/*
 *      IPV4 GSO/GRO offload support
 *      Linux INET implementation
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *      GRE GSO support
 */

#include <linux/skbuff.h>
#include <linux/init.h>
#include <net/protocol.h>
#include <net/gre.h>

static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
                                       netdev_features_t features)
{
        int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
        struct sk_buff *segs = ERR_PTR(-EINVAL);
        u16 mac_offset = skb->mac_header;
        __be16 protocol = skb->protocol;
        u16 mac_len = skb->mac_len;
        int gre_offset, outer_hlen;
        bool need_csum, ufo, gso_partial;

        if (!skb->encapsulation)
                goto out;

        if (unlikely(tnl_hlen < sizeof(struct gre_base_hdr)))
                goto out;

        if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
                goto out;

        /* setup inner skb. */
        skb->encapsulation = 0;
        SKB_GSO_CB(skb)->encap_level = 0;
        __skb_pull(skb, tnl_hlen);
        skb_reset_mac_header(skb);
        skb_set_network_header(skb, skb_inner_network_offset(skb));
        skb->mac_len = skb_inner_network_offset(skb);
        skb->protocol = skb->inner_protocol;

        need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM);
        skb->encap_hdr_csum = need_csum;

        ufo = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP);

        features &= skb->dev->hw_enc_features;

        /* The only checksum offload we care about from here on out is the
         * outer one so strip the existing checksum feature flags based
         * on the fact that we will be computing our checksum in software.
         */
        if (ufo) {
                features &= ~NETIF_F_CSUM_MASK;
                if (!need_csum)
                        features |= NETIF_F_HW_CSUM;
        }

        /* segment inner packet. */
        segs = skb_mac_gso_segment(skb, features);
        if (IS_ERR_OR_NULL(segs)) {
                skb_gso_error_unwind(skb, protocol, tnl_hlen, mac_offset,
                                     mac_len);
                goto out;
        }

        gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);

        outer_hlen = skb_tnl_header_len(skb);
        gre_offset = outer_hlen - tnl_hlen;
        skb = segs;
        do {
                struct gre_base_hdr *greh;
                __sum16 *pcsum;

                /* Set up inner headers if we are offloading inner checksum */
                if (skb->ip_summed == CHECKSUM_PARTIAL) {
                        skb_reset_inner_headers(skb);
                        skb->encapsulation = 1;
                }

                skb->mac_len = mac_len;
                skb->protocol = protocol;

                __skb_push(skb, outer_hlen);
                skb_reset_mac_header(skb);
                skb_set_network_header(skb, mac_len);
                skb_set_transport_header(skb, gre_offset);

                if (!need_csum)
                        continue;

                greh = (struct gre_base_hdr *)skb_transport_header(skb);
                pcsum = (__sum16 *)(greh + 1);

                if (gso_partial) {
                        unsigned int partial_adj;

                        /* Adjust checksum to account for the fact that
                         * the partial checksum is based on actual size
                         * whereas headers should be based on MSS size.
                         */
                        partial_adj = skb->len + skb_headroom(skb) -
                                      SKB_GSO_CB(skb)->data_offset -
                                      skb_shinfo(skb)->gso_size;
                        *pcsum = ~csum_fold((__force __wsum)htonl(partial_adj));
                } else {
                        *pcsum = 0;
                }

                *(pcsum + 1) = 0;
                *pcsum = gso_make_checksum(skb, 0);
        } while ((skb = skb->next));
out:
        return segs;
}

static struct sk_buff **gre_gro_receive(struct sk_buff **head,
                                        struct sk_buff *skb)
{
        struct sk_buff **pp = NULL;
        struct sk_buff *p;
        const struct gre_base_hdr *greh;
        unsigned int hlen, grehlen;
        unsigned int off;
        int flush = 1;
        struct packet_offload *ptype;
        __be16 type;

        if (NAPI_GRO_CB(skb)->encap_mark)
                goto out;

        NAPI_GRO_CB(skb)->encap_mark = 1;

        off = skb_gro_offset(skb);
        hlen = off + sizeof(*greh);
        greh = skb_gro_header_fast(skb, off);
        if (skb_gro_header_hard(skb, hlen)) {
                greh = skb_gro_header_slow(skb, hlen, off);
                if (unlikely(!greh))
                        goto out;
        }

        /* Only support version 0 and K (key), C (csum) flags. Note that
         * although the support for the S (seq#) flag can be added easily
         * for GRO, this is problematic for GSO hence can not be enabled
         * here because a GRO pkt may end up in the forwarding path, thus
         * requiring GSO support to break it up correctly.
         */
        if ((greh->flags & ~(GRE_KEY|GRE_CSUM)) != 0)
                goto out;

        /* We can only support GRE_CSUM if we can track the location of
         * the GRE header.  In the case of FOU/GUE we cannot because the
         * outer UDP header displaces the GRE header leaving us in a state
         * of limbo.
         */
        if ((greh->flags & GRE_CSUM) && NAPI_GRO_CB(skb)->is_fou)
                goto out;

        type = greh->protocol;

        rcu_read_lock();
        ptype = gro_find_receive_by_type(type);
        if (!ptype)
                goto out_unlock;

        grehlen = GRE_HEADER_SECTION;

        if (greh->flags & GRE_KEY)
                grehlen += GRE_HEADER_SECTION;

        if (greh->flags & GRE_CSUM)
                grehlen += GRE_HEADER_SECTION;

        hlen = off + grehlen;
        if (skb_gro_header_hard(skb, hlen)) {
                greh = skb_gro_header_slow(skb, hlen, off);
                if (unlikely(!greh))
                        goto out_unlock;
        }

        /* Don't bother verifying checksum if we're going to flush anyway. */
        if ((greh->flags & GRE_CSUM) && !NAPI_GRO_CB(skb)->flush) {
                if (skb_gro_checksum_simple_validate(skb))
                        goto out_unlock;

                skb_gro_checksum_try_convert(skb, IPPROTO_GRE, 0,
                                             null_compute_pseudo);
        }

        for (p = *head; p; p = p->next) {
                const struct gre_base_hdr *greh2;

                if (!NAPI_GRO_CB(p)->same_flow)
                        continue;

                /* The following checks are needed to ensure only pkts
                 * from the same tunnel are considered for aggregation.
                 * The criteria for "the same tunnel" includes:
                 * 1) same version (we only support version 0 here)
                 * 2) same protocol (we only support ETH_P_IP for now)
                 * 3) same set of flags
                 * 4) same key if the key field is present.
                 */
                greh2 = (struct gre_base_hdr *)(p->data + off);

                if (greh2->flags != greh->flags ||
                    greh2->protocol != greh->protocol) {
                        NAPI_GRO_CB(p)->same_flow = 0;
                        continue;
                }
                if (greh->flags & GRE_KEY) {
                        /* compare keys */
                        if (*(__be32 *)(greh2+1) != *(__be32 *)(greh+1)) {
                                NAPI_GRO_CB(p)->same_flow = 0;
                                continue;
                        }
                }
        }

        skb_gro_pull(skb, grehlen);

        /* Adjusted NAPI_GRO_CB(skb)->csum after skb_gro_pull()*/
        skb_gro_postpull_rcsum(skb, greh, grehlen);

        pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
        flush = 0;

out_unlock:
        rcu_read_unlock();
out:
        NAPI_GRO_CB(skb)->flush |= flush;

        return pp;
}

static int gre_gro_complete(struct sk_buff *skb, int nhoff)
{
        struct gre_base_hdr *greh = (struct gre_base_hdr *)(skb->data + nhoff);
        struct packet_offload *ptype;
        unsigned int grehlen = sizeof(*greh);
        int err = -ENOENT;
        __be16 type;

        skb->encapsulation = 1;
        skb_shinfo(skb)->gso_type = SKB_GSO_GRE;

        type = greh->protocol;
        if (greh->flags & GRE_KEY)
                grehlen += GRE_HEADER_SECTION;

        if (greh->flags & GRE_CSUM)
                grehlen += GRE_HEADER_SECTION;

        rcu_read_lock();
        ptype = gro_find_complete_by_type(type);
        if (ptype)
                err = ptype->callbacks.gro_complete(skb, nhoff + grehlen);

        rcu_read_unlock();

        skb_set_inner_mac_header(skb, nhoff + grehlen);

        return err;
}

static const struct net_offload gre_offload = {
        .callbacks = {
                .gso_segment = gre_gso_segment,
                .gro_receive = gre_gro_receive,
                .gro_complete = gre_gro_complete,
        },
};

static int __init gre_offload_init(void)
{
        int err;

        err = inet_add_offload(&gre_offload, IPPROTO_GRE);
#if IS_ENABLED(CONFIG_IPV6)
        if (err)
                return err;

        err = inet6_add_offload(&gre_offload, IPPROTO_GRE);
        if (err)
                inet_del_offload(&gre_offload, IPPROTO_GRE);
#endif

        return err;
}
device_initcall(gre_offload_init);