// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * xfrm6_output.c - Common IPsec encapsulation code for IPv6.
 * Copyright (C) 2002 USAGI/WIDE Project
 * Copyright (c) 2004 Herbert Xu <herbert@gondor.apana.org.au>
 */

#include <linux/if_ether.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/icmpv6.h>
#include <linux/netfilter_ipv6.h>
#include <net/dst.h>
#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/xfrm.h>

void xfrm6_local_rxpmtu(struct sk_buff *skb, u32 mtu)
{
        struct flowi6 fl6;
        struct sock *sk = skb->sk;

        fl6.flowi6_oif = sk->sk_bound_dev_if;
        fl6.daddr = ipv6_hdr(skb)->daddr;

        ipv6_local_rxpmtu(sk, &fl6, mtu);
}

void xfrm6_local_error(struct sk_buff *skb, u32 mtu)
{
        struct flowi6 fl6;
        const struct ipv6hdr *hdr;
        struct sock *sk = skb->sk;

        hdr = skb->encapsulation ? inner_ipv6_hdr(skb) : ipv6_hdr(skb);
        fl6.fl6_dport = inet_sk(sk)->inet_dport;
        fl6.daddr = hdr->daddr;

        ipv6_local_error(sk, EMSGSIZE, &fl6, mtu);
}

static int __xfrm6_output_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        return xfrm_output(sk, skb);
}

static int xfrm6_noneed_fragment(struct sk_buff *skb)
{
        struct frag_hdr *fh;
        u8 prevhdr = ipv6_hdr(skb)->nexthdr;

        if (prevhdr != NEXTHDR_FRAGMENT)
                return 0;
        fh = (struct frag_hdr *)(skb->data + sizeof(struct ipv6hdr));
        if (fh->nexthdr == NEXTHDR_ESP || fh->nexthdr == NEXTHDR_AUTH)
                return 1;
        return 0;
}

static int __xfrm6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);
        struct xfrm_state *x = dst->xfrm;
        unsigned int mtu;
        bool toobig;

#ifdef CONFIG_NETFILTER
        if (!x) {
                IP6CB(skb)->flags |= IP6SKB_REROUTED;
                return dst_output(net, sk, skb);
        }
#endif

        if (x->props.mode != XFRM_MODE_TUNNEL)
                goto skip_frag;

        if (skb->protocol == htons(ETH_P_IPV6))
                mtu = ip6_skb_dst_mtu(skb);
        else
                mtu = dst_mtu(skb_dst(skb));

        toobig = skb->len > mtu && !skb_is_gso(skb);

        if (toobig && xfrm6_local_dontfrag(sk)) {
                xfrm6_local_rxpmtu(skb, mtu);
                kfree_skb(skb);
                return -EMSGSIZE;
        } else if (toobig && xfrm6_noneed_fragment(skb)) {
                skb->ignore_df = 1;
                goto skip_frag;
        } else if (!skb->ignore_df && toobig && sk) {
                xfrm_local_error(skb, mtu);
                kfree_skb(skb);
                return -EMSGSIZE;
        }

        if (toobig)
                return ip6_fragment(net, sk, skb,
                                    __xfrm6_output_finish);

skip_frag:
        return xfrm_output(sk, skb);
}

int xfrm6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        return NF_HOOK_COND(NFPROTO_IPV6, NF_INET_POST_ROUTING,
                            net, sk, skb,  skb->dev, skb_dst_dev(skb),
                            __xfrm6_output,
                            !(IP6CB(skb)->flags & IP6SKB_REROUTED));
}