// SPDX-License-Identifier: GPL-2.0-only
/* FTP extension for connection tracking. */

/* (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) 2006-2012 Patrick McHardy <kaber@trash.net>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/netfilter.h>
#include <linux/ip.h>
#include <linux/slab.h>
#include <linux/ipv6.h>
#include <linux/ctype.h>
#include <linux/inet.h>
#include <net/checksum.h>
#include <net/tcp.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <linux/netfilter/nf_conntrack_ftp.h>

#define HELPER_NAME "ftp"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
MODULE_DESCRIPTION("ftp connection tracking helper");
MODULE_ALIAS("ip_conntrack_ftp");
MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
static DEFINE_SPINLOCK(nf_ftp_lock);

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

static bool loose;
module_param(loose, bool, 0600);

unsigned int (__rcu *nf_nat_ftp_hook)(struct sk_buff *skb,
                                      enum ip_conntrack_info ctinfo,
                                      enum nf_ct_ftp_type type,
                                      unsigned int protoff,
                                      unsigned int matchoff,
                                      unsigned int matchlen,
                                      struct nf_conntrack_expect *exp);
EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);

static int try_rfc959(const char *, size_t, struct nf_conntrack_man *,
                      char, unsigned int *);
static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *,
                       char, unsigned int *);
static int try_eprt(const char *, size_t, struct nf_conntrack_man *,
                    char, unsigned int *);
static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
                             char, unsigned int *);

static struct ftp_search {
        const char *pattern;
        size_t plen;
        char skip;
        char term;
        enum nf_ct_ftp_type ftptype;
        int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *);
} search[IP_CT_DIR_MAX][2] = {
        [IP_CT_DIR_ORIGINAL] = {
                {
                        .pattern        = "PORT",
                        .plen           = sizeof("PORT") - 1,
                        .skip           = ' ',
                        .term           = '\r',
                        .ftptype        = NF_CT_FTP_PORT,
                        .getnum         = try_rfc959,
                },
                {
                        .pattern        = "EPRT",
                        .plen           = sizeof("EPRT") - 1,
                        .skip           = ' ',
                        .term           = '\r',
                        .ftptype        = NF_CT_FTP_EPRT,
                        .getnum         = try_eprt,
                },
        },
        [IP_CT_DIR_REPLY] = {
                {
                        .pattern        = "227 ",
                        .plen           = sizeof("227 ") - 1,
                        .ftptype        = NF_CT_FTP_PASV,
                        .getnum         = try_rfc1123,
                },
                {
                        .pattern        = "229 ",
                        .plen           = sizeof("229 ") - 1,
                        .skip           = '(',
                        .term           = ')',
                        .ftptype        = NF_CT_FTP_EPSV,
                        .getnum         = try_epsv_response,
                },
        },
};

static int
get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
{
        const char *end;
        int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
        if (ret > 0)
                return (int)(end - src);
        return 0;
}

static int try_number(const char *data, size_t dlen, u_int32_t array[],
                      int array_size, char sep, char term)
{
        u_int32_t i, len;

        memset(array, 0, sizeof(array[0])*array_size);

        /* Keep data pointing at next char. */
        for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
                if (*data >= '0' && *data <= '9') {
                        array[i] = array[i]*10 + *data - '0';
                }
                else if (*data == sep)
                        i++;
                else {
                        /* Unexpected character; true if it's the
                           terminator (or we don't care about one)
                           and we're finished. */
                        if ((*data == term || !term) && i == array_size - 1)
                                return len;

                        pr_debug("Char %u (got %u nums) `%u' unexpected\n",
                                 len, i, *data);
                        return 0;
                }
        }
        pr_debug("Failed to fill %u numbers separated by %c\n",
                 array_size, sep);
        return 0;
}

/* Returns 0, or length of numbers: 192,168,1,1,5,6 */
static int try_rfc959(const char *data, size_t dlen,
                      struct nf_conntrack_man *cmd, char term,
                      unsigned int *offset)
{
        int length;
        u_int32_t array[6];

        length = try_number(data, dlen, array, 6, ',', term);
        if (length == 0)
                return 0;

        cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) |
                                    (array[2] << 8) | array[3]);
        cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
        return length;
}

/*
 * From RFC 1123:
 * The format of the 227 reply to a PASV command is not
 * well standardized.  In particular, an FTP client cannot
 * assume that the parentheses shown on page 40 of RFC-959
 * will be present (and in fact, Figure 3 on page 43 omits
 * them).  Therefore, a User-FTP program that interprets
 * the PASV reply must scan the reply for the first digit
 * of the host and port numbers.
 */
static int try_rfc1123(const char *data, size_t dlen,
                       struct nf_conntrack_man *cmd, char term,
                       unsigned int *offset)
{
        int i;
        for (i = 0; i < dlen; i++)
                if (isdigit(data[i]))
                        break;

        if (i == dlen)
                return 0;

        *offset += i;

        return try_rfc959(data + i, dlen - i, cmd, 0, offset);
}

/* Grab port: number up to delimiter */
static int get_port(const char *data, int start, size_t dlen, char delim,
                    __be16 *port)
{
        u_int16_t tmp_port = 0;
        int i;

        for (i = start; i < dlen; i++) {
                /* Finished? */
                if (data[i] == delim) {
                        if (tmp_port == 0)
                                break;
                        *port = htons(tmp_port);
                        pr_debug("get_port: return %d\n", tmp_port);
                        return i + 1;
                }
                else if (data[i] >= '0' && data[i] <= '9')
                        tmp_port = tmp_port*10 + data[i] - '0';
                else { /* Some other crap */
                        pr_debug("get_port: invalid char.\n");
                        break;
                }
        }
        return 0;
}

/* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
                    char term, unsigned int *offset)
{
        char delim;
        int length;

        /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
           then delimiter again. */
        if (dlen <= 3) {
                pr_debug("EPRT: too short\n");
                return 0;
        }
        delim = data[0];
        if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
                pr_debug("try_eprt: invalid delimiter.\n");
                return 0;
        }

        if ((cmd->l3num == PF_INET && data[1] != '1') ||
            (cmd->l3num == PF_INET6 && data[1] != '2')) {
                pr_debug("EPRT: invalid protocol number.\n");
                return 0;
        }

        pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);

        if (data[1] == '1') {
                u_int32_t array[4];

                /* Now we have IP address. */
                length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
                if (length != 0)
                        cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
                                           | (array[2] << 8) | array[3]);
        } else {
                /* Now we have IPv6 address. */
                length = get_ipv6_addr(data + 3, dlen - 3,
                                       (struct in6_addr *)cmd->u3.ip6, delim);
        }

        if (length == 0)
                return 0;
        pr_debug("EPRT: Got IP address!\n");
        /* Start offset includes initial "|1|", and trailing delimiter */
        return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
}

/* Returns 0, or length of numbers: |||6446| */
static int try_epsv_response(const char *data, size_t dlen,
                             struct nf_conntrack_man *cmd, char term,
                             unsigned int *offset)
{
        char delim;

        /* Three delimiters. */
        if (dlen <= 3) return 0;
        delim = data[0];
        if (isdigit(delim) || delim < 33 || delim > 126 ||
            data[1] != delim || data[2] != delim)
                return 0;

        return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
}

/* Return 1 for match, 0 for accept, -1 for partial. */
static int find_pattern(const char *data, size_t dlen,
                        const char *pattern, size_t plen,
                        char skip, char term,
                        unsigned int *numoff,
                        unsigned int *numlen,
                        struct nf_conntrack_man *cmd,
                        int (*getnum)(const char *, size_t,
                                      struct nf_conntrack_man *, char,
                                      unsigned int *))
{
        size_t i = plen;

        pr_debug("find_pattern `%s': dlen = %zu\n", pattern, dlen);

        if (dlen <= plen) {
                /* Short packet: try for partial? */
                if (strncasecmp(data, pattern, dlen) == 0)
                        return -1;
                else return 0;
        }

        if (strncasecmp(data, pattern, plen) != 0)
                return 0;

        pr_debug("Pattern matches!\n");
        /* Now we've found the constant string, try to skip
           to the 'skip' character */
        if (skip) {
                for (i = plen; data[i] != skip; i++)
                        if (i == dlen - 1) return -1;

                /* Skip over the last character */
                i++;
        }

        pr_debug("Skipped up to 0x%hhx delimiter!\n", skip);

        *numoff = i;
        *numlen = getnum(data + i, dlen - i, cmd, term, numoff);
        if (!*numlen)
                return -1;

        pr_debug("Match succeeded!\n");
        return 1;
}

/* Look up to see if we're just after a \n. */
static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
{
        unsigned int i;

        for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
                if (info->seq_aft_nl[dir][i] == seq)
                        return 1;
        return 0;
}

/* We don't update if it's older than what we have. */
static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
                          struct nf_ct_ftp_master *info, int dir,
                          struct sk_buff *skb)
{
        unsigned int i, oldest;

        /* Look for oldest: if we find exact match, we're done. */
        for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
                if (info->seq_aft_nl[dir][i] == nl_seq)
                        return;
        }

        if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
                info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
        } else {
                if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1]))
                        oldest = 0;
                else
                        oldest = 1;

                if (after(nl_seq, info->seq_aft_nl[dir][oldest]))
                        info->seq_aft_nl[dir][oldest] = nl_seq;
        }
}

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;
        const char *fb_ptr;
        int ret;
        u32 seq;
        int dir = CTINFO2DIR(ctinfo);
        unsigned int matchlen, matchoff;
        struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct);
        struct nf_conntrack_expect *exp;
        union nf_inet_addr *daddr;
        struct nf_conntrack_man cmd = {};
        unsigned int i;
        int found = 0, ends_in_nl;
        typeof(nf_nat_ftp_hook) nf_nat_ftp;

        /* Until there's been traffic both ways, don't look in packets. */
        if (ctinfo != IP_CT_ESTABLISHED &&
            ctinfo != IP_CT_ESTABLISHED_REPLY) {
                pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
                return NF_ACCEPT;
        }

        if (unlikely(skb_linearize(skb)))
                return NF_DROP;

        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
        if (th == NULL)
                return NF_ACCEPT;

        dataoff = protoff + th->doff * 4;
        /* No data? */
        if (dataoff >= skb->len) {
                pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
                         skb->len);
                return NF_ACCEPT;
        }
        datalen = skb->len - dataoff;

        /* seqadj (nat) uses ct->lock internally, nf_nat_ftp would cause deadlock */
        spin_lock_bh(&nf_ftp_lock);
        fb_ptr = skb->data + dataoff;

        ends_in_nl = (fb_ptr[datalen - 1] == '\n');
        seq = ntohl(th->seq) + datalen;

        /* Look up to see if we're just after a \n. */
        if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
                /* We're picking up this, clear flags and let it continue */
                if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
                        ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
                        goto skip_nl_seq;
                }

                /* Now if this ends in \n, update ftp info. */
                pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
                         ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
                         ct_ftp_info->seq_aft_nl[dir][0],
                         ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
                         ct_ftp_info->seq_aft_nl[dir][1]);
                ret = NF_ACCEPT;
                goto out_update_nl;
        }

skip_nl_seq:
        /* Initialize IP/IPv6 addr to expected address (it's not mentioned
           in EPSV responses) */
        cmd.l3num = nf_ct_l3num(ct);
        memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
               sizeof(cmd.u3.all));

        for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
                found = find_pattern(fb_ptr, datalen,
                                     search[dir][i].pattern,
                                     search[dir][i].plen,
                                     search[dir][i].skip,
                                     search[dir][i].term,
                                     &matchoff, &matchlen,
                                     &cmd,
                                     search[dir][i].getnum);
                if (found) break;
        }
        if (found == -1) {
                /* We don't usually drop packets.  After all, this is
                   connection tracking, not packet filtering.
                   However, it is necessary for accurate tracking in
                   this case. */
                nf_ct_helper_log(skb, ct, "partial matching of `%s'",
                                 search[dir][i].pattern);
                ret = NF_DROP;
                goto out;
        } else if (found == 0) { /* No match */
                ret = NF_ACCEPT;
                goto out_update_nl;
        }

        pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
                 matchlen, fb_ptr + matchoff,
                 matchlen, ntohl(th->seq) + matchoff);

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

        /* We refer to the reverse direction ("!dir") tuples here,
         * because we're expecting something in the other direction.
         * Doesn't matter unless NAT is happening.  */
        daddr = &ct->tuplehash[!dir].tuple.dst.u3;

        /* Update the ftp info */
        if ((cmd.l3num == nf_ct_l3num(ct)) &&
            memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
                     sizeof(cmd.u3.all))) {
                /* Enrico Scholz's passive FTP to partially RNAT'd ftp
                   server: it really wants us to connect to a
                   different IP address.  Simply don't record it for
                   NAT. */
                if (cmd.l3num == PF_INET) {
                        pr_debug("NOT RECORDING: %pI4 != %pI4\n",
                                 &cmd.u3.ip,
                                 &ct->tuplehash[dir].tuple.src.u3.ip);
                } else {
                        pr_debug("NOT RECORDING: %pI6 != %pI6\n",
                                 cmd.u3.ip6,
                                 ct->tuplehash[dir].tuple.src.u3.ip6);
                }

                /* Thanks to Cristiano Lincoln Mattos
                   <lincoln@cesar.org.br> for reporting this potential
                   problem (DMZ machines opening holes to internal
                   networks, or the packet filter itself). */
                if (!loose) {
                        ret = NF_ACCEPT;
                        goto out_put_expect;
                }
                daddr = &cmd.u3;
        }

        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
                          &ct->tuplehash[!dir].tuple.src.u3, daddr,
                          IPPROTO_TCP, NULL, &cmd.u.tcp.port);

        /* Now, NAT might want to mangle the packet, and register the
         * (possibly changed) expectation itself. */
        nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
        if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
                ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
                                 protoff, matchoff, matchlen, exp);
        else {
                /* 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;
                } else
                        ret = NF_ACCEPT;
        }

out_put_expect:
        nf_ct_expect_put(exp);

out_update_nl:
        /* Now if this ends in \n, update ftp info.  Seq may have been
         * adjusted by NAT code. */
        if (ends_in_nl)
                update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
 out:
        spin_unlock_bh(&nf_ftp_lock);
        return ret;
}

static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
{
        struct nf_ct_ftp_master *ftp = nfct_help_data(ct);

        /* This conntrack has been injected from user-space, always pick up
         * sequence tracking. Otherwise, the first FTP command after the
         * failover breaks.
         */
        ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
        ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
        return 0;
}

static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly;

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

static void __exit nf_conntrack_ftp_fini(void)
{
        nf_conntrack_helpers_unregister(ftp, ports_c * 2);
}

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

        NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));

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

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

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

        return 0;
}

module_init(nf_conntrack_ftp_init);
module_exit(nf_conntrack_ftp_fini);