IPVS: make FTP work with full NAT support

Use nf_conntrack/nf_nat code to do the packet mangling and the TCP
sequence adjusting.  The function 'ip_vs_skb_replace' is now dead
code, so it is removed.

To SNAT FTP, use something like:

% iptables -t nat -A POSTROUTING -m ipvs --vaddr 192.168.100.30/32 \
    --vport 21 -j SNAT --to-source 192.168.10.10
and for the data connections in passive mode:

% iptables -t nat -A POSTROUTING -m ipvs --vaddr 192.168.100.30/32 \
    --vportctl 21 -j SNAT --to-source 192.168.10.10
using '-m state --state RELATED' would also works.

Make sure the kernel modules ip_vs_ftp, nf_conntrack_ftp, and
nf_nat_ftp are loaded.

[ up-port and minor fixes by Simon Horman <horms@verge.net.au> ]
Signed-off-by: Hannes Eder <heder@google.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Patrick McHardy <kaber@trash.net>

4 files changed, 165 insertions, 57 deletions

diff --git a/net/netfilter/ipvs/Kconfig b/net/netfilter/ipvs/Kconfig
index 366244492ac7..be10f6526042 100644
--- a/net/netfilter/ipvs/Kconfig
+++ b/net/netfilter/ipvs/Kconfig
@@ -235,7 +235,7 @@ comment 'IPVS application helper'
 
 config  IP_VS_FTP
         tristate "FTP protocol helper"
-        depends on IP_VS_PROTO_TCP
+        depends on IP_VS_PROTO_TCP && NF_NAT
         ---help---
           FTP is a protocol that transfers IP address and/or port number in
           the payload. In the virtual server via Network Address Translation,
diff --git a/net/netfilter/ipvs/ip_vs_app.c b/net/netfilter/ipvs/ip_vs_app.c
index 1cb0e834f8ff..e76f87f4aca8 100644
--- a/net/netfilter/ipvs/ip_vs_app.c
+++ b/net/netfilter/ipvs/ip_vs_app.c
@@ -569,49 +569,6 @@ static const struct file_operations ip_vs_app_fops = {
 };
 #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 */
diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 58f82dfc950a..4f8ddba48011 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -54,7 +54,6 @@
 
 EXPORT_SYMBOL(register_ip_vs_scheduler);
 EXPORT_SYMBOL(unregister_ip_vs_scheduler);
-EXPORT_SYMBOL(ip_vs_skb_replace);
 EXPORT_SYMBOL(ip_vs_proto_name);
 EXPORT_SYMBOL(ip_vs_conn_new);
 EXPORT_SYMBOL(ip_vs_conn_in_get);
diff --git a/net/netfilter/ipvs/ip_vs_ftp.c b/net/netfilter/ipvs/ip_vs_ftp.c
index 2ae747a376a5..f228a17ec649 100644
--- a/net/netfilter/ipvs/ip_vs_ftp.c
+++ b/net/netfilter/ipvs/ip_vs_ftp.c
@@ -20,6 +20,17 @@
  *
  * Author:      Wouter Gadeyne
  *
+ *
+ * Code for ip_vs_expect_related and ip_vs_expect_callback is taken from
+ * http://www.ssi.bg/~ja/nfct/:
+ *
+ * ip_vs_nfct.c:        Netfilter connection tracking support for IPVS
+ *
+ * Portions Copyright (C) 2001-2002
+ * Antefacto Ltd, 181 Parnell St, Dublin 1, Ireland.
+ *
+ * Portions Copyright (C) 2003-2008
+ * Julian Anastasov
  */
 
 #define KMSG_COMPONENT "IPVS"
@@ -32,6 +43,9 @@
 #include <linux/in.h>
 #include <linux/ip.h>
 #include <linux/netfilter.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <net/netfilter/nf_nat_helper.h>
 #include <linux/gfp.h>
 #include <net/protocol.h>
 #include <net/tcp.h>
@@ -43,6 +57,16 @@
 #define SERVER_STRING "227 Entering Passive Mode ("
 #define CLIENT_STRING "PORT "
 
+#define FMT_TUPLE       "%pI4:%u->%pI4:%u/%u"
+#define ARG_TUPLE(T)    &(T)->src.u3.ip, ntohs((T)->src.u.all), \
+                        &(T)->dst.u3.ip, ntohs((T)->dst.u.all), \
+                        (T)->dst.protonum
+
+#define FMT_CONN        "%pI4:%u->%pI4:%u->%pI4:%u/%u:%u"
+#define ARG_CONN(C)     &((C)->caddr.ip), ntohs((C)->cport), \
+                        &((C)->vaddr.ip), ntohs((C)->vport), \
+                        &((C)->daddr.ip), ntohs((C)->dport), \
+                        (C)->protocol, (C)->state
 
 /*
  * List of ports (up to IP_VS_APP_MAX_PORTS) to be handled by helper
@@ -123,6 +147,119 @@ static int ip_vs_ftp_get_addrport(char *data, char *data_limit,
         return 1;
 }
 
+/*
+ * Called from init_conntrack() as expectfn handler.
+ */
+static void
+ip_vs_expect_callback(struct nf_conn *ct,
+                      struct nf_conntrack_expect *exp)
+{
+        struct nf_conntrack_tuple *orig, new_reply;
+        struct ip_vs_conn *cp;
+
+        if (exp->tuple.src.l3num != PF_INET)
+                return;
+
+        /*
+         * We assume that no NF locks are held before this callback.
+         * ip_vs_conn_out_get and ip_vs_conn_in_get should match their
+         * expectations even if they use wildcard values, now we provide the
+         * actual values from the newly created original conntrack direction.
+         * The conntrack is confirmed when packet reaches IPVS hooks.
+         */
+
+        /* RS->CLIENT */
+        orig = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
+        cp = ip_vs_conn_out_get(exp->tuple.src.l3num, orig->dst.protonum,
+                                &orig->src.u3, orig->src.u.tcp.port,
+                                &orig->dst.u3, orig->dst.u.tcp.port);
+        if (cp) {
+                /* Change reply CLIENT->RS to CLIENT->VS */
+                new_reply = ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+                IP_VS_DBG(7, "%s(): ct=%p, status=0x%lX, tuples=" FMT_TUPLE ", "
+                          FMT_TUPLE ", found inout cp=" FMT_CONN "\n",
+                          __func__, ct, ct->status,
+                          ARG_TUPLE(orig), ARG_TUPLE(&new_reply),
+                          ARG_CONN(cp));
+                new_reply.dst.u3 = cp->vaddr;
+                new_reply.dst.u.tcp.port = cp->vport;
+                IP_VS_DBG(7, "%s(): ct=%p, new tuples=" FMT_TUPLE ", " FMT_TUPLE
+                          ", inout cp=" FMT_CONN "\n",
+                          __func__, ct,
+                          ARG_TUPLE(orig), ARG_TUPLE(&new_reply),
+                          ARG_CONN(cp));
+                goto alter;
+        }
+
+        /* CLIENT->VS */
+        cp = ip_vs_conn_in_get(exp->tuple.src.l3num, orig->dst.protonum,
+                               &orig->src.u3, orig->src.u.tcp.port,
+                               &orig->dst.u3, orig->dst.u.tcp.port);
+        if (cp) {
+                /* Change reply VS->CLIENT to RS->CLIENT */
+                new_reply = ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+                IP_VS_DBG(7, "%s(): ct=%p, status=0x%lX, tuples=" FMT_TUPLE ", "
+                          FMT_TUPLE ", found outin cp=" FMT_CONN "\n",
+                          __func__, ct, ct->status,
+                          ARG_TUPLE(orig), ARG_TUPLE(&new_reply),
+                          ARG_CONN(cp));
+                new_reply.src.u3 = cp->daddr;
+                new_reply.src.u.tcp.port = cp->dport;
+                IP_VS_DBG(7, "%s(): ct=%p, new tuples=" FMT_TUPLE ", "
+                          FMT_TUPLE ", outin cp=" FMT_CONN "\n",
+                          __func__, ct,
+                          ARG_TUPLE(orig), ARG_TUPLE(&new_reply),
+                          ARG_CONN(cp));
+                goto alter;
+        }
+
+        IP_VS_DBG(7, "%s(): ct=%p, status=0x%lX, tuple=" FMT_TUPLE
+                  " - unknown expect\n",
+                  __func__, ct, ct->status, ARG_TUPLE(orig));
+        return;
+
+alter:
+        /* Never alter conntrack for non-NAT conns */
+        if (IP_VS_FWD_METHOD(cp) == IP_VS_CONN_F_MASQ)
+                nf_conntrack_alter_reply(ct, &new_reply);
+        ip_vs_conn_put(cp);
+        return;
+}
+
+/*
+ * Create NF conntrack expectation with wildcard (optional) source port.
+ * Then the default callback function will alter the reply and will confirm
+ * the conntrack entry when the first packet comes.
+ */
+static void
+ip_vs_expect_related(struct sk_buff *skb, struct nf_conn *ct,
+                     struct ip_vs_conn *cp, u_int8_t proto,
+                     const __be16 *port, int from_rs)
+{
+        struct nf_conntrack_expect *exp;
+
+        BUG_ON(!ct || ct == &nf_conntrack_untracked);
+
+        exp = nf_ct_expect_alloc(ct);
+        if (!exp)
+                return;
+
+        if (from_rs)
+                nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
+                                  nf_ct_l3num(ct), &cp->daddr, &cp->caddr,
+                                  proto, port, &cp->cport);
+        else
+                nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
+                                  nf_ct_l3num(ct), &cp->caddr, &cp->vaddr,
+                                  proto, port, &cp->vport);
+
+        exp->expectfn = ip_vs_expect_callback;
+
+        IP_VS_DBG(7, "%s(): ct=%p, expect tuple=" FMT_TUPLE "\n",
+                  __func__, ct, ARG_TUPLE(&exp->tuple));
+        nf_ct_expect_related(exp);
+        nf_ct_expect_put(exp);
+}
 
 /*
  * Look at outgoing ftp packets to catch the response to a PASV command
@@ -149,7 +286,9 @@ static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
         struct ip_vs_conn *n_cp;
         char buf[24];           /* xxx.xxx.xxx.xxx,ppp,ppp\000 */
         unsigned buf_len;
-        int ret;
+        int ret = 0;
+        enum ip_conntrack_info ctinfo;
+        struct nf_conn *ct;
 
 #ifdef CONFIG_IP_VS_IPV6
         /* This application helper doesn't work with IPv6 yet,
@@ -219,19 +358,26 @@ static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
 
                 buf_len = strlen(buf);
 
+                ct = nf_ct_get(skb, &ctinfo);
+                if (ct && !nf_ct_is_untracked(ct)) {
+                        /* If mangling fails this function will return 0
+                         * which will cause the packet to be dropped.
+                         * Mangling can only fail under memory pressure,
+                         * hopefully it will succeed on the retransmitted
+                         * packet.
+                         */
+                        ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
+                                                       start-data, end-start,
+                                                       buf, buf_len);
+                        if (ret)
+                                ip_vs_expect_related(skb, ct, n_cp,
+                                                     IPPROTO_TCP, NULL, 0);
+                }
+
                 /*
-                 * Calculate required delta-offset to keep TCP happy
+                 * Not setting 'diff' is intentional, otherwise the sequence
+                 * would be adjusted twice.
                  */
-                *diff = buf_len - (end-start);
-
-                if (*diff == 0) {
-                        /* simply replace it with new passive address */
-                        memcpy(start, buf, buf_len);
-                        ret = 1;
-                } else {
-                        ret = !ip_vs_skb_replace(skb, GFP_ATOMIC, start,
-                                          end-start, buf, buf_len);
-                }
 
                 cp->app_data = NULL;
                 ip_vs_tcp_conn_listen(n_cp);
@@ -263,6 +409,7 @@ static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
         union nf_inet_addr to;
         __be16 port;
         struct ip_vs_conn *n_cp;
+        struct nf_conn *ct;
 
 #ifdef CONFIG_IP_VS_IPV6
         /* This application helper doesn't work with IPv6 yet,
@@ -349,6 +496,11 @@ static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
                 ip_vs_control_add(n_cp, cp);
         }
 
+        ct = (struct nf_conn *)skb->nfct;
+        if (ct && ct != &nf_conntrack_untracked)
+                ip_vs_expect_related(skb, ct, n_cp,
+                                     IPPROTO_TCP, &n_cp->dport, 1);
+
         /*
          *      Move tunnel to listen state
          */