// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
#include <linux/if_vlan.h>
#include <net/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#include <net/dst.h>
#include <net/ip.h>
#include <net/ip6_fib.h>

struct sch_frag_data {
        unsigned long dst;
        struct qdisc_skb_cb cb;
        __be16 inner_protocol;
        u16 vlan_tci;
        __be16 vlan_proto;
        unsigned int l2_len;
        u8 l2_data[VLAN_ETH_HLEN];
        int (*xmit)(struct sk_buff *skb);
        local_lock_t bh_lock;
};

static DEFINE_PER_CPU(struct sch_frag_data, sch_frag_data_storage) = {
        .bh_lock = INIT_LOCAL_LOCK(bh_lock),
};

static int sch_frag_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct sch_frag_data *data = this_cpu_ptr(&sch_frag_data_storage);

        lockdep_assert_held(&data->bh_lock);
        if (skb_cow_head(skb, data->l2_len) < 0) {
                kfree_skb(skb);
                return -ENOMEM;
        }

        __skb_dst_copy(skb, data->dst);
        *qdisc_skb_cb(skb) = data->cb;
        skb->inner_protocol = data->inner_protocol;
        if (data->vlan_tci & VLAN_CFI_MASK)
                __vlan_hwaccel_put_tag(skb, data->vlan_proto,
                                       data->vlan_tci & ~VLAN_CFI_MASK);
        else
                __vlan_hwaccel_clear_tag(skb);

        /* Reconstruct the MAC header.  */
        skb_push(skb, data->l2_len);
        memcpy(skb->data, &data->l2_data, data->l2_len);
        skb_postpush_rcsum(skb, skb->data, data->l2_len);
        skb_reset_mac_header(skb);

        return data->xmit(skb);
}

static void sch_frag_prepare_frag(struct sk_buff *skb,
                                  int (*xmit)(struct sk_buff *skb))
{
        unsigned int hlen = skb_network_offset(skb);
        struct sch_frag_data *data;

        data = this_cpu_ptr(&sch_frag_data_storage);
        data->dst = skb->_skb_refdst;
        data->cb = *qdisc_skb_cb(skb);
        data->xmit = xmit;
        data->inner_protocol = skb->inner_protocol;
        if (skb_vlan_tag_present(skb))
                data->vlan_tci = skb_vlan_tag_get(skb) | VLAN_CFI_MASK;
        else
                data->vlan_tci = 0;
        data->vlan_proto = skb->vlan_proto;
        data->l2_len = hlen;
        memcpy(&data->l2_data, skb->data, hlen);

        memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
        skb_pull(skb, hlen);
}

static unsigned int
sch_frag_dst_get_mtu(const struct dst_entry *dst)
{
        return dst->dev->mtu;
}

static struct dst_ops sch_frag_dst_ops = {
        .family = AF_UNSPEC,
        .mtu = sch_frag_dst_get_mtu,
};

static int sch_fragment(struct net *net, struct sk_buff *skb,
                        u16 mru, int (*xmit)(struct sk_buff *skb))
{
        int ret = -1;

        if (skb_network_offset(skb) > VLAN_ETH_HLEN) {
                net_warn_ratelimited("L2 header too long to fragment\n");
                goto err;
        }

        if (skb_protocol(skb, true) == htons(ETH_P_IP)) {
                struct rtable sch_frag_rt = { 0 };
                unsigned long orig_dst;

                local_lock_nested_bh(&sch_frag_data_storage.bh_lock);
                sch_frag_prepare_frag(skb, xmit);
                dst_init(&sch_frag_rt.dst, &sch_frag_dst_ops, NULL,
                         DST_OBSOLETE_NONE, DST_NOCOUNT);
                sch_frag_rt.dst.dev = skb->dev;

                orig_dst = skb->_skb_refdst;
                skb_dst_set_noref(skb, &sch_frag_rt.dst);
                IPCB(skb)->frag_max_size = mru;

                ret = ip_do_fragment(net, skb->sk, skb, sch_frag_xmit);
                local_unlock_nested_bh(&sch_frag_data_storage.bh_lock);
                refdst_drop(orig_dst);
        } else if (skb_protocol(skb, true) == htons(ETH_P_IPV6)) {
                unsigned long orig_dst;
                struct rt6_info sch_frag_rt;

                local_lock_nested_bh(&sch_frag_data_storage.bh_lock);
                sch_frag_prepare_frag(skb, xmit);
                memset(&sch_frag_rt, 0, sizeof(sch_frag_rt));
                dst_init(&sch_frag_rt.dst, &sch_frag_dst_ops, NULL,
                         DST_OBSOLETE_NONE, DST_NOCOUNT);
                sch_frag_rt.dst.dev = skb->dev;

                orig_dst = skb->_skb_refdst;
                skb_dst_set_noref(skb, &sch_frag_rt.dst);
                IP6CB(skb)->frag_max_size = mru;

                ret = ipv6_stub->ipv6_fragment(net, skb->sk, skb,
                                               sch_frag_xmit);
                local_unlock_nested_bh(&sch_frag_data_storage.bh_lock);
                refdst_drop(orig_dst);
        } else {
                net_warn_ratelimited("Fail frag %s: eth=%x, MRU=%d, MTU=%d\n",
                                     netdev_name(skb->dev),
                                     ntohs(skb_protocol(skb, true)), mru,
                                     skb->dev->mtu);
                goto err;
        }

        return ret;
err:
        kfree_skb(skb);
        return ret;
}

int sch_frag_xmit_hook(struct sk_buff *skb, int (*xmit)(struct sk_buff *skb))
{
        u16 mru = tc_skb_cb(skb)->mru;
        int err;

        if (mru && skb->len > mru + skb->dev->hard_header_len)
                err = sch_fragment(dev_net(skb->dev), skb, mru, xmit);
        else
                err = xmit(skb);

        return err;
}
EXPORT_SYMBOL_GPL(sch_frag_xmit_hook);