// SPDX-License-Identifier: GPL-2.0-only
/* SANE connection tracking helper
 * (SANE = Scanner Access Now Easy)
 * For documentation about the SANE network protocol see
 * http://www.sane-project.org/html/doc015.html
 */

/* Copyright (C) 2007 Red Hat, Inc.
 * Author: Michal Schmidt <mschmidt@redhat.com>
 * Based on the FTP conntrack helper (net/netfilter/nf_conntrack_ftp.c):
 *  (C) 1999-2001 Paul `Rusty' Russell
 *  (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
 *  (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
 *  (C) 2003 Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/netfilter.h>
#include <linux/slab.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_sane.h>

#define HELPER_NAME "sane"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
MODULE_DESCRIPTION("SANE connection tracking helper");
MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);

#define MAX_PORTS 8
static u_int16_t ports[MAX_PORTS];
static unsigned int ports_c;
module_param_array(ports, ushort, &ports_c, 0400);

struct sane_request {
        __be32 RPC_code;
#define SANE_NET_START      7   /* RPC code */

        __be32 handle;
};

struct sane_reply_net_start {
        __be32 status;
#define SANE_STATUS_SUCCESS 0

        __be16 zero;
        __be16 port;
        /* other fields aren't interesting for conntrack */
};

static int help(struct sk_buff *skb,
                unsigned int protoff,
                struct nf_conn *ct,
                enum ip_conntrack_info ctinfo)
{
        unsigned int dataoff, datalen;
        const struct tcphdr *th;
        struct tcphdr _tcph;
        int ret = NF_ACCEPT;
        int dir = CTINFO2DIR(ctinfo);
        struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
        struct nf_conntrack_expect *exp;
        struct nf_conntrack_tuple *tuple;
        struct sane_reply_net_start *reply;
        union {
                struct sane_request req;
                struct sane_reply_net_start repl;
        } buf;

        /* Until there's been traffic both ways, don't look in packets. */
        if (ctinfo != IP_CT_ESTABLISHED &&
            ctinfo != IP_CT_ESTABLISHED_REPLY)
                return NF_ACCEPT;

        /* Not a full tcp header? */
        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
        if (th == NULL)
                return NF_ACCEPT;

        /* No data? */
        dataoff = protoff + th->doff * 4;
        if (dataoff >= skb->len)
                return NF_ACCEPT;

        datalen = skb->len - dataoff;
        if (dir == IP_CT_DIR_ORIGINAL) {
                const struct sane_request *req;

                if (datalen != sizeof(struct sane_request))
                        return NF_ACCEPT;

                req = skb_header_pointer(skb, dataoff, datalen, &buf.req);
                if (!req)
                        return NF_ACCEPT;

                if (req->RPC_code != htonl(SANE_NET_START)) {
                        /* Not an interesting command */
                        WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
                        return NF_ACCEPT;
                }

                /* We're interested in the next reply */
                WRITE_ONCE(ct_sane_info->state, SANE_STATE_START_REQUESTED);
                return NF_ACCEPT;
        }

        /* IP_CT_DIR_REPLY */

        /* Is it a reply to an uninteresting command? */
        if (READ_ONCE(ct_sane_info->state) != SANE_STATE_START_REQUESTED)
                return NF_ACCEPT;

        /* It's a reply to SANE_NET_START. */
        WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);

        if (datalen < sizeof(struct sane_reply_net_start)) {
                pr_debug("NET_START reply too short\n");
                return NF_ACCEPT;
        }

        datalen = sizeof(struct sane_reply_net_start);

        reply = skb_header_pointer(skb, dataoff, datalen, &buf.repl);
        if (!reply)
                return NF_ACCEPT;

        if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
                /* saned refused the command */
                pr_debug("unsuccessful SANE_STATUS = %u\n",
                         ntohl(reply->status));
                return NF_ACCEPT;
        }

        /* Invalid saned reply? Ignore it. */
        if (reply->zero != 0)
                return NF_ACCEPT;

        exp = nf_ct_expect_alloc(ct);
        if (exp == NULL) {
                nf_ct_helper_log(skb, ct, "cannot alloc expectation");
                return NF_DROP;
        }

        tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
                          &tuple->src.u3, &tuple->dst.u3,
                          IPPROTO_TCP, NULL, &reply->port);

        pr_debug("expect: ");
        nf_ct_dump_tuple(&exp->tuple);

        /* Can't expect this?  Best to drop packet now. */
        if (nf_ct_expect_related(exp, 0) != 0) {
                nf_ct_helper_log(skb, ct, "cannot add expectation");
                ret = NF_DROP;
        }

        nf_ct_expect_put(exp);
        return ret;
}

static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;

static const struct nf_conntrack_expect_policy sane_exp_policy = {
        .max_expected   = 1,
        .timeout        = 5 * 60,
};

static void __exit nf_conntrack_sane_fini(void)
{
        nf_conntrack_helpers_unregister(sane, ports_c * 2);
}

static int __init nf_conntrack_sane_init(void)
{
        int i, ret = 0;

        NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));

        if (ports_c == 0)
                ports[ports_c++] = SANE_PORT;

        /* FIXME should be configurable whether IPv4 and IPv6 connections
                 are tracked or not - YK */
        for (i = 0; i < ports_c; i++) {
                nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP,
                                  HELPER_NAME, SANE_PORT, ports[i], ports[i],
                                  &sane_exp_policy, 0, help, NULL,
                                  THIS_MODULE);
                nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP,
                                  HELPER_NAME, SANE_PORT, ports[i], ports[i],
                                  &sane_exp_policy, 0, help, NULL,
                                  THIS_MODULE);
        }

        ret = nf_conntrack_helpers_register(sane, ports_c * 2);
        if (ret < 0) {
                pr_err("failed to register helpers\n");
                return ret;
        }

        return 0;
}

module_init(nf_conntrack_sane_init);
module_exit(nf_conntrack_sane_fini);