// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (C) 2010: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
 * Copyright (C) 2015: Linus Lüssing <linus.luessing@c0d3.blue>
 *
 * Based on the MLD support added to br_multicast.c by YOSHIFUJI Hideaki.
 */

#include <linux/skbuff.h>
#include <net/ipv6.h>
#include <net/mld.h>
#include <net/addrconf.h>
#include <net/ip6_checksum.h>

static int ipv6_mc_check_ip6hdr(struct sk_buff *skb)
{
        const struct ipv6hdr *ip6h;
        unsigned int len;
        unsigned int offset = skb_network_offset(skb) + sizeof(*ip6h);

        if (!pskb_may_pull(skb, offset))
                return -EINVAL;

        ip6h = ipv6_hdr(skb);

        if (ip6h->version != 6)
                return -EINVAL;

        len = offset + ntohs(ip6h->payload_len);
        if (skb->len < len || len <= offset)
                return -EINVAL;

        skb_set_transport_header(skb, offset);

        return 0;
}

static int ipv6_mc_check_exthdrs(struct sk_buff *skb)
{
        const struct ipv6hdr *ip6h;
        int offset;
        u8 nexthdr;
        __be16 frag_off;

        ip6h = ipv6_hdr(skb);

        if (ip6h->nexthdr != IPPROTO_HOPOPTS)
                return -ENOMSG;

        nexthdr = ip6h->nexthdr;
        offset = skb_network_offset(skb) + sizeof(*ip6h);
        offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);

        if (offset < 0)
                return -EINVAL;

        if (nexthdr != IPPROTO_ICMPV6)
                return -ENOMSG;

        skb_set_transport_header(skb, offset);

        return 0;
}

static int ipv6_mc_check_mld_reportv2(struct sk_buff *skb)
{
        unsigned int len = skb_transport_offset(skb);

        len += sizeof(struct mld2_report);

        return ipv6_mc_may_pull(skb, len) ? 0 : -EINVAL;
}

static int ipv6_mc_check_mld_query(struct sk_buff *skb)
{
        unsigned int transport_len = ipv6_transport_len(skb);
        struct mld_msg *mld;
        unsigned int len;

        /* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
        if (!(ipv6_addr_type(&ipv6_hdr(skb)->saddr) & IPV6_ADDR_LINKLOCAL))
                return -EINVAL;

        /* MLDv1? */
        if (transport_len != sizeof(struct mld_msg)) {
                /* or MLDv2? */
                if (transport_len < sizeof(struct mld2_query))
                        return -EINVAL;

                len = skb_transport_offset(skb) + sizeof(struct mld2_query);
                if (!ipv6_mc_may_pull(skb, len))
                        return -EINVAL;
        }

        mld = (struct mld_msg *)skb_transport_header(skb);

        /* RFC2710+RFC3810 (MLDv1+MLDv2) require the multicast link layer
         * all-nodes destination address (ff02::1) for general queries
         */
        if (ipv6_addr_any(&mld->mld_mca) &&
            !ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
                return -EINVAL;

        return 0;
}

static int ipv6_mc_check_mld_msg(struct sk_buff *skb)
{
        unsigned int len = skb_transport_offset(skb) + sizeof(struct mld_msg);
        struct mld_msg *mld;

        if (!ipv6_mc_may_pull(skb, len))
                return -ENODATA;

        mld = (struct mld_msg *)skb_transport_header(skb);

        switch (mld->mld_type) {
        case ICMPV6_MGM_REDUCTION:
        case ICMPV6_MGM_REPORT:
                return 0;
        case ICMPV6_MLD2_REPORT:
                return ipv6_mc_check_mld_reportv2(skb);
        case ICMPV6_MGM_QUERY:
                return ipv6_mc_check_mld_query(skb);
        default:
                return -ENODATA;
        }
}

static inline __sum16 ipv6_mc_validate_checksum(struct sk_buff *skb)
{
        return skb_checksum_validate(skb, IPPROTO_ICMPV6, ip6_compute_pseudo);
}

static int ipv6_mc_check_icmpv6(struct sk_buff *skb)
{
        unsigned int len = skb_transport_offset(skb) + sizeof(struct icmp6hdr);
        unsigned int transport_len = ipv6_transport_len(skb);
        struct sk_buff *skb_chk;

        if (!ipv6_mc_may_pull(skb, len))
                return -EINVAL;

        skb_chk = skb_checksum_trimmed(skb, transport_len,
                                       ipv6_mc_validate_checksum);
        if (!skb_chk)
                return -EINVAL;

        if (skb_chk != skb)
                kfree_skb(skb_chk);

        return 0;
}

/**
 * ipv6_mc_check_mld - checks whether this is a sane MLD packet
 * @skb: the skb to validate
 *
 * Checks whether an IPv6 packet is a valid MLD packet. If so sets
 * skb transport header accordingly and returns zero.
 *
 * -EINVAL: A broken packet was detected, i.e. it violates some internet
 *  standard
 * -ENOMSG: IP header validation succeeded but it is not an ICMPv6 packet
 *  with a hop-by-hop option.
 * -ENODATA: IP+ICMPv6 header with hop-by-hop option validation succeeded
 *  but it is not an MLD packet.
 * -ENOMEM: A memory allocation failure happened.
 *
 * Caller needs to set the skb network header and free any returned skb if it
 * differs from the provided skb.
 */
int ipv6_mc_check_mld(struct sk_buff *skb)
{
        int ret;

        ret = ipv6_mc_check_ip6hdr(skb);
        if (ret < 0)
                return ret;

        ret = ipv6_mc_check_exthdrs(skb);
        if (ret < 0)
                return ret;

        ret = ipv6_mc_check_icmpv6(skb);
        if (ret < 0)
                return ret;

        return ipv6_mc_check_mld_msg(skb);
}
EXPORT_SYMBOL(ipv6_mc_check_mld);