// SPDX-License-Identifier: GPL-2.0-only
/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
 */

#include <linux/module.h>
#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/ip6_fib.h>
#include <net/ip6_checksum.h>
#include <net/netfilter/ipv6/nf_reject.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_bridge.h>

static struct ipv6hdr *
nf_reject_ip6hdr_put(struct sk_buff *nskb,
                     const struct sk_buff *oldskb,
                     __u8 protocol, int hoplimit);
static void
nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
                         const struct sk_buff *oldskb,
                         const struct tcphdr *oth, unsigned int otcplen);
static const struct tcphdr *
nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
                         struct tcphdr *otcph,
                         unsigned int *otcplen, int hook);

static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
{
        const struct ipv6hdr *ip6h = ipv6_hdr(skb);
        int thoff;
        __be16 fo;
        u8 proto = ip6h->nexthdr;

        if (skb_csum_unnecessary(skb))
                return true;

        if (ip6h->payload_len &&
            pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
                return false;

        ip6h = ipv6_hdr(skb);
        thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
        if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
                return false;

        if (!nf_reject_verify_csum(skb, thoff, proto))
                return true;

        return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
}

static int nf_reject_ip6hdr_validate(struct sk_buff *skb)
{
        struct ipv6hdr *hdr;
        u32 pkt_len;

        if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
                return 0;

        hdr = ipv6_hdr(skb);
        if (hdr->version != 6)
                return 0;

        pkt_len = ntohs(hdr->payload_len);
        if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
                return 0;

        return 1;
}

struct sk_buff *nf_reject_skb_v6_tcp_reset(struct net *net,
                                           struct sk_buff *oldskb,
                                           const struct net_device *dev,
                                           int hook)
{
        struct sk_buff *nskb;
        const struct tcphdr *oth;
        struct tcphdr _oth;
        unsigned int otcplen;
        struct ipv6hdr *nip6h;

        if (!nf_reject_ip6hdr_validate(oldskb))
                return NULL;

        oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
        if (!oth)
                return NULL;

        nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
                         LL_MAX_HEADER, GFP_ATOMIC);
        if (!nskb)
                return NULL;

        nskb->dev = (struct net_device *)dev;

        skb_reserve(nskb, LL_MAX_HEADER);
        nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
                                     READ_ONCE(net->ipv6.devconf_all->hop_limit));
        nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
        nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));

        return nskb;
}
EXPORT_SYMBOL_GPL(nf_reject_skb_v6_tcp_reset);

static bool nf_skb_is_icmp6_unreach(const struct sk_buff *skb)
{
        const struct ipv6hdr *ip6h = ipv6_hdr(skb);
        u8 proto = ip6h->nexthdr;
        u8 _type, *tp;
        int thoff;
        __be16 fo;

        thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);

        if (thoff < 0 || thoff >= skb->len || fo != 0)
                return false;

        if (proto != IPPROTO_ICMPV6)
                return false;

        tp = skb_header_pointer(skb,
                                thoff + offsetof(struct icmp6hdr, icmp6_type),
                                sizeof(_type), &_type);

        if (!tp)
                return false;

        return *tp == ICMPV6_DEST_UNREACH;
}

struct sk_buff *nf_reject_skb_v6_unreach(struct net *net,
                                         struct sk_buff *oldskb,
                                         const struct net_device *dev,
                                         int hook, u8 code)
{
        struct sk_buff *nskb;
        struct ipv6hdr *nip6h;
        struct icmp6hdr *icmp6h;
        unsigned int len;

        if (!nf_reject_ip6hdr_validate(oldskb))
                return NULL;

        /* Don't reply to ICMPV6_DEST_UNREACH with ICMPV6_DEST_UNREACH */
        if (nf_skb_is_icmp6_unreach(oldskb))
                return NULL;

        /* Include "As much of invoking packet as possible without the ICMPv6
         * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
         */
        len = min_t(unsigned int, 1220, oldskb->len);

        if (!pskb_may_pull(oldskb, len))
                return NULL;

        if (!nf_reject_v6_csum_ok(oldskb, hook))
                return NULL;

        nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
                         LL_MAX_HEADER + len, GFP_ATOMIC);
        if (!nskb)
                return NULL;

        nskb->dev = (struct net_device *)dev;

        skb_reserve(nskb, LL_MAX_HEADER);
        nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
                                     READ_ONCE(net->ipv6.devconf_all->hop_limit));

        skb_reset_transport_header(nskb);
        icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
        icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
        icmp6h->icmp6_code = code;

        skb_put_data(nskb, skb_network_header(oldskb), len);
        nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));

        icmp6h->icmp6_cksum =
                csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
                                nskb->len - sizeof(struct ipv6hdr),
                                IPPROTO_ICMPV6,
                                csum_partial(icmp6h,
                                             nskb->len - sizeof(struct ipv6hdr),
                                             0));

        return nskb;
}
EXPORT_SYMBOL_GPL(nf_reject_skb_v6_unreach);

static const struct tcphdr *
nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
                         struct tcphdr *otcph,
                         unsigned int *otcplen, int hook)
{
        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
        u8 proto;
        __be16 frag_off;
        int tcphoff;

        proto = oip6h->nexthdr;
        tcphoff = ipv6_skip_exthdr(oldskb, ((u8 *)(oip6h + 1) - oldskb->data),
                                   &proto, &frag_off);

        if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
                pr_debug("Cannot get TCP header.\n");
                return NULL;
        }

        *otcplen = oldskb->len - tcphoff;

        /* IP header checks: fragment, too short. */
        if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
                pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
                         proto, *otcplen);
                return NULL;
        }

        otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
                                   otcph);
        if (otcph == NULL)
                return NULL;

        /* No RST for RST. */
        if (otcph->rst) {
                pr_debug("RST is set\n");
                return NULL;
        }

        /* Check checksum. */
        if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
                pr_debug("TCP checksum is invalid\n");
                return NULL;
        }

        return otcph;
}

static struct ipv6hdr *
nf_reject_ip6hdr_put(struct sk_buff *nskb,
                     const struct sk_buff *oldskb,
                     __u8 protocol, int hoplimit)
{
        struct ipv6hdr *ip6h;
        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
#define DEFAULT_TOS_VALUE       0x0U
        const __u8 tclass = DEFAULT_TOS_VALUE;

        skb_put(nskb, sizeof(struct ipv6hdr));
        skb_reset_network_header(nskb);
        ip6h = ipv6_hdr(nskb);
        ip6_flow_hdr(ip6h, tclass, 0);
        ip6h->hop_limit = hoplimit;
        ip6h->nexthdr = protocol;
        ip6h->saddr = oip6h->daddr;
        ip6h->daddr = oip6h->saddr;

        nskb->protocol = htons(ETH_P_IPV6);

        return ip6h;
}

static void
nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
                         const struct sk_buff *oldskb,
                         const struct tcphdr *oth, unsigned int otcplen)
{
        struct tcphdr *tcph;

        skb_reset_transport_header(nskb);
        tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
        /* Truncate to length (no data) */
        tcph->doff = sizeof(struct tcphdr)/4;
        tcph->source = oth->dest;
        tcph->dest = oth->source;

        if (oth->ack) {
                tcph->seq = oth->ack_seq;
        } else {
                tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
                                      otcplen - (oth->doff<<2));
                tcph->ack = 1;
        }

        tcph->rst = 1;

        /* Adjust TCP checksum */
        tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
                                      &ipv6_hdr(nskb)->daddr,
                                      sizeof(struct tcphdr), IPPROTO_TCP,
                                      csum_partial(tcph,
                                                   sizeof(struct tcphdr), 0));
}

static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
{
        struct dst_entry *dst = NULL;
        struct flowi fl;

        memset(&fl, 0, sizeof(struct flowi));
        fl.u.ip6.daddr = ipv6_hdr(skb_in)->saddr;
        nf_ip6_route(dev_net(skb_in->dev), &dst, &fl, false);
        if (!dst)
                return -1;

        skb_dst_set(skb_in, dst);
        return 0;
}

void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
                    int hook)
{
        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
        struct dst_entry *dst = NULL;
        const struct tcphdr *otcph;
        struct sk_buff *nskb;
        struct tcphdr _otcph;
        unsigned int otcplen;
        struct flowi6 fl6;

        if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
            (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
                pr_debug("addr is not unicast.\n");
                return;
        }

        otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
        if (!otcph)
                return;

        memset(&fl6, 0, sizeof(fl6));
        fl6.flowi6_proto = IPPROTO_TCP;
        fl6.saddr = oip6h->daddr;
        fl6.daddr = oip6h->saddr;
        fl6.fl6_sport = otcph->dest;
        fl6.fl6_dport = otcph->source;

        if (!skb_dst(oldskb)) {
                nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
                if (!dst)
                        return;
                skb_dst_set(oldskb, dst);
        }

        fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst_dev(oldskb));
        fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark);
        security_skb_classify_flow(oldskb, flowi6_to_flowi_common(&fl6));
        dst = ip6_route_output(net, NULL, &fl6);
        if (dst->error) {
                dst_release(dst);
                return;
        }
        dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
        if (IS_ERR(dst))
                return;

        nskb = alloc_skb(LL_MAX_HEADER + sizeof(struct ipv6hdr) +
                         sizeof(struct tcphdr) + dst->trailer_len,
                         GFP_ATOMIC);

        if (!nskb) {
                net_dbg_ratelimited("cannot alloc skb\n");
                dst_release(dst);
                return;
        }

        skb_dst_set(nskb, dst);

        nskb->mark = fl6.flowi6_mark;

        skb_reserve(nskb, LL_MAX_HEADER);
        nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP, ip6_dst_hoplimit(dst));
        nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);

        nf_ct_attach(nskb, oldskb);
        nf_ct_set_closing(skb_nfct(oldskb));

#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        /* If we use ip6_local_out for bridged traffic, the MAC source on
         * the RST will be ours, instead of the destination's.  This confuses
         * some routers/firewalls, and they drop the packet.  So we need to
         * build the eth header using the original destination's MAC as the
         * source, and send the RST packet directly.
         */
        if (nf_bridge_info_exists(oldskb)) {
                struct ethhdr *oeth = eth_hdr(oldskb);
                struct ipv6hdr *ip6h = ipv6_hdr(nskb);
                struct net_device *br_indev;

                br_indev = nf_bridge_get_physindev(oldskb, net);
                if (!br_indev) {
                        kfree_skb(nskb);
                        return;
                }

                nskb->dev = br_indev;
                nskb->protocol = htons(ETH_P_IPV6);
                ip6h->payload_len = htons(sizeof(struct tcphdr));
                if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
                                    oeth->h_source, oeth->h_dest, nskb->len) < 0) {
                        kfree_skb(nskb);
                        return;
                }
                dev_queue_xmit(nskb);
        } else
#endif
                ip6_local_out(net, sk, nskb);
}
EXPORT_SYMBOL_GPL(nf_send_reset6);

static bool reject6_csum_ok(struct sk_buff *skb, int hook)
{
        const struct ipv6hdr *ip6h = ipv6_hdr(skb);
        int thoff;
        __be16 fo;
        u8 proto;

        if (skb_csum_unnecessary(skb))
                return true;

        proto = ip6h->nexthdr;
        thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);

        if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
                return false;

        if (!nf_reject_verify_csum(skb, thoff, proto))
                return true;

        return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
}

void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
                      unsigned char code, unsigned int hooknum)
{
        if (!reject6_csum_ok(skb_in, hooknum))
                return;

        if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
                skb_in->dev = net->loopback_dev;

        if (!skb_dst(skb_in) && nf_reject6_fill_skb_dst(skb_in) < 0)
                return;

        icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
}
EXPORT_SYMBOL_GPL(nf_send_unreach6);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("IPv6 packet rejection core");