// SPDX-License-Identifier: GPL-2.0-only
/* FTP extension for connection tracking. */
/* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2004 Netfilter Core Team <[email protected]>
* (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
* (C) 2006-2012 Patrick McHardy <[email protected]>
*/
#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 <[email protected]>");
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 (*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
<[email protected]> 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);
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