// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * ip_vs_ftp.c: IPVS ftp application module
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *
 * Changes:
 *
 * 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 pr_fmt(fmt) "IPVS: " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/ctype.h>
#include <linux/inet.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 <linux/unaligned.h>

#include <net/ip_vs.h>


#define SERVER_STRING_PASV "227 "
#define CLIENT_STRING_PORT "PORT"
#define SERVER_STRING_EPSV "229 "
#define CLIENT_STRING_EPRT "EPRT"

enum {
        IP_VS_FTP_ACTIVE = 0,
        IP_VS_FTP_PORT = 0,
        IP_VS_FTP_PASV,
        IP_VS_FTP_EPRT,
        IP_VS_FTP_EPSV,
};

static bool exiting_module;
/*
 * 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");


static char *ip_vs_ftp_data_ptr(struct sk_buff *skb, struct ip_vs_iphdr *ipvsh)
{
        struct tcphdr *th = (struct tcphdr *)((char *)skb->data + ipvsh->len);

        if ((th->doff << 2) < sizeof(struct tcphdr))
                return NULL;

        return (char *)th + (th->doff << 2);
}

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". <addr,port> is in network order.
 * Parse extended format depending on ext. In this case addr can be pre-set.
 */
static int ip_vs_ftp_get_addrport(char *data, char *data_limit,
                                  const char *pattern, size_t plen,
                                  char skip, bool ext, int mode,
                                  union nf_inet_addr *addr, __be16 *port,
                                  __u16 af, char **start, char **end)
{
        char *s, c;
        unsigned char p[6];
        char edelim;
        __u16 hport;
        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) {
                bool found = false;

                for (;; s++) {
                        if (s == data_limit)
                                return -1;
                        if (!found) {
                                /* "(" is optional for non-extended format,
                                 * so catch the start of IPv4 address
                                 */
                                if (!ext && isdigit(*s))
                                        break;
                                if (*s == skip)
                                        found = true;
                        } else if (*s != skip) {
                                break;
                        }
                }
        }
        /* Old IPv4-only format? */
        if (!ext) {
                p[0] = 0;
                for (data = s; ; data++) {
                        if (data == data_limit)
                                return -1;
                        c = *data;
                        if (isdigit(c)) {
                                p[i] = p[i]*10 + c - '0';
                        } else if (c == ',' && i < 5) {
                                i++;
                                p[i] = 0;
                        } else {
                                /* unexpected character or terminator */
                                break;
                        }
                }

                if (i != 5)
                        return -1;

                *start = s;
                *end = data;
                addr->ip = get_unaligned((__be32 *) p);
                *port = get_unaligned((__be16 *) (p + 4));
                return 1;
        }
        if (s == data_limit)
                return -1;
        *start = s;
        edelim = *s++;
        if (edelim < 33 || edelim > 126)
                return -1;
        if (s == data_limit)
                return -1;
        if (*s == edelim) {
                /* Address family is usually missing for EPSV response */
                if (mode != IP_VS_FTP_EPSV)
                        return -1;
                s++;
                if (s == data_limit)
                        return -1;
                /* Then address should be missing too */
                if (*s != edelim)
                        return -1;
                /* Caller can pre-set addr, if needed */
                s++;
        } else {
                const char *ep;

                /* We allow address only from same family */
                if (af == AF_INET6 && *s != '2')
                        return -1;
                if (af == AF_INET && *s != '1')
                        return -1;
                s++;
                if (s == data_limit)
                        return -1;
                if (*s != edelim)
                        return -1;
                s++;
                if (s == data_limit)
                        return -1;
                if (af == AF_INET6) {
                        if (in6_pton(s, data_limit - s, (u8 *)addr, edelim,
                                     &ep) <= 0)
                                return -1;
                } else {
                        if (in4_pton(s, data_limit - s, (u8 *)addr, edelim,
                                     &ep) <= 0)
                                return -1;
                }
                s = (char *) ep;
                if (s == data_limit)
                        return -1;
                if (*s != edelim)
                        return -1;
                s++;
        }
        for (hport = 0; ; s++)
        {
                if (s == data_limit)
                        return -1;
                if (!isdigit(*s))
                        break;
                hport = hport * 10 + *s - '0';
        }
        if (s == data_limit || !hport || *s != edelim)
                return -1;
        s++;
        *end = s;
        *port = htons(hport);
        return 1;
}

/* Look at outgoing ftp packets to catch the response to a PASV/EPSV 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.
 * The extended format for EPSV response provides usually only port:
 *   "229 Entering Extended Passive Mode (|||ppp|)"
 */
static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
                         struct sk_buff *skb, int *diff,
                         struct ip_vs_iphdr *ipvsh)
{
        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;

        *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_ensure_writable(skb, skb->len))
                return 0;

        if (cp->app_data == (void *) IP_VS_FTP_PASV) {
                data = ip_vs_ftp_data_ptr(skb, ipvsh);
                data_limit = skb_tail_pointer(skb);

                if (!data || data >= data_limit)
                        return 1;

                if (ip_vs_ftp_get_addrport(data, data_limit,
                                           SERVER_STRING_PASV,
                                           sizeof(SERVER_STRING_PASV)-1,
                                           '(', false, IP_VS_FTP_PASV,
                                           &from, &port, cp->af,
                                           &start, &end) != 1)
                        return 1;

                IP_VS_DBG(7, "PASV response (%pI4:%u) -> %pI4:%u detected\n",
                          &from.ip, ntohs(port), &cp->caddr.ip, 0);
        } else if (cp->app_data == (void *) IP_VS_FTP_EPSV) {
                data = ip_vs_ftp_data_ptr(skb, ipvsh);
                data_limit = skb_tail_pointer(skb);

                if (!data || data >= data_limit)
                        return 1;

                /* Usually, data address is not specified but
                 * we support different address, so pre-set it.
                 */
                from = cp->daddr;
                if (ip_vs_ftp_get_addrport(data, data_limit,
                                           SERVER_STRING_EPSV,
                                           sizeof(SERVER_STRING_EPSV)-1,
                                           '(', true, IP_VS_FTP_EPSV,
                                           &from, &port, cp->af,
                                           &start, &end) != 1)
                        return 1;

                IP_VS_DBG_BUF(7, "EPSV response (%s:%u) -> %s:%u detected\n",
                              IP_VS_DBG_ADDR(cp->af, &from), ntohs(port),
                              IP_VS_DBG_ADDR(cp->af, &cp->caddr), 0);
        } else {
                return 1;
        }

        /* Now update or create a connection entry for it */
        {
                struct ip_vs_conn_param p;

                ip_vs_conn_fill_param(cp->ipvs, cp->af,
                                      ipvsh->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(cp->ipvs,
                                      cp->af, ipvsh->protocol, &cp->caddr,
                                      0, &cp->vaddr, port, &p);
                n_cp = ip_vs_conn_new(&p, cp->af, &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 */
        if (cp->app_data == (void *) IP_VS_FTP_PASV) {
                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);
        } else if (cp->app_data == (void *) IP_VS_FTP_EPSV) {
                from = n_cp->vaddr;
                port = n_cp->vport;
                /* Only port, client will use VIP for the data connection */
                snprintf(buf, sizeof(buf), "|||%u|",
                         ntohs(port));
        } else {
                *buf = 0;
        }
        buf_len = strlen(buf);

        ct = nf_ct_get(skb, &ctinfo);
        if (ct) {
                bool mangled;

                /* 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.
                 */
                mangled = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
                                                   ipvsh->len,
                                                   start - data,
                                                   end - start,
                                                   buf, buf_len);
                if (mangled) {
                        ip_vs_nfct_expect_related(skb, ct, n_cp,
                                                  ipvsh->protocol, 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.
         */

        cp->app_data = (void *) IP_VS_FTP_ACTIVE;
        ip_vs_tcp_conn_listen(n_cp);
        ip_vs_conn_put(n_cp);
        return ret;
}


/* Look at incoming ftp packets to catch the PASV/PORT/EPRT/EPSV 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.
 * Extended format:
 *      "EPSV\r\n" when client requests server address from same family
 *      "EPSV 1\r\n" when client requests IPv4 server address
 *      "EPSV 2\r\n" when client requests IPv6 server address
 *      "EPSV ALL\r\n" - not supported
 *      EPRT with specified delimiter (ASCII 33..126), "|" by default:
 *      "EPRT |1|IPv4ADDR|PORT|\r\n" when client provides IPv4 addrport
 *      "EPRT |2|IPv6ADDR|PORT|\r\n" when client provides IPv6 addrport
 */
static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
                        struct sk_buff *skb, int *diff,
                        struct ip_vs_iphdr *ipvsh)
{
        char *data, *data_start, *data_limit;
        char *start, *end;
        union nf_inet_addr to;
        __be16 port;
        struct ip_vs_conn *n_cp;

        /* 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_ensure_writable(skb, skb->len))
                return 0;

        data = data_start = ip_vs_ftp_data_ptr(skb, ipvsh);
        data_limit = skb_tail_pointer(skb);
        if (!data || data >= data_limit)
                return 1;

        while (data <= data_limit - 6) {
                if (cp->af == AF_INET &&
                    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 = (void *) IP_VS_FTP_PASV;
                        return 1;
                }

                /* EPSV or EPSV<space><net-prt> */
                if (strncasecmp(data, "EPSV", 4) == 0 &&
                    (data[4] == ' ' || data[4] == '\r')) {
                        if (data[4] == ' ') {
                                char proto = data[5];

                                if (data > data_limit - 7 || data[6] != '\r')
                                        return 1;

#ifdef CONFIG_IP_VS_IPV6
                                if (cp->af == AF_INET6 && proto == '2') {
                                } else
#endif
                                if (cp->af == AF_INET && proto == '1') {
                                } else {
                                        return 1;
                                }
                        }
                        /* Extended Passive mode on */
                        IP_VS_DBG(7, "got EPSV at %td of %td\n",
                                  data - data_start,
                                  data_limit - data_start);
                        cp->app_data = (void *) IP_VS_FTP_EPSV;
                        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 (cp->af == AF_INET &&
            ip_vs_ftp_get_addrport(data_start, data_limit,
                                   CLIENT_STRING_PORT,
                                   sizeof(CLIENT_STRING_PORT)-1,
                                   ' ', false, IP_VS_FTP_PORT,
                                   &to, &port, cp->af,
                                   &start, &end) == 1) {

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

                /* Now update or create a connection entry for it */
                IP_VS_DBG(7, "protocol %s %pI4:%u %pI4:%u\n",
                          ip_vs_proto_name(ipvsh->protocol),
                          &to.ip, ntohs(port), &cp->vaddr.ip,
                          ntohs(cp->vport)-1);
        } else if (ip_vs_ftp_get_addrport(data_start, data_limit,
                                          CLIENT_STRING_EPRT,
                                          sizeof(CLIENT_STRING_EPRT)-1,
                                          ' ', true, IP_VS_FTP_EPRT,
                                          &to, &port, cp->af,
                                          &start, &end) == 1) {

                IP_VS_DBG_BUF(7, "EPRT %s:%u detected\n",
                              IP_VS_DBG_ADDR(cp->af, &to), ntohs(port));

                /* Now update or create a connection entry for it */
                IP_VS_DBG_BUF(7, "protocol %s %s:%u %s:%u\n",
                              ip_vs_proto_name(ipvsh->protocol),
                              IP_VS_DBG_ADDR(cp->af, &to), ntohs(port),
                              IP_VS_DBG_ADDR(cp->af, &cp->vaddr),
                              ntohs(cp->vport)-1);
        } else {
                return 1;
        }

        /* Passive mode off */
        cp->app_data = (void *) IP_VS_FTP_ACTIVE;

        {
                struct ip_vs_conn_param p;
                ip_vs_conn_fill_param(cp->ipvs, cp->af,
                                      ipvsh->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->af, &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
         */
        ip_vs_tcp_conn_listen(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(ipvs, &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(ipvs, app, app->protocol, ports[i]);
                if (ret)
                        goto err_unreg;
        }
        return 0;

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

        if (!ipvs || !exiting_module)
                return;

        unregister_ip_vs_app(ipvs, &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)
{
        /* rcu_barrier() is called by netns on error */
        return register_pernet_subsys(&ip_vs_ftp_ops);
}

/*
 *      ip_vs_ftp finish.
 */
static void __exit ip_vs_ftp_exit(void)
{
        exiting_module = true;
        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");
MODULE_DESCRIPTION("ipvs ftp helper");