/*
 * ip_vs_ftp.c: IPVS ftp application module
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *
 * Changes:
 *
 *
 *      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.
 *
 * Most code here is taken from ip_masq_ftp.c in kernel 2.2. The difference
 * is that ip_vs_ftp module handles the reverse direction to ip_masq_ftp.
 *
 *              IP_MASQ_FTP ftp masquerading module
 *
 * Version:     @(#)ip_masq_ftp.c 0.04   02/05/96
 *
 * Author:      Wouter Gadeyne
 *
 */

#define KMSG_COMPONENT "IPVS"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/netfilter.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <linux/gfp.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <asm/unaligned.h>

#include <net/ip_vs.h>


#define SERVER_STRING "227 "
#define CLIENT_STRING "PORT"


/*
 * List of ports (up to IP_VS_APP_MAX_PORTS) to be handled by helper
 * First port is set to the default port.
 */
static unsigned int ports_count = 1;
static unsigned short ports[IP_VS_APP_MAX_PORTS] = {21, 0};
module_param_array(ports, ushort, &ports_count, 0444);
MODULE_PARM_DESC(ports, "Ports to monitor for FTP control commands");


/*      Dummy variable */
static int ip_vs_ftp_pasv;


static int
ip_vs_ftp_init_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
{
        /* We use connection tracking for the command connection */
        cp->flags |= IP_VS_CONN_F_NFCT;
        return 0;
}


static int
ip_vs_ftp_done_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
{
        return 0;
}


/*
 * Get <addr,port> from the string "xxx.xxx.xxx.xxx,ppp,ppp", started
 * with the "pattern", ignoring before "skip" and terminated with
 * the "term" character.
 * <addr,port> is in network order.
 */
static int ip_vs_ftp_get_addrport(char *data, char *data_limit,
                                  const char *pattern, size_t plen,
                                  char skip, char term,
                                  __be32 *addr, __be16 *port,
                                  char **start, char **end)
{
        char *s, c;
        unsigned char p[6];
        int i = 0;

        if (data_limit - data < plen) {
                /* check if there is partial match */
                if (strncasecmp(data, pattern, data_limit - data) == 0)
                        return -1;
                else
                        return 0;
        }

        if (strncasecmp(data, pattern, plen) != 0) {
                return 0;
        }
        s = data + plen;
        if (skip) {
                int found = 0;

                for (;; s++) {
                        if (s == data_limit)
                                return -1;
                        if (!found) {
                                if (*s == skip)
                                        found = 1;
                        } else if (*s != skip) {
                                break;
                        }
                }
        }

        for (data = s; ; data++) {
                if (data == data_limit)
                        return -1;
                if (*data == term)
                        break;
        }
        *end = data;

        memset(p, 0, sizeof(p));
        for (data = s; ; data++) {
                c = *data;
                if (c == term)
                        break;
                if (c >= '0' && c <= '9') {
                        p[i] = p[i]*10 + c - '0';
                } else if (c == ',' && i < 5) {
                        i++;
                } else {
                        /* unexpected character */
                        return -1;
                }
        }

        if (i != 5)
                return -1;

        *start = s;
        *addr = get_unaligned((__be32 *) p);
        *port = get_unaligned((__be16 *) (p + 4));
        return 1;
}

/*
 * Look at outgoing ftp packets to catch the response to a PASV command
 * from the server (inside-to-outside).
 * When we see one, we build a connection entry with the client address,
 * client port 0 (unknown at the moment), the server address and the
 * server port.  Mark the current connection entry as a control channel
 * of the new entry. All this work is just to make the data connection
 * can be scheduled to the right server later.
 *
 * The outgoing packet should be something like
 *   "227 Entering Passive Mode (xxx,xxx,xxx,xxx,ppp,ppp)".
 * xxx,xxx,xxx,xxx is the server address, ppp,ppp is the server port number.
 */
static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
                         struct sk_buff *skb, int *diff)
{
        struct iphdr *iph;
        struct tcphdr *th;
        char *data, *data_limit;
        char *start, *end;
        union nf_inet_addr from;
        __be16 port;
        struct ip_vs_conn *n_cp;
        char buf[24];           /* xxx.xxx.xxx.xxx,ppp,ppp\000 */
        unsigned int buf_len;
        int ret = 0;
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct;
        struct net *net;

        *diff = 0;

#ifdef CONFIG_IP_VS_IPV6
        /* This application helper doesn't work with IPv6 yet,
         * so turn this into a no-op for IPv6 packets
         */
        if (cp->af == AF_INET6)
                return 1;
#endif

        /* Only useful for established sessions */
        if (cp->state != IP_VS_TCP_S_ESTABLISHED)
                return 1;

        /* Linear packets are much easier to deal with. */
        if (!skb_make_writable(skb, skb->len))
                return 0;

        if (cp->app_data == &ip_vs_ftp_pasv) {
                iph = ip_hdr(skb);
                th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);
                data = (char *)th + (th->doff << 2);
                data_limit = skb_tail_pointer(skb);

                if (ip_vs_ftp_get_addrport(data, data_limit,
                                           SERVER_STRING,
                                           sizeof(SERVER_STRING)-1,
                                           '(', ')',
                                           &from.ip, &port,
                                           &start, &end) != 1)
                        return 1;

                IP_VS_DBG(7, "PASV response (%pI4:%d) -> %pI4:%d detected\n",
                          &from.ip, ntohs(port), &cp->caddr.ip, 0);

                /*
                 * Now update or create an connection entry for it
                 */
                {
                        struct ip_vs_conn_param p;
                        ip_vs_conn_fill_param(ip_vs_conn_net(cp), AF_INET,
                                              iph->protocol, &from, port,
                                              &cp->caddr, 0, &p);
                        n_cp = ip_vs_conn_out_get(&p);
                }
                if (!n_cp) {
                        struct ip_vs_conn_param p;
                        ip_vs_conn_fill_param(ip_vs_conn_net(cp),
                                              AF_INET, IPPROTO_TCP, &cp->caddr,
                                              0, &cp->vaddr, port, &p);
                        /* As above, this is ipv4 only */
                        n_cp = ip_vs_conn_new(&p, AF_INET, &from, port,
                                              IP_VS_CONN_F_NO_CPORT |
                                              IP_VS_CONN_F_NFCT,
                                              cp->dest, skb->mark);
                        if (!n_cp)
                                return 0;

                        /* add its controller */
                        ip_vs_control_add(n_cp, cp);
                }

                /*
                 * Replace the old passive address with the new one
                 */
                from.ip = n_cp->vaddr.ip;
                port = n_cp->vport;
                snprintf(buf, sizeof(buf), "%u,%u,%u,%u,%u,%u",
                         ((unsigned char *)&from.ip)[0],
                         ((unsigned char *)&from.ip)[1],
                         ((unsigned char *)&from.ip)[2],
                         ((unsigned char *)&from.ip)[3],
                         ntohs(port) >> 8,
                         ntohs(port) & 0xFF);

                buf_len = strlen(buf);

                ct = nf_ct_get(skb, &ctinfo);
                if (ct && !nf_ct_is_untracked(ct) && nfct_nat(ct)) {
                        /* If mangling fails this function will return 0
                         * which will cause the packet to be dropped.
                         * Mangling can only fail under memory pressure,
                         * hopefully it will succeed on the retransmitted
                         * packet.
                         */
                        rcu_read_lock();
                        ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
                                                       iph->ihl * 4,
                                                       start-data, end-start,
                                                       buf, buf_len);
                        rcu_read_unlock();
                        if (ret) {
                                ip_vs_nfct_expect_related(skb, ct, n_cp,
                                                          IPPROTO_TCP, 0, 0);
                                if (skb->ip_summed == CHECKSUM_COMPLETE)
                                        skb->ip_summed = CHECKSUM_UNNECESSARY;
                                /* csum is updated */
                                ret = 1;
                        }
                }

                /*
                 * Not setting 'diff' is intentional, otherwise the sequence
                 * would be adjusted twice.
                 */

                net = skb_net(skb);
                cp->app_data = NULL;
                ip_vs_tcp_conn_listen(net, n_cp);
                ip_vs_conn_put(n_cp);
                return ret;
        }
        return 1;
}


/*
 * Look at incoming ftp packets to catch the PASV/PORT command
 * (outside-to-inside).
 *
 * The incoming packet having the PORT command should be something like
 *      "PORT xxx,xxx,xxx,xxx,ppp,ppp\n".
 * xxx,xxx,xxx,xxx is the client address, ppp,ppp is the client port number.
 * In this case, we create a connection entry using the client address and
 * port, so that the active ftp data connection from the server can reach
 * the client.
 */
static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
                        struct sk_buff *skb, int *diff)
{
        struct iphdr *iph;
        struct tcphdr *th;
        char *data, *data_start, *data_limit;
        char *start, *end;
        union nf_inet_addr to;
        __be16 port;
        struct ip_vs_conn *n_cp;
        struct net *net;

        /* no diff required for incoming packets */
        *diff = 0;

#ifdef CONFIG_IP_VS_IPV6
        /* This application helper doesn't work with IPv6 yet,
         * so turn this into a no-op for IPv6 packets
         */
        if (cp->af == AF_INET6)
                return 1;
#endif

        /* Only useful for established sessions */
        if (cp->state != IP_VS_TCP_S_ESTABLISHED)
                return 1;

        /* Linear packets are much easier to deal with. */
        if (!skb_make_writable(skb, skb->len))
                return 0;

        /*
         * Detecting whether it is passive
         */
        iph = ip_hdr(skb);
        th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);

        /* Since there may be OPTIONS in the TCP packet and the HLEN is
           the length of the header in 32-bit multiples, it is accurate
           to calculate data address by th+HLEN*4 */
        data = data_start = (char *)th + (th->doff << 2);
        data_limit = skb_tail_pointer(skb);

        while (data <= data_limit - 6) {
                if (strncasecmp(data, "PASV\r\n", 6) == 0) {
                        /* Passive mode on */
                        IP_VS_DBG(7, "got PASV at %td of %td\n",
                                  data - data_start,
                                  data_limit - data_start);
                        cp->app_data = &ip_vs_ftp_pasv;
                        return 1;
                }
                data++;
        }

        /*
         * To support virtual FTP server, the scenerio is as follows:
         *       FTP client ----> Load Balancer ----> FTP server
         * First detect the port number in the application data,
         * then create a new connection entry for the coming data
         * connection.
         */
        if (ip_vs_ftp_get_addrport(data_start, data_limit,
                                   CLIENT_STRING, sizeof(CLIENT_STRING)-1,
                                   ' ', '\r', &to.ip, &port,
                                   &start, &end) != 1)
                return 1;

        IP_VS_DBG(7, "PORT %pI4:%d detected\n", &to.ip, ntohs(port));

        /* Passive mode off */
        cp->app_data = NULL;

        /*
         * Now update or create a connection entry for it
         */
        IP_VS_DBG(7, "protocol %s %pI4:%d %pI4:%d\n",
                  ip_vs_proto_name(iph->protocol),
                  &to.ip, ntohs(port), &cp->vaddr.ip, 0);

        {
                struct ip_vs_conn_param p;
                ip_vs_conn_fill_param(ip_vs_conn_net(cp), AF_INET,
                                      iph->protocol, &to, port, &cp->vaddr,
                                      htons(ntohs(cp->vport)-1), &p);
                n_cp = ip_vs_conn_in_get(&p);
                if (!n_cp) {
                        /* This is ipv4 only */
                        n_cp = ip_vs_conn_new(&p, AF_INET, &cp->daddr,
                                              htons(ntohs(cp->dport)-1),
                                              IP_VS_CONN_F_NFCT, cp->dest,
                                              skb->mark);
                        if (!n_cp)
                                return 0;

                        /* add its controller */
                        ip_vs_control_add(n_cp, cp);
                }
        }

        /*
         *      Move tunnel to listen state
         */
        net = skb_net(skb);
        ip_vs_tcp_conn_listen(net, n_cp);
        ip_vs_conn_put(n_cp);

        return 1;
}


static struct ip_vs_app ip_vs_ftp = {
        .name =         "ftp",
        .type =         IP_VS_APP_TYPE_FTP,
        .protocol =     IPPROTO_TCP,
        .module =       THIS_MODULE,
        .incs_list =    LIST_HEAD_INIT(ip_vs_ftp.incs_list),
        .init_conn =    ip_vs_ftp_init_conn,
        .done_conn =    ip_vs_ftp_done_conn,
        .bind_conn =    NULL,
        .unbind_conn =  NULL,
        .pkt_out =      ip_vs_ftp_out,
        .pkt_in =       ip_vs_ftp_in,
};

/*
 *      per netns ip_vs_ftp initialization
 */
static int __net_init __ip_vs_ftp_init(struct net *net)
{
        int i, ret;
        struct ip_vs_app *app;
        struct netns_ipvs *ipvs = net_ipvs(net);

        if (!ipvs)
                return -ENOENT;

        app = register_ip_vs_app(net, &ip_vs_ftp);
        if (IS_ERR(app))
                return PTR_ERR(app);

        for (i = 0; i < ports_count; i++) {
                if (!ports[i])
                        continue;
                ret = register_ip_vs_app_inc(net, app, app->protocol, ports[i]);
                if (ret)
                        goto err_unreg;
                pr_info("%s: loaded support on port[%d] = %d\n",
                        app->name, i, ports[i]);
        }
        return 0;

err_unreg:
        unregister_ip_vs_app(net, &ip_vs_ftp);
        return ret;
}
/*
 *      netns exit
 */
static void __ip_vs_ftp_exit(struct net *net)
{
        unregister_ip_vs_app(net, &ip_vs_ftp);
}

static struct pernet_operations ip_vs_ftp_ops = {
        .init = __ip_vs_ftp_init,
        .exit = __ip_vs_ftp_exit,
};

static int __init ip_vs_ftp_init(void)
{
        int rv;

        rv = register_pernet_subsys(&ip_vs_ftp_ops);
        /* rcu_barrier() is called by netns on error */
        return rv;
}

/*
 *      ip_vs_ftp finish.
 */
static void __exit ip_vs_ftp_exit(void)
{
        unregister_pernet_subsys(&ip_vs_ftp_ops);
        /* rcu_barrier() is called by netns */
}


module_init(ip_vs_ftp_init);
module_exit(ip_vs_ftp_exit);
MODULE_LICENSE("GPL");