// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      IPv6 fragment reassembly
 *      Linux INET6 implementation
 *
 *      Authors:
 *      Pedro Roque             <roque@di.fc.ul.pt>
 *
 *      Based on: net/ipv4/ip_fragment.c
 */

/*
 *      Fixes:
 *      Andi Kleen      Make it work with multiple hosts.
 *                      More RFC compliance.
 *
 *      Horst von Brand Add missing #include <linux/string.h>
 *      Alexey Kuznetsov        SMP races, threading, cleanup.
 *      Patrick McHardy         LRU queue of frag heads for evictor.
 *      Mitsuru KANDA @USAGI    Register inet6_protocol{}.
 *      David Stevens and
 *      YOSHIFUJI,H. @USAGI     Always remove fragment header to
 *                              calculate ICV correctly.
 */

#define pr_fmt(fmt) "IPv6: " fmt

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/jiffies.h>
#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/ipv6.h>
#include <linux/icmpv6.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/tcp.h>
#include <linux/udp.h>

#include <net/sock.h>
#include <net/snmp.h>

#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>
#include <net/ipv6_frag.h>
#include <net/inet_ecn.h>

static const char ip6_frag_cache_name[] = "ip6-frags";

static u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
{
        return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
}

static struct inet_frags ip6_frags;

static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
                          struct sk_buff *prev_tail, struct net_device *dev);

static void ip6_frag_expire(struct timer_list *t)
{
        struct inet_frag_queue *frag = from_timer(frag, t, timer);
        struct frag_queue *fq;

        fq = container_of(frag, struct frag_queue, q);

        ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
}

static struct frag_queue *
fq_find(struct net *net, __be32 id, const struct ipv6hdr *hdr, int iif)
{
        struct frag_v6_compare_key key = {
                .id = id,
                .saddr = hdr->saddr,
                .daddr = hdr->daddr,
                .user = IP6_DEFRAG_LOCAL_DELIVER,
                .iif = iif,
        };
        struct inet_frag_queue *q;

        if (!(ipv6_addr_type(&hdr->daddr) & (IPV6_ADDR_MULTICAST |
                                            IPV6_ADDR_LINKLOCAL)))
                key.iif = 0;

        q = inet_frag_find(net->ipv6.fqdir, &key);
        if (!q)
                return NULL;

        return container_of(q, struct frag_queue, q);
}

static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
                          struct frag_hdr *fhdr, int nhoff,
                          u32 *prob_offset)
{
        struct net *net = dev_net(skb_dst(skb)->dev);
        int offset, end, fragsize;
        struct sk_buff *prev_tail;
        struct net_device *dev;
        int err = -ENOENT;
        u8 ecn;

        if (fq->q.flags & INET_FRAG_COMPLETE)
                goto err;

        err = -EINVAL;
        offset = ntohs(fhdr->frag_off) & ~0x7;
        end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
                        ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

        if ((unsigned int)end > IPV6_MAXPLEN) {
                *prob_offset = (u8 *)&fhdr->frag_off - skb_network_header(skb);
                /* note that if prob_offset is set, the skb is freed elsewhere,
                 * we do not free it here.
                 */
                return -1;
        }

        ecn = ip6_frag_ecn(ipv6_hdr(skb));

        if (skb->ip_summed == CHECKSUM_COMPLETE) {
                const unsigned char *nh = skb_network_header(skb);
                skb->csum = csum_sub(skb->csum,
                                     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
                                                  0));
        }

        /* Is this the final fragment? */
        if (!(fhdr->frag_off & htons(IP6_MF))) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrupted.
                 */
                if (end < fq->q.len ||
                    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len))
                        goto discard_fq;
                fq->q.flags |= INET_FRAG_LAST_IN;
                fq->q.len = end;
        } else {
                /* Check if the fragment is rounded to 8 bytes.
                 * Required by the RFC.
                 */
                if (end & 0x7) {
                        /* RFC2460 says always send parameter problem in
                         * this case. -DaveM
                         */
                        *prob_offset = offsetof(struct ipv6hdr, payload_len);
                        return -1;
                }
                if (end > fq->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->q.flags & INET_FRAG_LAST_IN)
                                goto discard_fq;
                        fq->q.len = end;
                }
        }

        if (end == offset)
                goto discard_fq;

        err = -ENOMEM;
        /* Point into the IP datagram 'data' part. */
        if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
                goto discard_fq;

        err = pskb_trim_rcsum(skb, end - offset);
        if (err)
                goto discard_fq;

        /* Note : skb->rbnode and skb->dev share the same location. */
        dev = skb->dev;
        /* Makes sure compiler wont do silly aliasing games */
        barrier();

        prev_tail = fq->q.fragments_tail;
        err = inet_frag_queue_insert(&fq->q, skb, offset, end);
        if (err)
                goto insert_error;

        if (dev)
                fq->iif = dev->ifindex;

        fq->q.stamp = skb->tstamp;
        fq->q.meat += skb->len;
        fq->ecn |= ecn;
        add_frag_mem_limit(fq->q.fqdir, skb->truesize);

        fragsize = -skb_network_offset(skb) + skb->len;
        if (fragsize > fq->q.max_size)
                fq->q.max_size = fragsize;

        /* The first fragment.
         * nhoffset is obtained from the first fragment, of course.
         */
        if (offset == 0) {
                fq->nhoffset = nhoff;
                fq->q.flags |= INET_FRAG_FIRST_IN;
        }

        if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            fq->q.meat == fq->q.len) {
                unsigned long orefdst = skb->_skb_refdst;

                skb->_skb_refdst = 0UL;
                err = ip6_frag_reasm(fq, skb, prev_tail, dev);
                skb->_skb_refdst = orefdst;
                return err;
        }

        skb_dst_drop(skb);
        return -EINPROGRESS;

insert_error:
        if (err == IPFRAG_DUP) {
                kfree_skb(skb);
                return -EINVAL;
        }
        err = -EINVAL;
        __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                        IPSTATS_MIB_REASM_OVERLAPS);
discard_fq:
        inet_frag_kill(&fq->q);
        __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                        IPSTATS_MIB_REASMFAILS);
err:
        kfree_skb(skb);
        return err;
}

/*
 *      Check if this packet is complete.
 *
 *      It is called with locked fq, and caller must check that
 *      queue is eligible for reassembly i.e. it is not COMPLETE,
 *      the last and the first frames arrived and all the bits are here.
 */
static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
                          struct sk_buff *prev_tail, struct net_device *dev)
{
        struct net *net = fq->q.fqdir->net;
        unsigned int nhoff;
        void *reasm_data;
        int payload_len;
        u8 ecn;

        inet_frag_kill(&fq->q);

        ecn = ip_frag_ecn_table[fq->ecn];
        if (unlikely(ecn == 0xff))
                goto out_fail;

        reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
        if (!reasm_data)
                goto out_oom;

        payload_len = ((skb->data - skb_network_header(skb)) -
                       sizeof(struct ipv6hdr) + fq->q.len -
                       sizeof(struct frag_hdr));
        if (payload_len > IPV6_MAXPLEN)
                goto out_oversize;

        /* We have to remove fragment header from datagram and to relocate
         * header in order to calculate ICV correctly. */
        nhoff = fq->nhoffset;
        skb_network_header(skb)[nhoff] = skb_transport_header(skb)[0];
        memmove(skb->head + sizeof(struct frag_hdr), skb->head,
                (skb->data - skb->head) - sizeof(struct frag_hdr));
        if (skb_mac_header_was_set(skb))
                skb->mac_header += sizeof(struct frag_hdr);
        skb->network_header += sizeof(struct frag_hdr);

        skb_reset_transport_header(skb);

        inet_frag_reasm_finish(&fq->q, skb, reasm_data, true);

        skb->dev = dev;
        ipv6_hdr(skb)->payload_len = htons(payload_len);
        ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
        IP6CB(skb)->nhoff = nhoff;
        IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
        IP6CB(skb)->frag_max_size = fq->q.max_size;

        /* Yes, and fold redundant checksum back. 8) */
        skb_postpush_rcsum(skb, skb_network_header(skb),
                           skb_network_header_len(skb));

        rcu_read_lock();
        __IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMOKS);
        rcu_read_unlock();
        fq->q.rb_fragments = RB_ROOT;
        fq->q.fragments_tail = NULL;
        fq->q.last_run_head = NULL;
        return 1;

out_oversize:
        net_dbg_ratelimited("ip6_frag_reasm: payload len = %d\n", payload_len);
        goto out_fail;
out_oom:
        net_dbg_ratelimited("ip6_frag_reasm: no memory for reassembly\n");
out_fail:
        rcu_read_lock();
        __IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMFAILS);
        rcu_read_unlock();
        inet_frag_kill(&fq->q);
        return -1;
}

static int ipv6_frag_rcv(struct sk_buff *skb)
{
        struct frag_hdr *fhdr;
        struct frag_queue *fq;
        const struct ipv6hdr *hdr = ipv6_hdr(skb);
        struct net *net = dev_net(skb_dst(skb)->dev);
        u8 nexthdr;
        int iif;

        if (IP6CB(skb)->flags & IP6SKB_FRAGMENTED)
                goto fail_hdr;

        __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMREQDS);

        /* Jumbo payload inhibits frag. header */
        if (hdr->payload_len == 0)
                goto fail_hdr;

        if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
                                 sizeof(struct frag_hdr))))
                goto fail_hdr;

        hdr = ipv6_hdr(skb);
        fhdr = (struct frag_hdr *)skb_transport_header(skb);

        if (!(fhdr->frag_off & htons(IP6_OFFSET | IP6_MF))) {
                /* It is not a fragmented frame */
                skb->transport_header += sizeof(struct frag_hdr);
                __IP6_INC_STATS(net,
                                ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMOKS);

                IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
                IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
                IP6CB(skb)->frag_max_size = ntohs(hdr->payload_len) +
                                            sizeof(struct ipv6hdr);
                return 1;
        }

        /* RFC 8200, Section 4.5 Fragment Header:
         * If the first fragment does not include all headers through an
         * Upper-Layer header, then that fragment should be discarded and
         * an ICMP Parameter Problem, Code 3, message should be sent to
         * the source of the fragment, with the Pointer field set to zero.
         */
        nexthdr = hdr->nexthdr;
        if (ipv6frag_thdr_truncated(skb, skb_transport_offset(skb), &nexthdr)) {
                __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
                                IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
                return -1;
        }

        iif = skb->dev ? skb->dev->ifindex : 0;
        fq = fq_find(net, fhdr->identification, hdr, iif);
        if (fq) {
                u32 prob_offset = 0;
                int ret;

                spin_lock(&fq->q.lock);

                fq->iif = iif;
                ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff,
                                     &prob_offset);

                spin_unlock(&fq->q.lock);
                inet_frag_put(&fq->q);
                if (prob_offset) {
                        __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
                                        IPSTATS_MIB_INHDRERRORS);
                        /* icmpv6_param_prob() calls kfree_skb(skb) */
                        icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, prob_offset);
                }
                return ret;
        }

        __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -1;

fail_hdr:
        __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
                        IPSTATS_MIB_INHDRERRORS);
        icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb_network_header_len(skb));
        return -1;
}

static const struct inet6_protocol frag_protocol = {
        .handler        =       ipv6_frag_rcv,
        .flags          =       INET6_PROTO_NOPOLICY,
};

#ifdef CONFIG_SYSCTL

static struct ctl_table ip6_frags_ns_ctl_table[] = {
        {
                .procname       = "ip6frag_high_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "ip6frag_low_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "ip6frag_time",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

/* secret interval has been deprecated */
static int ip6_frags_secret_interval_unused;
static struct ctl_table ip6_frags_ctl_table[] = {
        {
                .procname       = "ip6frag_secret_interval",
                .data           = &ip6_frags_secret_interval_unused,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

static int __net_init ip6_frags_ns_sysctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;

        table = ip6_frags_ns_ctl_table;
        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(ip6_frags_ns_ctl_table), GFP_KERNEL);
                if (!table)
                        goto err_alloc;

        }
        table[0].data   = &net->ipv6.fqdir->high_thresh;
        table[0].extra1 = &net->ipv6.fqdir->low_thresh;
        table[1].data   = &net->ipv6.fqdir->low_thresh;
        table[1].extra2 = &net->ipv6.fqdir->high_thresh;
        table[2].data   = &net->ipv6.fqdir->timeout;

        hdr = register_net_sysctl(net, "net/ipv6", table);
        if (!hdr)
                goto err_reg;

        net->ipv6.sysctl.frags_hdr = hdr;
        return 0;

err_reg:
        if (!net_eq(net, &init_net))
                kfree(table);
err_alloc:
        return -ENOMEM;
}

static void __net_exit ip6_frags_ns_sysctl_unregister(struct net *net)
{
        struct ctl_table *table;

        table = net->ipv6.sysctl.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(net->ipv6.sysctl.frags_hdr);
        if (!net_eq(net, &init_net))
                kfree(table);
}

static struct ctl_table_header *ip6_ctl_header;

static int ip6_frags_sysctl_register(void)
{
        ip6_ctl_header = register_net_sysctl(&init_net, "net/ipv6",
                        ip6_frags_ctl_table);
        return ip6_ctl_header == NULL ? -ENOMEM : 0;
}

static void ip6_frags_sysctl_unregister(void)
{
        unregister_net_sysctl_table(ip6_ctl_header);
}
#else
static int ip6_frags_ns_sysctl_register(struct net *net)
{
        return 0;
}

static void ip6_frags_ns_sysctl_unregister(struct net *net)
{
}

static int ip6_frags_sysctl_register(void)
{
        return 0;
}

static void ip6_frags_sysctl_unregister(void)
{
}
#endif

static int __net_init ipv6_frags_init_net(struct net *net)
{
        int res;

        res = fqdir_init(&net->ipv6.fqdir, &ip6_frags, net);
        if (res < 0)
                return res;

        net->ipv6.fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
        net->ipv6.fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
        net->ipv6.fqdir->timeout = IPV6_FRAG_TIMEOUT;

        res = ip6_frags_ns_sysctl_register(net);
        if (res < 0)
                fqdir_exit(net->ipv6.fqdir);
        return res;
}

static void __net_exit ipv6_frags_pre_exit_net(struct net *net)
{
        fqdir_pre_exit(net->ipv6.fqdir);
}

static void __net_exit ipv6_frags_exit_net(struct net *net)
{
        ip6_frags_ns_sysctl_unregister(net);
        fqdir_exit(net->ipv6.fqdir);
}

static struct pernet_operations ip6_frags_ops = {
        .init           = ipv6_frags_init_net,
        .pre_exit       = ipv6_frags_pre_exit_net,
        .exit           = ipv6_frags_exit_net,
};

static const struct rhashtable_params ip6_rhash_params = {
        .head_offset            = offsetof(struct inet_frag_queue, node),
        .hashfn                 = ip6frag_key_hashfn,
        .obj_hashfn             = ip6frag_obj_hashfn,
        .obj_cmpfn              = ip6frag_obj_cmpfn,
        .automatic_shrinking    = true,
};

int __init ipv6_frag_init(void)
{
        int ret;

        ip6_frags.constructor = ip6frag_init;
        ip6_frags.destructor = NULL;
        ip6_frags.qsize = sizeof(struct frag_queue);
        ip6_frags.frag_expire = ip6_frag_expire;
        ip6_frags.frags_cache_name = ip6_frag_cache_name;
        ip6_frags.rhash_params = ip6_rhash_params;
        ret = inet_frags_init(&ip6_frags);
        if (ret)
                goto out;

        ret = inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT);
        if (ret)
                goto err_protocol;

        ret = ip6_frags_sysctl_register();
        if (ret)
                goto err_sysctl;

        ret = register_pernet_subsys(&ip6_frags_ops);
        if (ret)
                goto err_pernet;

out:
        return ret;

err_pernet:
        ip6_frags_sysctl_unregister();
err_sysctl:
        inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
err_protocol:
        inet_frags_fini(&ip6_frags);
        goto out;
}

void ipv6_frag_exit(void)
{
        ip6_frags_sysctl_unregister();
        unregister_pernet_subsys(&ip6_frags_ops);
        inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
        inet_frags_fini(&ip6_frags);
}