// SPDX-License-Identifier: GPL-2.0-or-later
/*      6LoWPAN fragment reassembly
 *
 *      Authors:
 *      Alexander Aring         <aar@pengutronix.de>
 *
 *      Based on: net/ipv6/reassembly.c
 */

#define pr_fmt(fmt) "6LoWPAN: " fmt

#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/export.h>

#include <net/ieee802154_netdev.h>
#include <net/6lowpan.h>
#include <net/ipv6_frag.h>
#include <net/inet_frag.h>
#include <net/ip.h>

#include "6lowpan_i.h"

static const char lowpan_frags_cache_name[] = "lowpan-frags";

static struct inet_frags lowpan_frags;

static int lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *skb,
                             struct sk_buff *prev,  struct net_device *ldev);

static void lowpan_frag_init(struct inet_frag_queue *q, const void *a)
{
        const struct frag_lowpan_compare_key *key = a;

        BUILD_BUG_ON(sizeof(*key) > sizeof(q->key));
        memcpy(&q->key, key, sizeof(*key));
}

static void lowpan_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);

        spin_lock(&fq->q.lock);

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

        inet_frag_kill(&fq->q);
out:
        spin_unlock(&fq->q.lock);
        inet_frag_put(&fq->q);
}

static inline struct lowpan_frag_queue *
fq_find(struct net *net, const struct lowpan_802154_cb *cb,
        const struct ieee802154_addr *src,
        const struct ieee802154_addr *dst)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);
        struct frag_lowpan_compare_key key = {};
        struct inet_frag_queue *q;

        key.tag = cb->d_tag;
        key.d_size = cb->d_size;
        key.src = *src;
        key.dst = *dst;

        q = inet_frag_find(ieee802154_lowpan->fqdir, &key);
        if (!q)
                return NULL;

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

static int lowpan_frag_queue(struct lowpan_frag_queue *fq,
                             struct sk_buff *skb, u8 frag_type)
{
        struct sk_buff *prev_tail;
        struct net_device *ldev;
        int end, offset, err;

        /* inet_frag_queue_* functions use skb->cb; see struct ipfrag_skb_cb
         * in inet_fragment.c
         */
        BUILD_BUG_ON(sizeof(struct lowpan_802154_cb) > sizeof(struct inet_skb_parm));
        BUILD_BUG_ON(sizeof(struct lowpan_802154_cb) > sizeof(struct inet6_skb_parm));

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

        offset = lowpan_802154_cb(skb)->d_offset << 3;
        end = lowpan_802154_cb(skb)->d_size;

        /* Is this the final fragment? */
        if (offset + skb->len == end) {
                /* 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 err;
                fq->q.flags |= INET_FRAG_LAST_IN;
                fq->q.len = end;
        } else {
                if (end > fq->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->q.flags & INET_FRAG_LAST_IN)
                                goto err;
                        fq->q.len = end;
                }
        }

        ldev = skb->dev;
        if (ldev)
                skb->dev = NULL;
        barrier();

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

        fq->q.stamp = skb->tstamp;
        if (frag_type == LOWPAN_DISPATCH_FRAG1)
                fq->q.flags |= INET_FRAG_FIRST_IN;

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

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

                skb->_skb_refdst = 0UL;
                res = lowpan_frag_reasm(fq, skb, prev_tail, ldev);
                skb->_skb_refdst = orefdst;
                return res;
        }
        skb_dst_drop(skb);

        return -1;
err:
        kfree_skb(skb);
        return -1;
}

/*      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 lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *skb,
                             struct sk_buff *prev_tail, struct net_device *ldev)
{
        void *reasm_data;

        inet_frag_kill(&fq->q);

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

        skb->dev = ldev;
        skb->tstamp = fq->q.stamp;
        fq->q.rb_fragments = RB_ROOT;
        fq->q.fragments_tail = NULL;
        fq->q.last_run_head = NULL;

        return 1;
out_oom:
        net_dbg_ratelimited("lowpan_frag_reasm: no memory for reassembly\n");
        return -1;
}

static int lowpan_frag_rx_handlers_result(struct sk_buff *skb,
                                          lowpan_rx_result res)
{
        switch (res) {
        case RX_QUEUED:
                return NET_RX_SUCCESS;
        case RX_CONTINUE:
                /* nobody cared about this packet */
                net_warn_ratelimited("%s: received unknown dispatch\n",
                                     __func__);

                /* fall-through */
        default:
                /* all others failure */
                return NET_RX_DROP;
        }
}

static lowpan_rx_result lowpan_frag_rx_h_iphc(struct sk_buff *skb)
{
        int ret;

        if (!lowpan_is_iphc(*skb_network_header(skb)))
                return RX_CONTINUE;

        ret = lowpan_iphc_decompress(skb);
        if (ret < 0)
                return RX_DROP;

        return RX_QUEUED;
}

static int lowpan_invoke_frag_rx_handlers(struct sk_buff *skb)
{
        lowpan_rx_result res;

#define CALL_RXH(rxh)                   \
        do {                            \
                res = rxh(skb); \
                if (res != RX_CONTINUE) \
                        goto rxh_next;  \
        } while (0)

        /* likely at first */
        CALL_RXH(lowpan_frag_rx_h_iphc);
        CALL_RXH(lowpan_rx_h_ipv6);

rxh_next:
        return lowpan_frag_rx_handlers_result(skb, res);
#undef CALL_RXH
}

#define LOWPAN_FRAG_DGRAM_SIZE_HIGH_MASK        0x07
#define LOWPAN_FRAG_DGRAM_SIZE_HIGH_SHIFT       8

static int lowpan_get_cb(struct sk_buff *skb, u8 frag_type,
                         struct lowpan_802154_cb *cb)
{
        bool fail;
        u8 high = 0, low = 0;
        __be16 d_tag = 0;

        fail = lowpan_fetch_skb(skb, &high, 1);
        fail |= lowpan_fetch_skb(skb, &low, 1);
        /* remove the dispatch value and use first three bits as high value
         * for the datagram size
         */
        cb->d_size = (high & LOWPAN_FRAG_DGRAM_SIZE_HIGH_MASK) <<
                LOWPAN_FRAG_DGRAM_SIZE_HIGH_SHIFT | low;
        fail |= lowpan_fetch_skb(skb, &d_tag, 2);
        cb->d_tag = ntohs(d_tag);

        if (frag_type == LOWPAN_DISPATCH_FRAGN) {
                fail |= lowpan_fetch_skb(skb, &cb->d_offset, 1);
        } else {
                skb_reset_network_header(skb);
                cb->d_offset = 0;
                /* check if datagram_size has ipv6hdr on FRAG1 */
                fail |= cb->d_size < sizeof(struct ipv6hdr);
                /* check if we can dereference the dispatch value */
                fail |= !skb->len;
        }

        if (unlikely(fail))
                return -EIO;

        return 0;
}

int lowpan_frag_rcv(struct sk_buff *skb, u8 frag_type)
{
        struct lowpan_frag_queue *fq;
        struct net *net = dev_net(skb->dev);
        struct lowpan_802154_cb *cb = lowpan_802154_cb(skb);
        struct ieee802154_hdr hdr = {};
        int err;

        if (ieee802154_hdr_peek_addrs(skb, &hdr) < 0)
                goto err;

        err = lowpan_get_cb(skb, frag_type, cb);
        if (err < 0)
                goto err;

        if (frag_type == LOWPAN_DISPATCH_FRAG1) {
                err = lowpan_invoke_frag_rx_handlers(skb);
                if (err == NET_RX_DROP)
                        goto err;
        }

        if (cb->d_size > IPV6_MIN_MTU) {
                net_warn_ratelimited("lowpan_frag_rcv: datagram size exceeds MTU\n");
                goto err;
        }

        fq = fq_find(net, cb, &hdr.source, &hdr.dest);
        if (fq != NULL) {
                int ret;

                spin_lock(&fq->q.lock);
                ret = lowpan_frag_queue(fq, skb, frag_type);
                spin_unlock(&fq->q.lock);

                inet_frag_put(&fq->q);
                return ret;
        }

err:
        kfree_skb(skb);
        return -1;
}

#ifdef CONFIG_SYSCTL

static struct ctl_table lowpan_frags_ns_ctl_table[] = {
        {
                .procname       = "6lowpanfrag_high_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "6lowpanfrag_low_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "6lowpanfrag_time",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

/* secret interval has been deprecated */
static int lowpan_frags_secret_interval_unused;
static struct ctl_table lowpan_frags_ctl_table[] = {
        {
                .procname       = "6lowpanfrag_secret_interval",
                .data           = &lowpan_frags_secret_interval_unused,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

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

                /* Don't export sysctls to unprivileged users */
                if (net->user_ns != &init_user_ns)
                        table[0].procname = NULL;
        }

        table[0].data   = &ieee802154_lowpan->fqdir->high_thresh;
        table[0].extra1 = &ieee802154_lowpan->fqdir->low_thresh;
        table[1].data   = &ieee802154_lowpan->fqdir->low_thresh;
        table[1].extra2 = &ieee802154_lowpan->fqdir->high_thresh;
        table[2].data   = &ieee802154_lowpan->fqdir->timeout;

        hdr = register_net_sysctl(net, "net/ieee802154/6lowpan", table);
        if (hdr == NULL)
                goto err_reg;

        ieee802154_lowpan->sysctl.frags_hdr = hdr;
        return 0;

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

static void __net_exit lowpan_frags_ns_sysctl_unregister(struct net *net)
{
        struct ctl_table *table;
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        table = ieee802154_lowpan->sysctl.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(ieee802154_lowpan->sysctl.frags_hdr);
        if (!net_eq(net, &init_net))
                kfree(table);
}

static struct ctl_table_header *lowpan_ctl_header;

static int __init lowpan_frags_sysctl_register(void)
{
        lowpan_ctl_header = register_net_sysctl(&init_net,
                                                "net/ieee802154/6lowpan",
                                                lowpan_frags_ctl_table);
        return lowpan_ctl_header == NULL ? -ENOMEM : 0;
}

static void lowpan_frags_sysctl_unregister(void)
{
        unregister_net_sysctl_table(lowpan_ctl_header);
}
#else
static inline int lowpan_frags_ns_sysctl_register(struct net *net)
{
        return 0;
}

static inline void lowpan_frags_ns_sysctl_unregister(struct net *net)
{
}

static inline int __init lowpan_frags_sysctl_register(void)
{
        return 0;
}

static inline void lowpan_frags_sysctl_unregister(void)
{
}
#endif

static int __net_init lowpan_frags_init_net(struct net *net)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);
        int res;


        res = fqdir_init(&ieee802154_lowpan->fqdir, &lowpan_frags, net);
        if (res < 0)
                return res;

        ieee802154_lowpan->fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
        ieee802154_lowpan->fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
        ieee802154_lowpan->fqdir->timeout = IPV6_FRAG_TIMEOUT;

        res = lowpan_frags_ns_sysctl_register(net);
        if (res < 0)
                fqdir_exit(ieee802154_lowpan->fqdir);
        return res;
}

static void __net_exit lowpan_frags_pre_exit_net(struct net *net)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        fqdir_pre_exit(ieee802154_lowpan->fqdir);
}

static void __net_exit lowpan_frags_exit_net(struct net *net)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        lowpan_frags_ns_sysctl_unregister(net);
        fqdir_exit(ieee802154_lowpan->fqdir);
}

static struct pernet_operations lowpan_frags_ops = {
        .init           = lowpan_frags_init_net,
        .pre_exit       = lowpan_frags_pre_exit_net,
        .exit           = lowpan_frags_exit_net,
};

static u32 lowpan_key_hashfn(const void *data, u32 len, u32 seed)
{
        return jhash2(data,
                      sizeof(struct frag_lowpan_compare_key) / sizeof(u32), seed);
}

static u32 lowpan_obj_hashfn(const void *data, u32 len, u32 seed)
{
        const struct inet_frag_queue *fq = data;

        return jhash2((const u32 *)&fq->key,
                      sizeof(struct frag_lowpan_compare_key) / sizeof(u32), seed);
}

static int lowpan_obj_cmpfn(struct rhashtable_compare_arg *arg, const void *ptr)
{
        const struct frag_lowpan_compare_key *key = arg->key;
        const struct inet_frag_queue *fq = ptr;

        return !!memcmp(&fq->key, key, sizeof(*key));
}

static const struct rhashtable_params lowpan_rhash_params = {
        .head_offset            = offsetof(struct inet_frag_queue, node),
        .hashfn                 = lowpan_key_hashfn,
        .obj_hashfn             = lowpan_obj_hashfn,
        .obj_cmpfn              = lowpan_obj_cmpfn,
        .automatic_shrinking    = true,
};

int __init lowpan_net_frag_init(void)
{
        int ret;

        lowpan_frags.constructor = lowpan_frag_init;
        lowpan_frags.destructor = NULL;
        lowpan_frags.qsize = sizeof(struct frag_queue);
        lowpan_frags.frag_expire = lowpan_frag_expire;
        lowpan_frags.frags_cache_name = lowpan_frags_cache_name;
        lowpan_frags.rhash_params = lowpan_rhash_params;
        ret = inet_frags_init(&lowpan_frags);
        if (ret)
                goto out;

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

        ret = register_pernet_subsys(&lowpan_frags_ops);
        if (ret)
                goto err_pernet;
out:
        return ret;
err_pernet:
        lowpan_frags_sysctl_unregister();
err_sysctl:
        inet_frags_fini(&lowpan_frags);
        return ret;
}

void lowpan_net_frag_exit(void)
{
        lowpan_frags_sysctl_unregister();
        unregister_pernet_subsys(&lowpan_frags_ops);
        inet_frags_fini(&lowpan_frags);
}