(skb, len);
        }

        /* process ESP */
        return 0;
}

/* If it's a keepalive packet, then just eat it.
 * If it's an encapsulated packet, then pass it to the
 * IPsec xfrm input.
 * Returns 0 if skb passed to xfrm or was dropped.
 * Returns >0 if skb should be passed to UDP.
 * Returns <0 if skb should be resubmitted (-ret is protocol)
 */
int xfrm4_udp_encap_rcv(struct sock *sk, struct sk_buff *skb)
{
        int ret;

        ret = __xfrm4_udp_encap_rcv(sk, skb, true);
        if (!ret)
                return xfrm4_rcv_encap(skb, IPPROTO_ESP, 0,
                                       udp_sk(sk)->encap_type);

        if (ret < 0) {
                kfree_skb(skb);
                return 0;
        }

        return ret;
}
EXPORT_SYMBOL(xfrm4_udp_encap_rcv);

struct sk_buff *xfrm4_gro_udp_encap_rcv(struct sock *sk, struct list_head *head,
                                        struct sk_buff *skb)
{
        int offset = skb_gro_offset(skb);
        const struct net_offload *ops;
        struct sk_buff *pp = NULL;
        int len, dlen;
        __u8 *udpdata;
        __be32 *udpdata32;

        len = skb->len - offset;
        dlen = offset + min(len, 8);
        udpdata = skb_gro_header(skb, dlen, offset);
        udpdata32 = (__be32 *)udpdata;
        if (unlikely(!udpdata))
                return NULL;

        rcu_read_lock();
        ops = rcu_dereference(inet_offloads[IPPROTO_ESP]);
        if (!ops || !ops->callbacks.gro_receive)
                goto out;

        /* check if it is a keepalive or IKE packet */
        if (len <= sizeof(struct ip_esp_hdr) || udpdata32[0] == 0)
                goto out;

        /* set the transport header to ESP */
        skb_set_transport_header(skb, offset);

        NAPI_GRO_CB(skb)->proto = IPPROTO_UDP;

        pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
        rcu_read_unlock();

        return pp;

out:
        rcu_read_unlock();
        NAPI_GRO_CB(skb)->same_flow = 0;
        NAPI_GRO_CB(skb)->flush = 1;

        return NULL;
}
EXPORT_SYMBOL(xfrm4_gro_udp_encap_rcv);

int xfrm4_rcv(struct sk_buff *skb)
{
        return xfrm4_rcv_spi(skb, ip_hdr(skb)->protocol, 0);
}
EXPORT_SYMBOL(xfrm4_rcv);