/*
 * ip_vs_app.c: Application module support for IPVS
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *
 *              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_app.c in kernel 2.2. The difference
 * is that ip_vs_app module handles the reverse direction (incoming requests
 * and outgoing responses).
 *
 *              IP_MASQ_APP application masquerading module
 *
 * Author:      Juan Jose Ciarlante, <jjciarla@raiz.uncu.edu.ar>
 *
 */

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

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/netfilter.h>
#include <net/net_namespace.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <asm/system.h>
#include <linux/stat.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>

#include <net/ip_vs.h>

EXPORT_SYMBOL(register_ip_vs_app);
EXPORT_SYMBOL(unregister_ip_vs_app);
EXPORT_SYMBOL(register_ip_vs_app_inc);

/* ipvs application list head */
static LIST_HEAD(ip_vs_app_list);
static DEFINE_MUTEX(__ip_vs_app_mutex);


/*
 *      Get an ip_vs_app object
 */
static inline int ip_vs_app_get(struct ip_vs_app *app)
{
        return try_module_get(app->module);
}


static inline void ip_vs_app_put(struct ip_vs_app *app)
{
        module_put(app->module);
}


/*
 *      Allocate/initialize app incarnation and register it in proto apps.
 */
static int
ip_vs_app_inc_new(struct ip_vs_app *app, __u16 proto, __u16 port)
{
        struct ip_vs_protocol *pp;
        struct ip_vs_app *inc;
        int ret;

        if (!(pp = ip_vs_proto_get(proto)))
                return -EPROTONOSUPPORT;

        if (!pp->unregister_app)
                return -EOPNOTSUPP;

        inc = kmemdup(app, sizeof(*inc), GFP_KERNEL);
        if (!inc)
                return -ENOMEM;
        INIT_LIST_HEAD(&inc->p_list);
        INIT_LIST_HEAD(&inc->incs_list);
        inc->app = app;
        inc->port = htons(port);
        atomic_set(&inc->usecnt, 0);

        if (app->timeouts) {
                inc->timeout_table =
                        ip_vs_create_timeout_table(app->timeouts,
                                                   app->timeouts_size);
                if (!inc->timeout_table) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        ret = pp->register_app(inc);
        if (ret)
                goto out;

        list_add(&inc->a_list, &app->incs_list);
        IP_VS_DBG(9, "%s application %s:%u registered\n",
                  pp->name, inc->name, inc->port);

        return 0;

  out:
        kfree(inc->timeout_table);
        kfree(inc);
        return ret;
}


/*
 *      Release app incarnation
 */
static void
ip_vs_app_inc_release(struct ip_vs_app *inc)
{
        struct ip_vs_protocol *pp;

        if (!(pp = ip_vs_proto_get(inc->protocol)))
                return;

        if (pp->unregister_app)
                pp->unregister_app(inc);

        IP_VS_DBG(9, "%s App %s:%u unregistered\n",
                  pp->name, inc->name, inc->port);

        list_del(&inc->a_list);

        kfree(inc->timeout_table);
        kfree(inc);
}


/*
 *      Get reference to app inc (only called from softirq)
 *
 */
int ip_vs_app_inc_get(struct ip_vs_app *inc)
{
        int result;

        atomic_inc(&inc->usecnt);
        if (unlikely((result = ip_vs_app_get(inc->app)) != 1))
                atomic_dec(&inc->usecnt);
        return result;
}


/*
 *      Put the app inc (only called from timer or net softirq)
 */
void ip_vs_app_inc_put(struct ip_vs_app *inc)
{
        ip_vs_app_put(inc->app);
        atomic_dec(&inc->usecnt);
}


/*
 *      Register an application incarnation in protocol applications
 */
int
register_ip_vs_app_inc(struct ip_vs_app *app, __u16 proto, __u16 port)
{
        int result;

        mutex_lock(&__ip_vs_app_mutex);

        result = ip_vs_app_inc_new(app, proto, port);

        mutex_unlock(&__ip_vs_app_mutex);

        return result;
}


/*
 *      ip_vs_app registration routine
 */
int register_ip_vs_app(struct ip_vs_app *app)
{
        /* increase the module use count */
        ip_vs_use_count_inc();

        mutex_lock(&__ip_vs_app_mutex);

        list_add(&app->a_list, &ip_vs_app_list);

        mutex_unlock(&__ip_vs_app_mutex);

        return 0;
}


/*
 *      ip_vs_app unregistration routine
 *      We are sure there are no app incarnations attached to services
 */
void unregister_ip_vs_app(struct ip_vs_app *app)
{
        struct ip_vs_app *inc, *nxt;

        mutex_lock(&__ip_vs_app_mutex);

        list_for_each_entry_safe(inc, nxt, &app->incs_list, a_list) {
                ip_vs_app_inc_release(inc);
        }

        list_del(&app->a_list);

        mutex_unlock(&__ip_vs_app_mutex);

        /* decrease the module use count */
        ip_vs_use_count_dec();
}


/*
 *      Bind ip_vs_conn to its ip_vs_app (called by cp constructor)
 */
int ip_vs_bind_app(struct ip_vs_conn *cp, struct ip_vs_protocol *pp)
{
        return pp->app_conn_bind(cp);
}


/*
 *      Unbind cp from application incarnation (called by cp destructor)
 */
void ip_vs_unbind_app(struct ip_vs_conn *cp)
{
        struct ip_vs_app *inc = cp->app;

        if (!inc)
                return;

        if (inc->unbind_conn)
                inc->unbind_conn(inc, cp);
        if (inc->done_conn)
                inc->done_conn(inc, cp);
        ip_vs_app_inc_put(inc);
        cp->app = NULL;
}


/*
 *      Fixes th->seq based on ip_vs_seq info.
 */
static inline void vs_fix_seq(const struct ip_vs_seq *vseq, struct tcphdr *th)
{
        __u32 seq = ntohl(th->seq);

        /*
         *      Adjust seq with delta-offset for all packets after
         *      the most recent resized pkt seq and with previous_delta offset
         *      for all packets before most recent resized pkt seq.
         */
        if (vseq->delta || vseq->previous_delta) {
                if(after(seq, vseq->init_seq)) {
                        th->seq = htonl(seq + vseq->delta);
                        IP_VS_DBG(9, "%s(): added delta (%d) to seq\n",
                                  __func__, vseq->delta);
                } else {
                        th->seq = htonl(seq + vseq->previous_delta);
                        IP_VS_DBG(9, "%s(): added previous_delta (%d) to seq\n",
                                  __func__, vseq->previous_delta);
                }
        }
}


/*
 *      Fixes th->ack_seq based on ip_vs_seq info.
 */
static inline void
vs_fix_ack_seq(const struct ip_vs_seq *vseq, struct tcphdr *th)
{
        __u32 ack_seq = ntohl(th->ack_seq);

        /*
         * Adjust ack_seq with delta-offset for
         * the packets AFTER most recent resized pkt has caused a shift
         * for packets before most recent resized pkt, use previous_delta
         */
        if (vseq->delta || vseq->previous_delta) {
                /* since ack_seq is the number of octet that is expected
                   to receive next, so compare it with init_seq+delta */
                if(after(ack_seq, vseq->init_seq+vseq->delta)) {
                        th->ack_seq = htonl(ack_seq - vseq->delta);
                        IP_VS_DBG(9, "%s(): subtracted delta "
                                  "(%d) from ack_seq\n", __func__, vseq->delta);

                } else {
                        th->ack_seq = htonl(ack_seq - vseq->previous_delta);
                        IP_VS_DBG(9, "%s(): subtracted "
                                  "previous_delta (%d) from ack_seq\n",
                                  __func__, vseq->previous_delta);
                }
        }
}


/*
 *      Updates ip_vs_seq if pkt has been resized
 *      Assumes already checked proto==IPPROTO_TCP and diff!=0.
 */
static inline void vs_seq_update(struct ip_vs_conn *cp, struct ip_vs_seq *vseq,
                                 unsigned flag, __u32 seq, int diff)
{
        /* spinlock is to keep updating cp->flags atomic */
        spin_lock(&cp->lock);
        if (!(cp->flags & flag) || after(seq, vseq->init_seq)) {
                vseq->previous_delta = vseq->delta;
                vseq->delta += diff;
                vseq->init_seq = seq;
                cp->flags |= flag;
        }
        spin_unlock(&cp->lock);
}

static inline int app_tcp_pkt_out(struct ip_vs_conn *cp, struct sk_buff *skb,
                                  struct ip_vs_app *app)
{
        int diff;
        const unsigned int tcp_offset = ip_hdrlen(skb);
        struct tcphdr *th;
        __u32 seq;

        if (!skb_make_writable(skb, tcp_offset + sizeof(*th)))
                return 0;

        th = (struct tcphdr *)(skb_network_header(skb) + tcp_offset);

        /*
         *      Remember seq number in case this pkt gets resized
         */
        seq = ntohl(th->seq);

        /*
         *      Fix seq stuff if flagged as so.
         */
        if (cp->flags & IP_VS_CONN_F_OUT_SEQ)
                vs_fix_seq(&cp->out_seq, th);
        if (cp->flags & IP_VS_CONN_F_IN_SEQ)
                vs_fix_ack_seq(&cp->in_seq, th);

        /*
         *      Call private output hook function
         */
        if (app->pkt_out == NULL)
                return 1;

        if (!app->pkt_out(app, cp, skb, &diff))
                return 0;

        /*
         *      Update ip_vs seq stuff if len has changed.
         */
        if (diff != 0)
                vs_seq_update(cp, &cp->out_seq,
                              IP_VS_CONN_F_OUT_SEQ, seq, diff);

        return 1;
}

/*
 *      Output pkt hook. Will call bound ip_vs_app specific function
 *      called by ipvs packet handler, assumes previously checked cp!=NULL
 *      returns false if it can't handle packet (oom)
 */
int ip_vs_app_pkt_out(struct ip_vs_conn *cp, struct sk_buff *skb)
{
        struct ip_vs_app *app;

        /*
         *      check if application module is bound to
         *      this ip_vs_conn.
         */
        if ((app = cp->app) == NULL)
                return 1;

        /* TCP is complicated */
        if (cp->protocol == IPPROTO_TCP)
                return app_tcp_pkt_out(cp, skb, app);

        /*
         *      Call private output hook function
         */
        if (app->pkt_out == NULL)
                return 1;

        return app->pkt_out(app, cp, skb, NULL);
}


static inline int app_tcp_pkt_in(struct ip_vs_conn *cp, struct sk_buff *skb,
                                 struct ip_vs_app *app)
{
        int diff;
        const unsigned int tcp_offset = ip_hdrlen(skb);
        struct tcphdr *th;
        __u32 seq;

        if (!skb_make_writable(skb, tcp_offset + sizeof(*th)))
                return 0;

        th = (struct tcphdr *)(skb_network_header(skb) + tcp_offset);

        /*
         *      Remember seq number in case this pkt gets resized
         */
        seq = ntohl(th->seq);

        /*
         *      Fix seq stuff if flagged as so.
         */
        if (cp->flags & IP_VS_CONN_F_IN_SEQ)
                vs_fix_seq(&cp->in_seq, th);
        if (cp->flags & IP_VS_CONN_F_OUT_SEQ)
                vs_fix_ack_seq(&cp->out_seq, th);

        /*
         *      Call private input hook function
         */
        if (app->pkt_in == NULL)
                return 1;

        if (!app->pkt_in(app, cp, skb, &diff))
                return 0;

        /*
         *      Update ip_vs seq stuff if len has changed.
         */
        if (diff != 0)
                vs_seq_update(cp, &cp->in_seq,
                              IP_VS_CONN_F_IN_SEQ, seq, diff);

        return 1;
}

/*
 *      Input pkt hook. Will call bound ip_vs_app specific function
 *      called by ipvs packet handler, assumes previously checked cp!=NULL.
 *      returns false if can't handle packet (oom).
 */
int ip_vs_app_pkt_in(struct ip_vs_conn *cp, struct sk_buff *skb)
{
        struct ip_vs_app *app;

        /*
         *      check if application module is bound to
         *      this ip_vs_conn.
         */
        if ((app = cp->app) == NULL)
                return 1;

        /* TCP is complicated */
        if (cp->protocol == IPPROTO_TCP)
                return app_tcp_pkt_in(cp, skb, app);

        /*
         *      Call private input hook function
         */
        if (app->pkt_in == NULL)
                return 1;

        return app->pkt_in(app, cp, skb, NULL);
}


#ifdef CONFIG_PROC_FS
/*
 *      /proc/net/ip_vs_app entry function
 */

static struct ip_vs_app *ip_vs_app_idx(loff_t pos)
{
        struct ip_vs_app *app, *inc;

        list_for_each_entry(app, &ip_vs_app_list, a_list) {
                list_for_each_entry(inc, &app->incs_list, a_list) {
                        if (pos-- == 0)
                                return inc;
                }
        }
        return NULL;

}

static void *ip_vs_app_seq_start(struct seq_file *seq, loff_t *pos)
{
        mutex_lock(&__ip_vs_app_mutex);

        return *pos ? ip_vs_app_idx(*pos - 1) : SEQ_START_TOKEN;
}

static void *ip_vs_app_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct ip_vs_app *inc, *app;
        struct list_head *e;

        ++*pos;
        if (v == SEQ_START_TOKEN)
                return ip_vs_app_idx(0);

        inc = v;
        app = inc->app;

        if ((e = inc->a_list.next) != &app->incs_list)
                return list_entry(e, struct ip_vs_app, a_list);

        /* go on to next application */
        for (e = app->a_list.next; e != &ip_vs_app_list; e = e->next) {
                app = list_entry(e, struct ip_vs_app, a_list);
                list_for_each_entry(inc, &app->incs_list, a_list) {
                        return inc;
                }
        }
        return NULL;
}

static void ip_vs_app_seq_stop(struct seq_file *seq, void *v)
{
        mutex_unlock(&__ip_vs_app_mutex);
}

static int ip_vs_app_seq_show(struct seq_file *seq, void *v)
{
        if (v == SEQ_START_TOKEN)
                seq_puts(seq, "prot port    usecnt name\n");
        else {
                const struct ip_vs_app *inc = v;

                seq_printf(seq, "%-3s  %-7u %-6d %-17s\n",
                           ip_vs_proto_name(inc->protocol),
                           ntohs(inc->port),
                           atomic_read(&inc->usecnt),
                           inc->name);
        }
        return 0;
}

static const struct seq_operations ip_vs_app_seq_ops = {
        .start = ip_vs_app_seq_start,
        .next  = ip_vs_app_seq_next,
        .stop  = ip_vs_app_seq_stop,
        .show  = ip_vs_app_seq_show,
};

static int ip_vs_app_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &ip_vs_app_seq_ops);
}

static const struct file_operations ip_vs_app_fops = {
        .owner   = THIS_MODULE,
        .open    = ip_vs_app_open,
        .read    = seq_read,
        .llseek  = seq_lseek,
        .release = seq_release,
};
#endif


/*
 *      Replace a segment of data with a new segment
 */
int ip_vs_skb_replace(struct sk_buff *skb, gfp_t pri,
                      char *o_buf, int o_len, char *n_buf, int n_len)
{
        int diff;
        int o_offset;
        int o_left;

        EnterFunction(9);

        diff = n_len - o_len;
        o_offset = o_buf - (char *)skb->data;
        /* The length of left data after o_buf+o_len in the skb data */
        o_left = skb->len - (o_offset + o_len);

        if (diff <= 0) {
                memmove(o_buf + n_len, o_buf + o_len, o_left);
                memcpy(o_buf, n_buf, n_len);
                skb_trim(skb, skb->len + diff);
        } else if (diff <= skb_tailroom(skb)) {
                skb_put(skb, diff);
                memmove(o_buf + n_len, o_buf + o_len, o_left);
                memcpy(o_buf, n_buf, n_len);
        } else {
                if (pskb_expand_head(skb, skb_headroom(skb), diff, pri))
                        return -ENOMEM;
                skb_put(skb, diff);
                memmove(skb->data + o_offset + n_len,
                        skb->data + o_offset + o_len, o_left);
                skb_copy_to_linear_data_offset(skb, o_offset, n_buf, n_len);
        }

        /* must update the iph total length here */
        ip_hdr(skb)->tot_len = htons(skb->len);

        LeaveFunction(9);
        return 0;
}


int __init ip_vs_app_init(void)
{
        /* we will replace it with proc_net_ipvs_create() soon */
        proc_net_fops_create(&init_net, "ip_vs_app", 0, &ip_vs_app_fops);
        return 0;
}


void ip_vs_app_cleanup(void)
{
        proc_net_remove(&init_net, "ip_vs_app");
}