// SPDX-License-Identifier: GPL-2.0-or-later
/* GTP according to GSM TS 09.60 / 3GPP TS 29.060
 *
 * (C) 2012-2014 by sysmocom - s.f.m.c. GmbH
 * (C) 2016 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * Author: Harald Welte <hwelte@sysmocom.de>
 *         Pablo Neira Ayuso <pablo@netfilter.org>
 *         Andreas Schultz <aschultz@travelping.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/udp.h>
#include <linux/rculist.h>
#include <linux/jhash.h>
#include <linux/if_tunnel.h>
#include <linux/net.h>
#include <linux/file.h>
#include <linux/gtp.h>

#include <net/net_namespace.h>
#include <net/protocol.h>
#include <net/ip.h>
#include <net/udp.h>
#include <net/udp_tunnel.h>
#include <net/icmp.h>
#include <net/xfrm.h>
#include <net/genetlink.h>
#include <net/netns/generic.h>
#include <net/gtp.h>

/* An active session for the subscriber. */
struct pdp_ctx {
        struct hlist_node       hlist_tid;
        struct hlist_node       hlist_addr;

        union {
                struct {
                        u64     tid;
                        u16     flow;
                } v0;
                struct {
                        u32     i_tei;
                        u32     o_tei;
                } v1;
        } u;
        u8                      gtp_version;
        u16                     af;

        struct in_addr          ms_addr_ip4;
        struct in_addr          peer_addr_ip4;

        struct sock             *sk;
        struct net_device       *dev;

        atomic_t                tx_seq;
        struct rcu_head         rcu_head;
};

/* One instance of the GTP device. */
struct gtp_dev {
        struct list_head        list;

        struct sock             *sk0;
        struct sock             *sk1u;
        u8                      sk_created;

        struct net_device       *dev;
        struct net              *net;

        unsigned int            role;
        unsigned int            hash_size;
        struct hlist_head       *tid_hash;
        struct hlist_head       *addr_hash;

        u8                      restart_count;
};

struct echo_info {
        struct in_addr          ms_addr_ip4;
        struct in_addr          peer_addr_ip4;
        u8                      gtp_version;
};

static unsigned int gtp_net_id __read_mostly;

struct gtp_net {
        struct list_head gtp_dev_list;
};

static u32 gtp_h_initval;

static struct genl_family gtp_genl_family;

enum gtp_multicast_groups {
        GTP_GENL_MCGRP,
};

static const struct genl_multicast_group gtp_genl_mcgrps[] = {
        [GTP_GENL_MCGRP] = { .name = GTP_GENL_MCGRP_NAME },
};

static void pdp_context_delete(struct pdp_ctx *pctx);

static inline u32 gtp0_hashfn(u64 tid)
{
        u32 *tid32 = (u32 *) &tid;
        return jhash_2words(tid32[0], tid32[1], gtp_h_initval);
}

static inline u32 gtp1u_hashfn(u32 tid)
{
        return jhash_1word(tid, gtp_h_initval);
}

static inline u32 ipv4_hashfn(__be32 ip)
{
        return jhash_1word((__force u32)ip, gtp_h_initval);
}

/* Resolve a PDP context structure based on the 64bit TID. */
static struct pdp_ctx *gtp0_pdp_find(struct gtp_dev *gtp, u64 tid)
{
        struct hlist_head *head;
        struct pdp_ctx *pdp;

        head = &gtp->tid_hash[gtp0_hashfn(tid) % gtp->hash_size];

        hlist_for_each_entry_rcu(pdp, head, hlist_tid) {
                if (pdp->gtp_version == GTP_V0 &&
                    pdp->u.v0.tid == tid)
                        return pdp;
        }
        return NULL;
}

/* Resolve a PDP context structure based on the 32bit TEI. */
static struct pdp_ctx *gtp1_pdp_find(struct gtp_dev *gtp, u32 tid)
{
        struct hlist_head *head;
        struct pdp_ctx *pdp;

        head = &gtp->tid_hash[gtp1u_hashfn(tid) % gtp->hash_size];

        hlist_for_each_entry_rcu(pdp, head, hlist_tid) {
                if (pdp->gtp_version == GTP_V1 &&
                    pdp->u.v1.i_tei == tid)
                        return pdp;
        }
        return NULL;
}

/* Resolve a PDP context based on IPv4 address of MS. */
static struct pdp_ctx *ipv4_pdp_find(struct gtp_dev *gtp, __be32 ms_addr)
{
        struct hlist_head *head;
        struct pdp_ctx *pdp;

        head = &gtp->addr_hash[ipv4_hashfn(ms_addr) % gtp->hash_size];

        hlist_for_each_entry_rcu(pdp, head, hlist_addr) {
                if (pdp->af == AF_INET &&
                    pdp->ms_addr_ip4.s_addr == ms_addr)
                        return pdp;
        }

        return NULL;
}

static bool gtp_check_ms_ipv4(struct sk_buff *skb, struct pdp_ctx *pctx,
                                  unsigned int hdrlen, unsigned int role)
{
        struct iphdr *iph;

        if (!pskb_may_pull(skb, hdrlen + sizeof(struct iphdr)))
                return false;

        iph = (struct iphdr *)(skb->data + hdrlen);

        if (role == GTP_ROLE_SGSN)
                return iph->daddr == pctx->ms_addr_ip4.s_addr;
        else
                return iph->saddr == pctx->ms_addr_ip4.s_addr;
}

/* Check if the inner IP address in this packet is assigned to any
 * existing mobile subscriber.
 */
static bool gtp_check_ms(struct sk_buff *skb, struct pdp_ctx *pctx,
                             unsigned int hdrlen, unsigned int role)
{
        switch (ntohs(skb->protocol)) {
        case ETH_P_IP:
                return gtp_check_ms_ipv4(skb, pctx, hdrlen, role);
        }
        return false;
}

static int gtp_rx(struct pdp_ctx *pctx, struct sk_buff *skb,
                        unsigned int hdrlen, unsigned int role)
{
        if (!gtp_check_ms(skb, pctx, hdrlen, role)) {
                netdev_dbg(pctx->dev, "No PDP ctx for this MS\n");
                return 1;
        }

        /* Get rid of the GTP + UDP headers. */
        if (iptunnel_pull_header(skb, hdrlen, skb->protocol,
                         !net_eq(sock_net(pctx->sk), dev_net(pctx->dev)))) {
                pctx->dev->stats.rx_length_errors++;
                goto err;
        }

        netdev_dbg(pctx->dev, "forwarding packet from GGSN to uplink\n");

        /* Now that the UDP and the GTP header have been removed, set up the
         * new network header. This is required by the upper layer to
         * calculate the transport header.
         */
        skb_reset_network_header(skb);
        skb_reset_mac_header(skb);

        skb->dev = pctx->dev;

        dev_sw_netstats_rx_add(pctx->dev, skb->len);

        __netif_rx(skb);
        return 0;

err:
        pctx->dev->stats.rx_dropped++;
        return -1;
}

static struct rtable *ip4_route_output_gtp(struct flowi4 *fl4,
                                           const struct sock *sk,
                                           __be32 daddr, __be32 saddr)
{
        memset(fl4, 0, sizeof(*fl4));
        fl4->flowi4_oif         = sk->sk_bound_dev_if;
        fl4->daddr              = daddr;
        fl4->saddr              = saddr;
        fl4->flowi4_tos         = RT_CONN_FLAGS(sk);
        fl4->flowi4_proto       = sk->sk_protocol;

        return ip_route_output_key(sock_net(sk), fl4);
}

/* GSM TS 09.60. 7.3
 * In all Path Management messages:
 * - TID: is not used and shall be set to 0.
 * - Flow Label is not used and shall be set to 0
 * In signalling messages:
 * - number: this field is not yet used in signalling messages.
 *   It shall be set to 255 by the sender and shall be ignored
 *   by the receiver
 * Returns true if the echo req was correct, false otherwise.
 */
static bool gtp0_validate_echo_hdr(struct gtp0_header *gtp0)
{
        return !(gtp0->tid || (gtp0->flags ^ 0x1e) ||
                gtp0->number != 0xff || gtp0->flow);
}

/* msg_type has to be GTP_ECHO_REQ or GTP_ECHO_RSP */
static void gtp0_build_echo_msg(struct gtp0_header *hdr, __u8 msg_type)
{
        int len_pkt, len_hdr;

        hdr->flags = 0x1e; /* v0, GTP-non-prime. */
        hdr->type = msg_type;
        /* GSM TS 09.60. 7.3 In all Path Management Flow Label and TID
         * are not used and shall be set to 0.
         */
        hdr->flow = 0;
        hdr->tid = 0;
        hdr->number = 0xff;
        hdr->spare[0] = 0xff;
        hdr->spare[1] = 0xff;
        hdr->spare[2] = 0xff;

        len_pkt = sizeof(struct gtp0_packet);
        len_hdr = sizeof(struct gtp0_header);

        if (msg_type == GTP_ECHO_RSP)
                hdr->length = htons(len_pkt - len_hdr);
        else
                hdr->length = 0;
}

static int gtp0_send_echo_resp(struct gtp_dev *gtp, struct sk_buff *skb)
{
        struct gtp0_packet *gtp_pkt;
        struct gtp0_header *gtp0;
        struct rtable *rt;
        struct flowi4 fl4;
        struct iphdr *iph;
        __be16 seq;

        gtp0 = (struct gtp0_header *)(skb->data + sizeof(struct udphdr));

        if (!gtp0_validate_echo_hdr(gtp0))
                return -1;

        seq = gtp0->seq;

        /* pull GTP and UDP headers */
        skb_pull_data(skb, sizeof(struct gtp0_header) + sizeof(struct udphdr));

        gtp_pkt = skb_push(skb, sizeof(struct gtp0_packet));
        memset(gtp_pkt, 0, sizeof(struct gtp0_packet));

        gtp0_build_echo_msg(&gtp_pkt->gtp0_h, GTP_ECHO_RSP);

        /* GSM TS 09.60. 7.3 The Sequence Number in a signalling response
         * message shall be copied from the signalling request message
         * that the GSN is replying to.
         */
        gtp_pkt->gtp0_h.seq = seq;

        gtp_pkt->ie.tag = GTPIE_RECOVERY;
        gtp_pkt->ie.val = gtp->restart_count;

        iph = ip_hdr(skb);

        /* find route to the sender,
         * src address becomes dst address and vice versa.
         */
        rt = ip4_route_output_gtp(&fl4, gtp->sk0, iph->saddr, iph->daddr);
        if (IS_ERR(rt)) {
                netdev_dbg(gtp->dev, "no route for echo response from %pI4\n",
                           &iph->saddr);
                return -1;
        }

        udp_tunnel_xmit_skb(rt, gtp->sk0, skb,
                            fl4.saddr, fl4.daddr,
                            iph->tos,
                            ip4_dst_hoplimit(&rt->dst),
                            0,
                            htons(GTP0_PORT), htons(GTP0_PORT),
                            !net_eq(sock_net(gtp->sk1u),
                                    dev_net(gtp->dev)),
                            false);
        return 0;
}

static int gtp_genl_fill_echo(struct sk_buff *skb, u32 snd_portid, u32 snd_seq,
                              int flags, u32 type, struct echo_info echo)
{
        void *genlh;

        genlh = genlmsg_put(skb, snd_portid, snd_seq, &gtp_genl_family, flags,
                            type);
        if (!genlh)
                goto failure;

        if (nla_put_u32(skb, GTPA_VERSION, echo.gtp_version) ||
            nla_put_be32(skb, GTPA_PEER_ADDRESS, echo.peer_addr_ip4.s_addr) ||
            nla_put_be32(skb, GTPA_MS_ADDRESS, echo.ms_addr_ip4.s_addr))
                goto failure;

        genlmsg_end(skb, genlh);
        return 0;

failure:
        genlmsg_cancel(skb, genlh);
        return -EMSGSIZE;
}

static int gtp0_handle_echo_resp(struct gtp_dev *gtp, struct sk_buff *skb)
{
        struct gtp0_header *gtp0;
        struct echo_info echo;
        struct sk_buff *msg;
        struct iphdr *iph;
        int ret;

        gtp0 = (struct gtp0_header *)(skb->data + sizeof(struct udphdr));

        if (!gtp0_validate_echo_hdr(gtp0))
                return -1;

        iph = ip_hdr(skb);
        echo.ms_addr_ip4.s_addr = iph->daddr;
        echo.peer_addr_ip4.s_addr = iph->saddr;
        echo.gtp_version = GTP_V0;

        msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
        if (!msg)
                return -ENOMEM;

        ret = gtp_genl_fill_echo(msg, 0, 0, 0, GTP_CMD_ECHOREQ, echo);
        if (ret < 0) {
                nlmsg_free(msg);
                return ret;
        }

        return genlmsg_multicast_netns(&gtp_genl_family, dev_net(gtp->dev),
                                       msg, 0, GTP_GENL_MCGRP, GFP_ATOMIC);
}

/* 1 means pass up to the stack, -1 means drop and 0 means decapsulated. */
static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
{
        unsigned int hdrlen = sizeof(struct udphdr) +
                              sizeof(struct gtp0_header);
        struct gtp0_header *gtp0;
        struct pdp_ctx *pctx;

        if (!pskb_may_pull(skb, hdrlen))
                return -1;

        gtp0 = (struct gtp0_header *)(skb->data + sizeof(struct udphdr));

        if ((gtp0->flags >> 5) != GTP_V0)
                return 1;

        /* If the sockets were created in kernel, it means that
         * there is no daemon running in userspace which would
         * handle echo request.
         */
        if (gtp0->type == GTP_ECHO_REQ && gtp->sk_created)
                return gtp0_send_echo_resp(gtp, skb);

        if (gtp0->type == GTP_ECHO_RSP && gtp->sk_created)
                return gtp0_handle_echo_resp(gtp, skb);

        if (gtp0->type != GTP_TPDU)
                return 1;

        pctx = gtp0_pdp_find(gtp, be64_to_cpu(gtp0->tid));
        if (!pctx) {
                netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
                return 1;
        }

        return gtp_rx(pctx, skb, hdrlen, gtp->role);
}

/* msg_type has to be GTP_ECHO_REQ or GTP_ECHO_RSP */
static void gtp1u_build_echo_msg(struct gtp1_header_long *hdr, __u8 msg_type)
{
        int len_pkt, len_hdr;

        /* S flag must be set to 1 */
        hdr->flags = 0x32; /* v1, GTP-non-prime. */
        hdr->type = msg_type;
        /* 3GPP TS 29.281 5.1 - TEID has to be set to 0 */
        hdr->tid = 0;

        /* seq, npdu and next should be counted to the length of the GTP packet
         * that's why szie of gtp1_header should be subtracted,
         * not size of gtp1_header_long.
         */

        len_hdr = sizeof(struct gtp1_header);

        if (msg_type == GTP_ECHO_RSP) {
                len_pkt = sizeof(struct gtp1u_packet);
                hdr->length = htons(len_pkt - len_hdr);
        } else {
                /* GTP_ECHO_REQ does not carry GTP Information Element,
                 * the why gtp1_header_long is used here.
                 */
                len_pkt = sizeof(struct gtp1_header_long);
                hdr->length = htons(len_pkt - len_hdr);
        }
}

static int gtp1u_send_echo_resp(struct gtp_dev *gtp, struct sk_buff *skb)
{
        struct gtp1_header_long *gtp1u;
        struct gtp1u_packet *gtp_pkt;
        struct rtable *rt;
        struct flowi4 fl4;
        struct iphdr *iph;

        gtp1u = (struct gtp1_header_long *)(skb->data + sizeof(struct udphdr));

        /* 3GPP TS 29.281 5.1 - For the Echo Request, Echo Response,
         * Error Indication and Supported Extension Headers Notification
         * messages, the S flag shall be set to 1 and TEID shall be set to 0.
         */
        if (!(gtp1u->flags & GTP1_F_SEQ) || gtp1u->tid)
                return -1;

        /* pull GTP and UDP headers */
        skb_pull_data(skb,
                      sizeof(struct gtp1_header_long) + sizeof(struct udphdr));

        gtp_pkt = skb_push(skb, sizeof(struct gtp1u_packet));
        memset(gtp_pkt, 0, sizeof(struct gtp1u_packet));

        gtp1u_build_echo_msg(&gtp_pkt->gtp1u_h, GTP_ECHO_RSP);

        /* 3GPP TS 29.281 7.7.2 - The Restart Counter value in the
         * Recovery information element shall not be used, i.e. it shall
         * be set to zero by the sender and shall be ignored by the receiver.
         * The Recovery information element is mandatory due to backwards
         * compatibility reasons.
         */
        gtp_pkt->ie.tag = GTPIE_RECOVERY;
        gtp_pkt->ie.val = 0;

        iph = ip_hdr(skb);

        /* find route to the sender,
         * src address becomes dst address and vice versa.
         */
        rt = ip4_route_output_gtp(&fl4, gtp->sk1u, iph->saddr, iph->daddr);
        if (IS_ERR(rt)) {
                netdev_dbg(gtp->dev, "no route for echo response from %pI4\n",
                           &iph->saddr);
                return -1;
        }

        udp_tunnel_xmit_skb(rt, gtp->sk1u, skb,
                            fl4.saddr, fl4.daddr,
                            iph->tos,
                            ip4_dst_hoplimit(&rt->dst),
                            0,
                            htons(GTP1U_PORT), htons(GTP1U_PORT),
                            !net_eq(sock_net(gtp->sk1u),
                                    dev_net(gtp->dev)),
                            false);
        return 0;
}

static int gtp1u_handle_echo_resp(struct gtp_dev *gtp, struct sk_buff *skb)
{
        struct gtp1_header_long *gtp1u;
        struct echo_info echo;
        struct sk_buff *msg;
        struct iphdr *iph;
        int ret;

        gtp1u = (struct gtp1_header_long *)(skb->data + sizeof(struct udphdr));

        /* 3GPP TS 29.281 5.1 - For the Echo Request, Echo Response,
         * Error Indication and Supported Extension Headers Notification
         * messages, the S flag shall be set to 1 and TEID shall be set to 0.
         */
        if (!(gtp1u->flags & GTP1_F_SEQ) || gtp1u->tid)
                return -1;

        iph = ip_hdr(skb);
        echo.ms_addr_ip4.s_addr = iph->daddr;
        echo.peer_addr_ip4.s_addr = iph->saddr;
        echo.gtp_version = GTP_V1;

        msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
        if (!msg)
                return -ENOMEM;

        ret = gtp_genl_fill_echo(msg, 0, 0, 0, GTP_CMD_ECHOREQ, echo);
        if (ret < 0) {
                nlmsg_free(msg);
                return ret;
        }

        return genlmsg_multicast_netns(&gtp_genl_family, dev_net(gtp->dev),
                                       msg, 0, GTP_GENL_MCGRP, GFP_ATOMIC);
}

static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
{
        unsigned int hdrlen = sizeof(struct udphdr) +
                              sizeof(struct gtp1_header);
        struct gtp1_header *gtp1;
        struct pdp_ctx *pctx;

        if (!pskb_may_pull(skb, hdrlen))
                return -1;

        gtp1 = (struct gtp1_header *)(skb->data + sizeof(struct udphdr));

        if ((gtp1->flags >> 5) != GTP_V1)
                return 1;

        /* If the sockets were created in kernel, it means that
         * there is no daemon running in userspace which would
         * handle echo request.
         */
        if (gtp1->type == GTP_ECHO_REQ && gtp->sk_created)
                return gtp1u_send_echo_resp(gtp, skb);

        if (gtp1->type == GTP_ECHO_RSP && gtp->sk_created)
                return gtp1u_handle_echo_resp(gtp, skb);

        if (gtp1->type != GTP_TPDU)
                return 1;

        /* From 29.060: "This field shall be present if and only if any one or
         * more of the S, PN and E flags are set.".
         *
         * If any of the bit is set, then the remaining ones also have to be
         * set.
         */
        if (gtp1->flags & GTP1_F_MASK)
                hdrlen += 4;

        /* Make sure the header is larger enough, including extensions. */
        if (!pskb_may_pull(skb, hdrlen))
                return -1;

        gtp1 = (struct gtp1_header *)(skb->data + sizeof(struct udphdr));

        pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid));
        if (!pctx) {
                netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
                return 1;
        }

        return gtp_rx(pctx, skb, hdrlen, gtp->role);
}

static void __gtp_encap_destroy(struct sock *sk)
{
        struct gtp_dev *gtp;

        lock_sock(sk);
        gtp = sk->sk_user_data;
        if (gtp) {
                if (gtp->sk0 == sk)
                        gtp->sk0 = NULL;
                else
                        gtp->sk1u = NULL;
                udp_sk(sk)->encap_type = 0;
                rcu_assign_sk_user_data(sk, NULL);
                sock_put(sk);
        }
        release_sock(sk);
}

static void gtp_encap_destroy(struct sock *sk)
{
        rtnl_lock();
        __gtp_encap_destroy(sk);
        rtnl_unlock();
}

static void gtp_encap_disable_sock(struct sock *sk)
{
        if (!sk)
                return;

        __gtp_encap_destroy(sk);
}

static void gtp_encap_disable(struct gtp_dev *gtp)
{
        if (gtp->sk_created) {
                udp_tunnel_sock_release(gtp->sk0->sk_socket);
                udp_tunnel_sock_release(gtp->sk1u->sk_socket);
                gtp->sk_created = false;
                gtp->sk0 = NULL;
                gtp->sk1u = NULL;
        } else {
                gtp_encap_disable_sock(gtp->sk0);
                gtp_encap_disable_sock(gtp->sk1u);
        }
}

/* UDP encapsulation receive handler. See net/ipv4/udp.c.
 * Return codes: 0: success, <0: error, >0: pass up to userspace UDP socket.
 */
static int gtp_encap_recv(struct sock *sk, struct sk_buff *skb)
{
        struct gtp_dev *gtp;
        int ret = 0;

        gtp = rcu_dereference_sk_user_data(sk);
        if (!gtp)
                return 1;

        netdev_dbg(gtp->dev, "encap_recv sk=%p\n", sk);

        switch (udp_sk(sk)->encap_type) {
        case UDP_ENCAP_GTP0:
                netdev_dbg(gtp->dev, "received GTP0 packet\n");
                ret = gtp0_udp_encap_recv(gtp, skb);
                break;
        case UDP_ENCAP_GTP1U:
                netdev_dbg(gtp->dev, "received GTP1U packet\n");
                ret = gtp1u_udp_encap_recv(gtp, skb);
                break;
        default:
                ret = -1; /* Shouldn't happen. */
        }

        switch (ret) {
        case 1:
                netdev_dbg(gtp->dev, "pass up to the process\n");
                break;
        case 0:
                break;
        case -1:
                netdev_dbg(gtp->dev, "GTP packet has been dropped\n");
                kfree_skb(skb);
                ret = 0;
                break;
        }

        return ret;
}

static int gtp_dev_init(struct net_device *dev)
{
        struct gtp_dev *gtp = netdev_priv(dev);

        gtp->dev = dev;

        dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
        if (!dev->tstats)
                return -ENOMEM;

        return 0;
}

static void gtp_dev_uninit(struct net_device *dev)
{
        struct gtp_dev *gtp = netdev_priv(dev);

        gtp_encap_disable(gtp);
        free_percpu(dev->tstats);
}

static inline void gtp0_push_header(struct sk_buff *skb, struct pdp_ctx *pctx)
{
        int payload_len = skb->len;
        struct gtp0_header *gtp0;

        gtp0 = skb_push(skb, sizeof(*gtp0));

        gtp0->flags     = 0x1e; /* v0, GTP-non-prime. */
        gtp0->type      = GTP_TPDU;
        gtp0->length    = htons(payload_len);
        gtp0->seq       = htons((atomic_inc_return(&pctx->tx_seq) - 1) % 0xffff);
        gtp0->flow      = htons(pctx->u.v0.flow);
        gtp0->number    = 0xff;
        gtp0->spare[0]  = gtp0->spare[1] = gtp0->spare[2] = 0xff;
        gtp0->tid       = cpu_to_be64(pctx->u.v0.tid);
}

static inline void gtp1_push_header(struct sk_buff *skb, struct pdp_ctx *pctx)
{
        int payload_len = skb->len;
        struct gtp1_header *gtp1;

        gtp1 = skb_push(skb, sizeof(*gtp1));

        /* Bits    8  7  6  5  4  3  2  1
         *        +--+--+--+--+--+--+--+--+
         *        |version |PT| 0| E| S|PN|
         *        +--+--+--+--+--+--+--+--+
         *          0  0  1  1  1  0  0  0
         */
        gtp1->flags     = 0x30; /* v1, GTP-non-prime. */
        gtp1->type      = GTP_TPDU;
        gtp1->length    = htons(payload_len);
        gtp1->tid       = htonl(pctx->u.v1.o_tei);

        /* TODO: Support for extension header, sequence number and N-PDU.
         *       Update the length field if any of them is available.
         */
}

struct gtp_pktinfo {
        struct sock             *sk;
        struct iphdr            *iph;
        struct flowi4           fl4;
        struct rtable           *rt;
        struct pdp_ctx          *pctx;
        struct net_device       *dev;
        __be16                  gtph_port;
};

static void gtp_push_header(struct sk_buff *skb, struct gtp_pktinfo *pktinfo)
{
        switch (pktinfo->pctx->gtp_version) {
        case GTP_V0:
                pktinfo->gtph_port = htons(GTP0_PORT);
                gtp0_push_header(skb, pktinfo->pctx);
                break;
        case GTP_V1:
                pktinfo->gtph_port = htons(GTP1U_PORT);
                gtp1_push_header(skb, pktinfo->pctx);
                break;
        }
}

static inline void gtp_set_pktinfo_ipv4(struct gtp_pktinfo *pktinfo,
                                        struct sock *sk, struct iphdr *iph,
                                        struct pdp_ctx *pctx, struct rtable *rt,
                                        struct flowi4 *fl4,
                                        struct net_device *dev)
{
        pktinfo->sk     = sk;
        pktinfo->iph    = iph;
        pktinfo->pctx   = pctx;
        pktinfo->rt     = rt;
        pktinfo->fl4    = *fl4;
        pktinfo->dev    = dev;
}

static int gtp_build_skb_ip4(struct sk_buff *skb, struct net_device *dev,
                             struct gtp_pktinfo *pktinfo)
{
        struct gtp_dev *gtp = netdev_priv(dev);
        struct pdp_ctx *pctx;
        struct rtable *rt;
        struct flowi4 fl4;
        struct iphdr *iph;
        __be16 df;
        int mtu;

        /* Read the IP destination address and resolve the PDP context.
         * Prepend PDP header with TEI/TID from PDP ctx.
         */
        iph = ip_hdr(skb);
        if (gtp->role == GTP_ROLE_SGSN)
                pctx = ipv4_pdp_find(gtp, iph->saddr);
        else
                pctx = ipv4_pdp_find(gtp, iph->daddr);

        if (!pctx) {
                netdev_dbg(dev, "no PDP ctx found for %pI4, skip\n",
                           &iph->daddr);
                return -ENOENT;
        }
        netdev_dbg(dev, "found PDP context %p\n", pctx);

        rt = ip4_route_output_gtp(&fl4, pctx->sk, pctx->peer_addr_ip4.s_addr,
                                  inet_sk(pctx->sk)->inet_saddr);
        if (IS_ERR(rt)) {
                netdev_dbg(dev, "no route to SSGN %pI4\n",
                           &pctx->peer_addr_ip4.s_addr);
                dev->stats.tx_carrier_errors++;
                goto err;
        }

        if (rt->dst.dev == dev) {
                netdev_dbg(dev, "circular route to SSGN %pI4\n",
                           &pctx->peer_addr_ip4.s_addr);
                dev->stats.collisions++;
                goto err_rt;
        }

        /* This is similar to tnl_update_pmtu(). */
        df = iph->frag_off;
        if (df) {
                mtu = dst_mtu(&rt->dst) - dev->hard_header_len -
                        sizeof(struct iphdr) - sizeof(struct udphdr);
                switch (pctx->gtp_version) {
                case GTP_V0:
                        mtu -= sizeof(struct gtp0_header);
                        break;
                case GTP_V1:
                        mtu -= sizeof(struct gtp1_header);
                        break;
                }
        } else {
                mtu = dst_mtu(&rt->dst);
        }

        skb_dst_update_pmtu_no_confirm(skb, mtu);

        if (!skb_is_gso(skb) && (iph->frag_off & htons(IP_DF)) &&
            mtu < ntohs(iph->tot_len)) {
                netdev_dbg(dev, "packet too big, fragmentation needed\n");
                icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                              htonl(mtu));
                goto err_rt;
        }

        gtp_set_pktinfo_ipv4(pktinfo, pctx->sk, iph, pctx, rt, &fl4, dev);
        gtp_push_header(skb, pktinfo);

        return 0;
err_rt:
        ip_rt_put(rt);
err:
        return -EBADMSG;
}

static netdev_tx_t gtp_dev_xmit(struct sk_buff *skb, struct net_device *dev)
{
        unsigned int proto = ntohs(skb->protocol);
        struct gtp_pktinfo pktinfo;
        int err;

        /* Ensure there is sufficient headroom. */
        if (skb_cow_head(skb, dev->needed_headroom))
                goto tx_err;

        skb_reset_inner_headers(skb);

        /* PDP context lookups in gtp_build_skb_*() need rcu read-side lock. */
        rcu_read_lock();
        switch (proto) {
        case ETH_P_IP:
                err = gtp_build_skb_ip4(skb, dev, &pktinfo);
                break;
        default:
                err = -EOPNOTSUPP;
                break;
        }
        rcu_read_unlock();

        if (err < 0)
                goto tx_err;

        switch (proto) {
        case ETH_P_IP:
                netdev_dbg(pktinfo.dev, "gtp -> IP src: %pI4 dst: %pI4\n",
                           &pktinfo.iph->saddr, &pktinfo.iph->daddr);
                udp_tunnel_xmit_skb(pktinfo.rt, pktinfo.sk, skb,
                                    pktinfo.fl4.saddr, pktinfo.fl4.daddr,
                                    pktinfo.iph->tos,
                                    ip4_dst_hoplimit(&pktinfo.rt->dst),
                                    0,
                                    pktinfo.gtph_port, pktinfo.gtph_port,
                                    !net_eq(sock_net(pktinfo.pctx->sk),
                                            dev_net(dev)),
                                    false);
                break;
        }

        return NETDEV_TX_OK;
tx_err:
        dev->stats.tx_errors++;
        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}

static const struct net_device_ops gtp_netdev_ops = {
        .ndo_init               = gtp_dev_init,
        .ndo_uninit             = gtp_dev_uninit,
        .ndo_start_xmit         = gtp_dev_xmit,
        .ndo_get_stats64        = dev_get_tstats64,
};

static const struct device_type gtp_type = {
        .name = "gtp",
};

static void gtp_link_setup(struct net_device *dev)
{
        unsigned int max_gtp_header_len = sizeof(struct iphdr) +
                                          sizeof(struct udphdr) +
                                          sizeof(struct gtp0_header);

        dev->netdev_ops         = &gtp_netdev_ops;
        dev->needs_free_netdev  = true;
        SET_NETDEV_DEVTYPE(dev, &gtp_type);

        dev->hard_header_len = 0;
        dev->addr_len = 0;
        dev->mtu = ETH_DATA_LEN - max_gtp_header_len;

        /* Zero header length. */
        dev->type = ARPHRD_NONE;
        dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;

        dev->priv_flags |= IFF_NO_QUEUE;
        dev->features   |= NETIF_F_LLTX;
        netif_keep_dst(dev);

        dev->needed_headroom    = LL_MAX_HEADER + max_gtp_header_len;
}

static int gtp_hashtable_new(struct gtp_dev *gtp, int hsize);
static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[]);

static void gtp_destructor(struct net_device *dev)
{
        struct gtp_dev *gtp = netdev_priv(dev);

        kfree(gtp->addr_hash);
        kfree(gtp->tid_hash);
}

static struct sock *gtp_create_sock(int type, struct gtp_dev *gtp)
{
        struct udp_tunnel_sock_cfg tuncfg = {};
        struct udp_port_cfg udp_conf = {
                .local_ip.s_addr        = htonl(INADDR_ANY),
                .family                 = AF_INET,
        };
        struct net *net = gtp->net;
        struct socket *sock;
        int err;

        if (type == UDP_ENCAP_GTP0)
                udp_conf.local_udp_port = htons(GTP0_PORT);
        else if (type == UDP_ENCAP_GTP1U)

                udp_conf.local_udp_port = htons(GTP1U_PORT);
        else
                return ERR_PTR(-EINVAL);

        err = udp_sock_create(net, &udp_conf, &sock);
        if (err)
                return ERR_PTR(err);

        tuncfg.sk_user_data = gtp;
        tuncfg.encap_type = type;
        tuncfg.encap_rcv = gtp_encap_recv;
        tuncfg.encap_destroy = NULL;

        setup_udp_tunnel_sock(net, sock, &tuncfg);

        return sock->sk;
}

static int gtp_create_sockets(struct gtp_dev *gtp, struct nlattr *data[])
{
        struct sock *sk1u = NULL;
        struct sock *sk0 = NULL;

        sk0 = gtp_create_sock(UDP_ENCAP_GTP0, gtp);
        if (IS_ERR(sk0))
                return PTR_ERR(sk0);

        sk1u = gtp_create_sock(UDP_ENCAP_GTP1U, gtp);
        if (IS_ERR(sk1u)) {
                udp_tunnel_sock_release(sk0->sk_socket);
                return PTR_ERR(sk1u);
        }

        gtp->sk_created = true;
        gtp->sk0 = sk0;
        gtp->sk1u = sk1u;

        return 0;
}

static int gtp_newlink(struct net *src_net, struct net_device *dev,
                       struct nlattr *tb[], struct nlattr *data[],
                       struct netlink_ext_ack *extack)
{
        unsigned int role = GTP_ROLE_GGSN;
        struct gtp_dev *gtp;
        struct gtp_net *gn;
        int hashsize, err;

        gtp = netdev_priv(dev);

        if (!data[IFLA_GTP_PDP_HASHSIZE]) {
                hashsize = 1024;
        } else {
                hashsize = nla_get_u32(data[IFLA_GTP_PDP_HASHSIZE]);
                if (!hashsize)
                        hashsize = 1024;
        }

        if (data[IFLA_GTP_ROLE]) {
                role = nla_get_u32(data[IFLA_GTP_ROLE]);
                if (role > GTP_ROLE_SGSN)
                        return -EINVAL;
        }
        gtp->role = role;

        if (!data[IFLA_GTP_RESTART_COUNT])
                gtp->restart_count = 0;
        else
                gtp->restart_count = nla_get_u8(data[IFLA_GTP_RESTART_COUNT]);

        gtp->net = src_net;

        err = gtp_hashtable_new(gtp, hashsize);
        if (err < 0)
                return err;

        if (data[IFLA_GTP_CREATE_SOCKETS])
                err = gtp_create_sockets(gtp, data);
        else
                err = gtp_encap_enable(gtp, data);
        if (err < 0)
                goto out_hashtable;

        err = register_netdevice(dev);
        if (err < 0) {
                netdev_dbg(dev, "failed to register new netdev %d\n", err);
                goto out_encap;
        }

        gn = net_generic(dev_net(dev), gtp_net_id);
        list_add_rcu(&gtp->list, &gn->gtp_dev_list);
        dev->priv_destructor = gtp_destructor;

        netdev_dbg(dev, "registered new GTP interface\n");

        return 0;

out_encap:
        gtp_encap_disable(gtp);
out_hashtable:
        kfree(gtp->addr_hash);
        kfree(gtp->tid_hash);
        return err;
}

static void gtp_dellink(struct net_device *dev, struct list_head *head)
{
        struct gtp_dev *gtp = netdev_priv(dev);
        struct pdp_ctx *pctx;
        int i;

        for (i = 0; i < gtp->hash_size; i++)
                hlist_for_each_entry_rcu(pctx, &gtp->tid_hash[i], hlist_tid)
                        pdp_context_delete(pctx);

        list_del_rcu(&gtp->list);
        unregister_netdevice_queue(dev, head);
}

static const struct nla_policy gtp_policy[IFLA_GTP_MAX + 1] = {
        [IFLA_GTP_FD0]                  = { .type = NLA_U32 },
        [IFLA_GTP_FD1]                  = { .type = NLA_U32 },
        [IFLA_GTP_PDP_HASHSIZE]         = { .type = NLA_U32 },
        [IFLA_GTP_ROLE]                 = { .type = NLA_U32 },
        [IFLA_GTP_CREATE_SOCKETS]       = { .type = NLA_U8 },
        [IFLA_GTP_RESTART_COUNT]        = { .type = NLA_U8 },
};

static int gtp_validate(struct nlattr *tb[], struct nlattr *data[],
                        struct netlink_ext_ack *extack)
{
        if (!data)
                return -EINVAL;

        return 0;
}

static size_t gtp_get_size(const struct net_device *dev)
{
        return nla_total_size(sizeof(__u32)) + /* IFLA_GTP_PDP_HASHSIZE */
                nla_total_size(sizeof(__u32)) + /* IFLA_GTP_ROLE */
                nla_total_size(sizeof(__u8)); /* IFLA_GTP_RESTART_COUNT */
}

static int gtp_fill_info(struct sk_buff *skb, const struct net_device *dev)
{
        struct gtp_dev *gtp = netdev_priv(dev);

        if (nla_put_u32(skb, IFLA_GTP_PDP_HASHSIZE, gtp->hash_size))
                goto nla_put_failure;
        if (nla_put_u32(skb, IFLA_GTP_ROLE, gtp->role))
                goto nla_put_failure;
        if (nla_put_u8(skb, IFLA_GTP_RESTART_COUNT, gtp->restart_count))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -EMSGSIZE;
}

static struct rtnl_link_ops gtp_link_ops __read_mostly = {
        .kind           = "gtp",
        .maxtype        = IFLA_GTP_MAX,
        .policy         = gtp_policy,
        .priv_size      = sizeof(struct gtp_dev),
        .setup          = gtp_link_setup,
        .validate       = gtp_validate,
        .newlink        = gtp_newlink,
        .dellink        = gtp_dellink,
        .get_size       = gtp_get_size,
        .fill_info      = gtp_fill_info,
};

static int gtp_hashtable_new(struct gtp_dev *gtp, int hsize)
{
        int i;

        gtp->addr_hash = kmalloc_array(hsize, sizeof(struct hlist_head),
                                       GFP_KERNEL | __GFP_NOWARN);
        if (gtp->addr_hash == NULL)
                return -ENOMEM;

        gtp->tid_hash = kmalloc_array(hsize, sizeof(struct hlist_head),
                                      GFP_KERNEL | __GFP_NOWARN);
        if (gtp->tid_hash == NULL)
                goto err1;

        gtp->hash_size = hsize;

        for (i = 0; i < hsize; i++) {
                INIT_HLIST_HEAD(&gtp->addr_hash[i]);
                INIT_HLIST_HEAD(&gtp->tid_hash[i]);
        }
        return 0;
err1:
        kfree(gtp->addr_hash);
        return -ENOMEM;
}

static struct sock *gtp_encap_enable_socket(int fd, int type,
                                            struct gtp_dev *gtp)
{
        struct udp_tunnel_sock_cfg tuncfg = {NULL};
        struct socket *sock;
        struct sock *sk;
        int err;

        pr_debug("enable gtp on %d, %d\n", fd, type);

        sock = sockfd_lookup(fd, &err);
        if (!sock) {
                pr_debug("gtp socket fd=%d not found\n", fd);
                return NULL;
        }

        sk = sock->sk;
        if (sk->sk_protocol != IPPROTO_UDP ||
            sk->sk_type != SOCK_DGRAM ||
            (sk->sk_family != AF_INET && sk->sk_family != AF_INET6)) {
                pr_debug("socket fd=%d not UDP\n", fd);
                sk = ERR_PTR(-EINVAL);
                goto out_sock;
        }

        lock_sock(sk);
        if (sk->sk_user_data) {
                sk = ERR_PTR(-EBUSY);
                goto out_rel_sock;
        }

        sock_hold(sk);

        tuncfg.sk_user_data = gtp;
        tuncfg.encap_type = type;
        tuncfg.encap_rcv = gtp_encap_recv;
        tuncfg.encap_destroy = gtp_encap_destroy;

        setup_udp_tunnel_sock(sock_net(sock->sk), sock, &tuncfg);

out_rel_sock:
        release_sock(sock->sk);
out_sock:
        sockfd_put(sock);
        return sk;
}

static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[])
{
        struct sock *sk1u = NULL;
        struct sock *sk0 = NULL;

        if (!data[IFLA_GTP_FD0] && !data[IFLA_GTP_FD1])
                return -EINVAL;

        if (data[IFLA_GTP_FD0]) {
                u32 fd0 = nla_get_u32(data[IFLA_GTP_FD0]);

                sk0 = gtp_encap_enable_socket(fd0, UDP_ENCAP_GTP0, gtp);
                if (IS_ERR(sk0))
                        return PTR_ERR(sk0);
        }

        if (data[IFLA_GTP_FD1]) {
                u32 fd1 = nla_get_u32(data[IFLA_GTP_FD1]);

                sk1u = gtp_encap_enable_socket(fd1, UDP_ENCAP_GTP1U, gtp);
                if (IS_ERR(sk1u)) {
                        gtp_encap_disable_sock(sk0);
                        return PTR_ERR(sk1u);
                }
        }

        gtp->sk0 = sk0;
        gtp->sk1u = sk1u;

        return 0;
}

static struct gtp_dev *gtp_find_dev(struct net *src_net, struct nlattr *nla[])
{
        struct gtp_dev *gtp = NULL;
        struct net_device *dev;
        struct net *net;

        /* Examine the link attributes and figure out which network namespace
         * we are talking about.
         */
        if (nla[GTPA_NET_NS_FD])
                net = get_net_ns_by_fd(nla_get_u32(nla[GTPA_NET_NS_FD]));
        else
                net = get_net(src_net);

        if (IS_ERR(net))
                return NULL;

        /* Check if there's an existing gtpX device to configure */
        dev = dev_get_by_index_rcu(net, nla_get_u32(nla[GTPA_LINK]));
        if (dev && dev->netdev_ops == &gtp_netdev_ops)
                gtp = netdev_priv(dev);

        put_net(net);
        return gtp;
}

static void ipv4_pdp_fill(struct pdp_ctx *pctx, struct genl_info *info)
{
        pctx->gtp_version = nla_get_u32(info->attrs[GTPA_VERSION]);
        pctx->af = AF_INET;
        pctx->peer_addr_ip4.s_addr =
                nla_get_be32(info->attrs[GTPA_PEER_ADDRESS]);
        pctx->ms_addr_ip4.s_addr =
                nla_get_be32(info->attrs[GTPA_MS_ADDRESS]);

        switch (pctx->gtp_version) {
        case GTP_V0:
                /* According to TS 09.60, sections 7.5.1 and 7.5.2, the flow
                 * label needs to be the same for uplink and downlink packets,
                 * so let's annotate this.
                 */
                pctx->u.v0.tid = nla_get_u64(info->attrs[GTPA_TID]);
                pctx->u.v0.flow = nla_get_u16(info->attrs[GTPA_FLOW]);
                break;
        case GTP_V1:
                pctx->u.v1.i_tei = nla_get_u32(info->attrs[GTPA_I_TEI]);
                pctx->u.v1.o_tei = nla_get_u32(info->attrs[GTPA_O_TEI]);
                break;
        default:
                break;
        }
}

static struct pdp_ctx *gtp_pdp_add(struct gtp_dev *gtp, struct sock *sk,
                                   struct genl_info *info)
{
        struct pdp_ctx *pctx, *pctx_tid = NULL;
        struct net_device *dev = gtp->dev;
        u32 hash_ms, hash_tid = 0;
        unsigned int version;
        bool found = false;
        __be32 ms_addr;

        ms_addr = nla_get_be32(info->attrs[GTPA_MS_ADDRESS]);
        hash_ms = ipv4_hashfn(ms_addr) % gtp->hash_size;
        version = nla_get_u32(info->attrs[GTPA_VERSION]);

        pctx = ipv4_pdp_find(gtp, ms_addr);
        if (pctx)
                found = true;
        if (version == GTP_V0)
                pctx_tid = gtp0_pdp_find(gtp,
                                         nla_get_u64(info->attrs[GTPA_TID]));
        else if (version == GTP_V1)
                pctx_tid = gtp1_pdp_find(gtp,
                                         nla_get_u32(info->attrs[GTPA_I_TEI]));
        if (pctx_tid)
                found = true;

        if (found) {
                if (info->nlhdr->nlmsg_flags & NLM_F_EXCL)
                        return ERR_PTR(-EEXIST);
                if (info->nlhdr->nlmsg_flags & NLM_F_REPLACE)
                        return ERR_PTR(-EOPNOTSUPP);

                if (pctx && pctx_tid)
                        return ERR_PTR(-EEXIST);
                if (!pctx)
                        pctx = pctx_tid;

                ipv4_pdp_fill(pctx, info);

                if (pctx->gtp_version == GTP_V0)
                        netdev_dbg(dev, "GTPv0-U: update tunnel id = %llx (pdp %p)\n",
                                   pctx->u.v0.tid, pctx);
                else if (pctx->gtp_version == GTP_V1)
                        netdev_dbg(dev, "GTPv1-U: update tunnel id = %x/%x (pdp %p)\n",
                                   pctx->u.v1.i_tei, pctx->u.v1.o_tei, pctx);

                return pctx;

        }

        pctx = kmalloc(sizeof(*pctx), GFP_ATOMIC);
        if (pctx == NULL)
                return ERR_PTR(-ENOMEM);

        sock_hold(sk);
        pctx->sk = sk;
        pctx->dev = gtp->dev;
        ipv4_pdp_fill(pctx, info);
        atomic_set(&pctx->tx_seq, 0);

        switch (pctx->gtp_version) {
        case GTP_V0:
                /* TS 09.60: "The flow label identifies unambiguously a GTP
                 * flow.". We use the tid for this instead, I cannot find a
                 * situation in which this doesn't unambiguosly identify the
                 * PDP context.
                 */
                hash_tid = gtp0_hashfn(pctx->u.v0.tid) % gtp->hash_size;
                break;
        case GTP_V1:
                hash_tid = gtp1u_hashfn(pctx->u.v1.i_tei) % gtp->hash_size;
                break;
        }

        hlist_add_head_rcu(&pctx->hlist_addr, &gtp->addr_hash[hash_ms]);
        hlist_add_head_rcu(&pctx->hlist_tid, &gtp->tid_hash[hash_tid]);

        switch (pctx->gtp_version) {
        case GTP_V0:
                netdev_dbg(dev, "GTPv0-U: new PDP ctx id=%llx ssgn=%pI4 ms=%pI4 (pdp=%p)\n",
                           pctx->u.v0.tid, &pctx->peer_addr_ip4,
                           &pctx->ms_addr_ip4, pctx);
                break;
        case GTP_V1:
                netdev_dbg(dev, "GTPv1-U: new PDP ctx id=%x/%x ssgn=%pI4 ms=%pI4 (pdp=%p)\n",
                           pctx->u.v1.i_tei, pctx->u.v1.o_tei,
                           &pctx->peer_addr_ip4, &pctx->ms_addr_ip4, pctx);
                break;
        }

        return pctx;
}

static void pdp_context_free(struct rcu_head *head)
{
        struct pdp_ctx *pctx = container_of(head, struct pdp_ctx, rcu_head);

        sock_put(pctx->sk);
        kfree(pctx);
}

static void pdp_context_delete(struct pdp_ctx *pctx)
{
        hlist_del_rcu(&pctx->hlist_tid);
        hlist_del_rcu(&pctx->hlist_addr);
        call_rcu(&pctx->rcu_head, pdp_context_free);
}

static int gtp_tunnel_notify(struct pdp_ctx *pctx, u8 cmd, gfp_t allocation);

static int gtp_genl_new_pdp(struct sk_buff *skb, struct genl_info *info)
{
        unsigned int version;
        struct pdp_ctx *pctx;
        struct gtp_dev *gtp;
        struct sock *sk;
        int err;

        if (!info->attrs[GTPA_VERSION] ||
            !info->attrs[GTPA_LINK] ||
            !info->attrs[GTPA_PEER_ADDRESS] ||
            !info->attrs[GTPA_MS_ADDRESS])
                return -EINVAL;

        version = nla_get_u32(info->attrs[GTPA_VERSION]);

        switch (version) {
        case GTP_V0:
                if (!info->attrs[GTPA_TID] ||
                    !info->attrs[GTPA_FLOW])
                        return -EINVAL;
                break;
        case GTP_V1:
                if (!info->attrs[GTPA_I_TEI] ||
                    !info->attrs[GTPA_O_TEI])
                        return -EINVAL;
                break;

        default:
                return -EINVAL;
        }

        rtnl_lock();

        gtp = gtp_find_dev(sock_net(skb->sk), info->attrs);
        if (!gtp) {
                err = -ENODEV;
                goto out_unlock;
        }

        if (version == GTP_V0)
                sk = gtp->sk0;
        else if (version == GTP_V1)
                sk = gtp->sk1u;
        else
                sk = NULL;

        if (!sk) {
                err = -ENODEV;
                goto out_unlock;
        }

        pctx = gtp_pdp_add(gtp, sk, info);
        if (IS_ERR(pctx)) {
                err = PTR_ERR(pctx);
        } else {
                gtp_tunnel_notify(pctx, GTP_CMD_NEWPDP, GFP_KERNEL);
                err = 0;
        }

out_unlock:
        rtnl_unlock();
        return err;
}

static struct pdp_ctx *gtp_find_pdp_by_link(struct net *net,
                                            struct nlattr *nla[])
{
        struct gtp_dev *gtp;

        gtp = gtp_find_dev(net, nla);
        if (!gtp)
                return ERR_PTR(-ENODEV);

        if (nla[GTPA_MS_ADDRESS]) {
                __be32 ip = nla_get_be32(nla[GTPA_MS_ADDRESS]);

                return ipv4_pdp_find(gtp, ip);
        } else if (nla[GTPA_VERSION]) {
                u32 gtp_version = nla_get_u32(nla[GTPA_VERSION]);

                if (gtp_version == GTP_V0 && nla[GTPA_TID])
                        return gtp0_pdp_find(gtp, nla_get_u64(nla[GTPA_TID]));
                else if (gtp_version == GTP_V1 && nla[GTPA_I_TEI])
                        return gtp1_pdp_find(gtp, nla_get_u32(nla[GTPA_I_TEI]));
        }

        return ERR_PTR(-EINVAL);
}

static struct pdp_ctx *gtp_find_pdp(struct net *net, struct nlattr *nla[])
{
        struct pdp_ctx *pctx;

        if (nla[GTPA_LINK])
                pctx = gtp_find_pdp_by_link(net, nla);
        else
                pctx = ERR_PTR(-EINVAL);

        if (!pctx)
                pctx = ERR_PTR(-ENOENT);

        return pctx;
}

static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
{
        struct pdp_ctx *pctx;
        int err = 0;

        if (!info->attrs[GTPA_VERSION])
                return -EINVAL;

        rcu_read_lock();

        pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs);
        if (IS_ERR(pctx)) {
                err = PTR_ERR(pctx);
                goto out_unlock;
        }

        if (pctx->gtp_version == GTP_V0)
                netdev_dbg(pctx->dev, "GTPv0-U: deleting tunnel id = %llx (pdp %p)\n",
                           pctx->u.v0.tid, pctx);
        else if (pctx->gtp_version == GTP_V1)
                netdev_dbg(pctx->dev, "GTPv1-U: deleting tunnel id = %x/%x (pdp %p)\n",
                           pctx->u.v1.i_tei, pctx->u.v1.o_tei, pctx);

        gtp_tunnel_notify(pctx, GTP_CMD_DELPDP, GFP_ATOMIC);
        pdp_context_delete(pctx);

out_unlock:
        rcu_read_unlock();
        return err;
}

static int gtp_genl_fill_info(struct sk_buff *skb, u32 snd_portid, u32 snd_seq,
                              int flags, u32 type, struct pdp_ctx *pctx)
{
        void *genlh;

        genlh = genlmsg_put(skb, snd_portid, snd_seq, &gtp_genl_family, flags,
                            type);
        if (genlh == NULL)
                goto nlmsg_failure;

        if (nla_put_u32(skb, GTPA_VERSION, pctx->gtp_version) ||
            nla_put_u32(skb, GTPA_LINK, pctx->dev->ifindex) ||
            nla_put_be32(skb, GTPA_PEER_ADDRESS, pctx->peer_addr_ip4.s_addr) ||
            nla_put_be32(skb, GTPA_MS_ADDRESS, pctx->ms_addr_ip4.s_addr))
                goto nla_put_failure;

        switch (pctx->gtp_version) {
        case GTP_V0:
                if (nla_put_u64_64bit(skb, GTPA_TID, pctx->u.v0.tid, GTPA_PAD) ||
                    nla_put_u16(skb, GTPA_FLOW, pctx->u.v0.flow))
                        goto nla_put_failure;
                break;
        case GTP_V1:
                if (nla_put_u32(skb, GTPA_I_TEI, pctx->u.v1.i_tei) ||
                    nla_put_u32(skb, GTPA_O_TEI, pctx->u.v1.o_tei))
                        goto nla_put_failure;
                break;
        }
        genlmsg_end(skb, genlh);
        return 0;

nlmsg_failure:
nla_put_failure:
        genlmsg_cancel(skb, genlh);
        return -EMSGSIZE;
}

static int gtp_tunnel_notify(struct pdp_ctx *pctx, u8 cmd, gfp_t allocation)
{
        struct sk_buff *msg;
        int ret;

        msg = nlmsg_new(NLMSG_DEFAULT_SIZE, allocation);
        if (!msg)
                return -ENOMEM;

        ret = gtp_genl_fill_info(msg, 0, 0, 0, cmd, pctx);
        if (ret < 0) {
                nlmsg_free(msg);
                return ret;
        }

        ret = genlmsg_multicast_netns(&gtp_genl_family, dev_net(pctx->dev), msg,
                                      0, GTP_GENL_MCGRP, GFP_ATOMIC);
        return ret;
}

static int gtp_genl_get_pdp(struct sk_buff *skb, struct genl_info *info)
{
        struct pdp_ctx *pctx = NULL;
        struct sk_buff *skb2;
        int err;

        if (!info->attrs[GTPA_VERSION])
                return -EINVAL;

        rcu_read_lock();

        pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs);
        if (IS_ERR(pctx)) {
                err = PTR_ERR(pctx);
                goto err_unlock;
        }

        skb2 = genlmsg_new(NLMSG_GOODSIZE, GFP_ATOMIC);
        if (skb2 == NULL) {
                err = -ENOMEM;
                goto err_unlock;
        }

        err = gtp_genl_fill_info(skb2, NETLINK_CB(skb).portid, info->snd_seq,
                                 0, info->nlhdr->nlmsg_type, pctx);
        if (err < 0)
                goto err_unlock_free;

        rcu_read_unlock();
        return genlmsg_unicast(genl_info_net(info), skb2, info->snd_portid);

err_unlock_free:
        kfree_skb(skb2);
err_unlock:
        rcu_read_unlock();
        return err;
}

static int gtp_genl_dump_pdp(struct sk_buff *skb,
                                struct netlink_callback *cb)
{
        struct gtp_dev *last_gtp = (struct gtp_dev *)cb->args[2], *gtp;
        int i, j, bucket = cb->args[0], skip = cb->args[1];
        struct net *net = sock_net(skb->sk);
        struct pdp_ctx *pctx;
        struct gtp_net *gn;

        gn = net_generic(net, gtp_net_id);

        if (cb->args[4])
                return 0;

        rcu_read_lock();
        list_for_each_entry_rcu(gtp, &gn->gtp_dev_list, list) {
                if (last_gtp && last_gtp != gtp)
                        continue;
                else
                        last_gtp = NULL;

                for (i = bucket; i < gtp->hash_size; i++) {
                        j = 0;
                        hlist_for_each_entry_rcu(pctx, &gtp->tid_hash[i],
                                                 hlist_tid) {
                                if (j >= skip &&
                                    gtp_genl_fill_info(skb,
                                            NETLINK_CB(cb->skb).portid,
                                            cb->nlh->nlmsg_seq,
                                            NLM_F_MULTI,
                                            cb->nlh->nlmsg_type, pctx)) {
                                        cb->args[0] = i;
                                        cb->args[1] = j;
                                        cb->args[2] = (unsigned long)gtp;
                                        goto out;
                                }
                                j++;
                        }
                        skip = 0;
                }
                bucket = 0;
        }
        cb->args[4] = 1;
out:
        rcu_read_unlock();
        return skb->len;
}

static int gtp_genl_send_echo_req(struct sk_buff *skb, struct genl_info *info)
{
        struct sk_buff *skb_to_send;
        __be32 src_ip, dst_ip;
        unsigned int version;
        struct gtp_dev *gtp;
        struct flowi4 fl4;
        struct rtable *rt;
        struct sock *sk;
        __be16 port;
        int len;

        if (!info->attrs[GTPA_VERSION] ||
            !info->attrs[GTPA_LINK] ||
            !info->attrs[GTPA_PEER_ADDRESS] ||
            !info->attrs[GTPA_MS_ADDRESS])
                return -EINVAL;

        version = nla_get_u32(info->attrs[GTPA_VERSION]);
        dst_ip = nla_get_be32(info->attrs[GTPA_PEER_ADDRESS]);
        src_ip = nla_get_be32(info->attrs[GTPA_MS_ADDRESS]);

        gtp = gtp_find_dev(sock_net(skb->sk), info->attrs);
        if (!gtp)
                return -ENODEV;

        if (!gtp->sk_created)
                return -EOPNOTSUPP;
        if (!(gtp->dev->flags & IFF_UP))
                return -ENETDOWN;

        if (version == GTP_V0) {
                struct gtp0_header *gtp0_h;

                len = LL_RESERVED_SPACE(gtp->dev) + sizeof(struct gtp0_header) +
                        sizeof(struct iphdr) + sizeof(struct udphdr);

                skb_to_send = netdev_alloc_skb_ip_align(gtp->dev, len);
                if (!skb_to_send)
                        return -ENOMEM;

                sk = gtp->sk0;
                port = htons(GTP0_PORT);

                gtp0_h = skb_push(skb_to_send, sizeof(struct gtp0_header));
                memset(gtp0_h, 0, sizeof(struct gtp0_header));
                gtp0_build_echo_msg(gtp0_h, GTP_ECHO_REQ);
        } else if (version == GTP_V1) {
                struct gtp1_header_long *gtp1u_h;

                len = LL_RESERVED_SPACE(gtp->dev) +
                        sizeof(struct gtp1_header_long) +
                        sizeof(struct iphdr) + sizeof(struct udphdr);

                skb_to_send = netdev_alloc_skb_ip_align(gtp->dev, len);
                if (!skb_to_send)
                        return -ENOMEM;

                sk = gtp->sk1u;
                port = htons(GTP1U_PORT);

                gtp1u_h = skb_push(skb_to_send,
                                   sizeof(struct gtp1_header_long));
                memset(gtp1u_h, 0, sizeof(struct gtp1_header_long));
                gtp1u_build_echo_msg(gtp1u_h, GTP_ECHO_REQ);
        } else {
                return -ENODEV;
        }

        rt = ip4_route_output_gtp(&fl4, sk, dst_ip, src_ip);
        if (IS_ERR(rt)) {
                netdev_dbg(gtp->dev, "no route for echo request to %pI4\n",
                           &dst_ip);
                kfree_skb(skb_to_send);
                return -ENODEV;
        }

        udp_tunnel_xmit_skb(rt, sk, skb_to_send,
                            fl4.saddr, fl4.daddr,
                            fl4.flowi4_tos,
                            ip4_dst_hoplimit(&rt->dst),
                            0,
                            port, port,
                            !net_eq(sock_net(sk),
                                    dev_net(gtp->dev)),
                            false);
        return 0;
}

static const struct nla_policy gtp_genl_policy[GTPA_MAX + 1] = {
        [GTPA_LINK]             = { .type = NLA_U32, },
        [GTPA_VERSION]          = { .type = NLA_U32, },
        [GTPA_TID]              = { .type = NLA_U64, },
        [GTPA_PEER_ADDRESS]     = { .type = NLA_U32, },
        [GTPA_MS_ADDRESS]       = { .type = NLA_U32, },
        [GTPA_FLOW]             = { .type = NLA_U16, },
        [GTPA_NET_NS_FD]        = { .type = NLA_U32, },
        [GTPA_I_TEI]            = { .type = NLA_U32, },
        [GTPA_O_TEI]            = { .type = NLA_U32, },
};

static const struct genl_small_ops gtp_genl_ops[] = {
        {
                .cmd = GTP_CMD_NEWPDP,
                .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
                .doit = gtp_genl_new_pdp,
                .flags = GENL_ADMIN_PERM,
        },
        {
                .cmd = GTP_CMD_DELPDP,
                .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
                .doit = gtp_genl_del_pdp,
                .flags = GENL_ADMIN_PERM,
        },
        {
                .cmd = GTP_CMD_GETPDP,
                .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
                .doit = gtp_genl_get_pdp,
                .dumpit = gtp_genl_dump_pdp,
                .flags = GENL_ADMIN_PERM,
        },
        {
                .cmd = GTP_CMD_ECHOREQ,
                .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
                .doit = gtp_genl_send_echo_req,
                .flags = GENL_ADMIN_PERM,
        },
};

static struct genl_family gtp_genl_family __ro_after_init = {
        .name           = "gtp",
        .version        = 0,
        .hdrsize        = 0,
        .maxattr        = GTPA_MAX,
        .policy = gtp_genl_policy,
        .netnsok        = true,
        .module         = THIS_MODULE,
        .small_ops      = gtp_genl_ops,
        .n_small_ops    = ARRAY_SIZE(gtp_genl_ops),
        .mcgrps         = gtp_genl_mcgrps,
        .n_mcgrps       = ARRAY_SIZE(gtp_genl_mcgrps),
};

static int __net_init gtp_net_init(struct net *net)
{
        struct gtp_net *gn = net_generic(net, gtp_net_id);

        INIT_LIST_HEAD(&gn->gtp_dev_list);
        return 0;
}

static void __net_exit gtp_net_exit(struct net *net)
{
        struct gtp_net *gn = net_generic(net, gtp_net_id);
        struct gtp_dev *gtp;
        LIST_HEAD(list);

        rtnl_lock();
        list_for_each_entry(gtp, &gn->gtp_dev_list, list)
                gtp_dellink(gtp->dev, &list);

        unregister_netdevice_many(&list);
        rtnl_unlock();
}

static struct pernet_operations gtp_net_ops = {
        .init   = gtp_net_init,
        .exit   = gtp_net_exit,
        .id     = &gtp_net_id,
        .size   = sizeof(struct gtp_net),
};

static int __init gtp_init(void)
{
        int err;

        get_random_bytes(&gtp_h_initval, sizeof(gtp_h_initval));

        err = rtnl_link_register(&gtp_link_ops);
        if (err < 0)
                goto error_out;

        err = genl_register_family(&gtp_genl_family);
        if (err < 0)
                goto unreg_rtnl_link;

        err = register_pernet_subsys(&gtp_net_ops);
        if (err < 0)
                goto unreg_genl_family;

        pr_info("GTP module loaded (pdp ctx size %zd bytes)\n",
                sizeof(struct pdp_ctx));
        return 0;

unreg_genl_family:
        genl_unregister_family(&gtp_genl_family);
unreg_rtnl_link:
        rtnl_link_unregister(&gtp_link_ops);
error_out:
        pr_err("error loading GTP module loaded\n");
        return err;
}
late_initcall(gtp_init);

static void __exit gtp_fini(void)
{
        genl_unregister_family(&gtp_genl_family);
        rtnl_link_unregister(&gtp_link_ops);
        unregister_pernet_subsys(&gtp_net_ops);

        pr_info("GTP module unloaded\n");
}
module_exit(gtp_fini);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <hwelte@sysmocom.de>");
MODULE_DESCRIPTION("Interface driver for GTP encapsulated traffic");
MODULE_ALIAS_RTNL_LINK("gtp");
MODULE_ALIAS_GENL_FAMILY("gtp");