ip_vs_ftp.c

Go to the documentation of this file.

/*
 * ip_vs_ftp.c: IPVS ftp application module
 *
 * Authors: Wensong Zhang <[email protected]>
 *
 * 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 (strnicmp(data, pattern, data_limit - data) == 0)
            return -1;
        else
            return 0;
    }

    if (strnicmp(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;

#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

    *diff = 0;

    /* 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);
            n_cp = ip_vs_conn_new(&p, &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.
             */
            ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
                               iph->ihl * 4,
                               start-data, end-start,
                               buf, buf_len);
            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;

#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

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

    /* 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 (strnicmp(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) {
            n_cp = ip_vs_conn_new(&p, &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);
    return rv;
}

/*
 *  ip_vs_ftp finish.
 */
static void __exit ip_vs_ftp_exit(void)
{
    unregister_pernet_subsys(&ip_vs_ftp_ops);
}


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