// 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);

  
  /* This is slow, but it's simple. --RR */
  static char *ftp_buffer;
  
  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 (*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
  ",
  				 len, i, *data);

  			return 0;
  		}
  	}

  	pr_debug("Failed to fill %u numbers separated by %c
  ",
  		 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
  ", 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.
  ");

  			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
  ");

  		return 0;
  	}
  	delim = data[0];
  	if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {

  		pr_debug("try_eprt: invalid delimiter.
  ");

  		return 0;
  	}
  
  	if ((cmd->l3num == PF_INET && data[1] != '1') ||
  	    (cmd->l3num == PF_INET6 && data[1] != '2')) {

  		pr_debug("EPRT: invalid protocol number.
  ");

  		return 0;
  	}

  	pr_debug("EPRT: Got %c%c%c
  ", 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!
  ");

  	/* 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
  ", 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!
  ");

  	/* 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!
  ", skip);

  
  	*numoff = i;

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

  	if (!*numlen)
  		return -1;

  	pr_debug("Match succeeded!
  ");

  	return 1;
  }
  
  /* Look up to see if we're just after a 
  . */

  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
  ", ctinfo);

  		return NF_ACCEPT;
  	}

  	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)
  ", dataoff,

  			 skb->len);

  		return NF_ACCEPT;
  	}

  	datalen = skb->len - dataoff;

  
  	spin_lock_bh(&nf_ftp_lock);

  	fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);

  	BUG_ON(fb_ptr == NULL);
  
  	ends_in_nl = (fb_ptr[datalen - 1] == '
  ');
  	seq = ntohl(th->seq) + datalen;
  
  	/* Look up to see if we're just after a 
  . */
  	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 
  , update ftp info. */

  		pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)
  ",
  			 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)
  ",
  		 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
  ",

  				 &cmd.u3.ip,
  				 &ct->tuplehash[dir].tuple.src.u3.ip);

  		} else {

  			pr_debug("NOT RECORDING: %pI6 != %pI6
  ",

  				 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 
  , 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);

  	kfree(ftp_buffer);
  }

  static int __init nf_conntrack_ftp_init(void)

  {

  	int i, ret = 0;

  	NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));

  	ftp_buffer = kmalloc(65536, GFP_KERNEL);
  	if (!ftp_buffer)
  		return -ENOMEM;
  
  	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
  ");
  		kfree(ftp_buffer);
  		return ret;

  	}
  
  	return 0;
  }

  module_init(nf_conntrack_ftp_init);
  module_exit(nf_conntrack_ftp_fini);