[NETFILTER]: Add SANE connection tracking helper

This is nf_conntrack_sane, a netfilter connection tracking helper module
for the SANE protocol used by the 'saned' daemon to make scanners available
via network. The SANE protocol uses separate control & data connections,
similar to passive FTP. The helper module is needed to recognize the data
connection as RELATED to the control one.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 256 insertions, 0 deletions

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 80107d4909c5..614c92c17835 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -235,6 +235,19 @@ config NF_CONNTRACK_PPTP
 
           To compile it as a module, choose M here.  If unsure, say N.
 
+config NF_CONNTRACK_SANE
+        tristate "SANE protocol support (EXPERIMENTAL)"
+        depends on EXPERIMENTAL && NF_CONNTRACK
+        help
+          SANE is a protocol for remote access to scanners as implemented
+          by the 'saned' daemon. Like FTP, it uses separate control and
+          data connections.
+
+          With this module you can support SANE on a connection tracking
+          firewall.
+
+          To compile it as a module, choose M here.  If unsure, say N.
+
 config NF_CONNTRACK_SIP
         tristate "SIP protocol support (EXPERIMENTAL)"
         depends on EXPERIMENTAL && NF_CONNTRACK
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 5dc5574f7e99..5054b0ff8096 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_NF_CONNTRACK_H323) += nf_conntrack_h323.o
 obj-$(CONFIG_NF_CONNTRACK_IRC) += nf_conntrack_irc.o
 obj-$(CONFIG_NF_CONNTRACK_NETBIOS_NS) += nf_conntrack_netbios_ns.o
 obj-$(CONFIG_NF_CONNTRACK_PPTP) += nf_conntrack_pptp.o
+obj-$(CONFIG_NF_CONNTRACK_SANE) += nf_conntrack_sane.o
 obj-$(CONFIG_NF_CONNTRACK_SIP) += nf_conntrack_sip.o
 obj-$(CONFIG_NF_CONNTRACK_TFTP) += nf_conntrack_tftp.o
 
diff --git a/net/netfilter/nf_conntrack_sane.c b/net/netfilter/nf_conntrack_sane.c
new file mode 100644
index 000000000000..eb2d1dc46d45
--- /dev/null
+++ b/net/netfilter/nf_conntrack_sane.c
@@ -0,0 +1,242 @@
+/* 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>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/netfilter.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>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
+MODULE_DESCRIPTION("SANE connection tracking helper");
+
+static char *sane_buffer;
+
+static DEFINE_SPINLOCK(nf_sane_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);
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+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 **pskb,
+                unsigned int protoff,
+                struct nf_conn *ct,
+                enum ip_conntrack_info ctinfo)
+{
+        unsigned int dataoff, datalen;
+        struct tcphdr _tcph, *th;
+        char *sb_ptr;
+        int ret = NF_ACCEPT;
+        int dir = CTINFO2DIR(ctinfo);
+        struct nf_ct_sane_master *ct_sane_info;
+        struct nf_conntrack_expect *exp;
+        struct nf_conntrack_tuple *tuple;
+        struct sane_request *req;
+        struct sane_reply_net_start *reply;
+        int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
+
+        ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
+        /* Until there's been traffic both ways, don't look in packets. */
+        if (ctinfo != IP_CT_ESTABLISHED &&
+            ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY)
+                return NF_ACCEPT;
+
+        /* Not a full tcp header? */
+        th = skb_header_pointer(*pskb, protoff, sizeof(_tcph), &_tcph);
+        if (th == NULL)
+                return NF_ACCEPT;
+
+        /* No data? */
+        dataoff = protoff + th->doff * 4;
+        if (dataoff >= (*pskb)->len)
+                return NF_ACCEPT;
+
+        datalen = (*pskb)->len - dataoff;
+
+        spin_lock_bh(&nf_sane_lock);
+        sb_ptr = skb_header_pointer(*pskb, dataoff, datalen, sane_buffer);
+        BUG_ON(sb_ptr == NULL);
+
+        if (dir == IP_CT_DIR_ORIGINAL) {
+                if (datalen != sizeof(struct sane_request))
+                        goto out;
+
+                req = (struct sane_request *)sb_ptr;
+                if (req->RPC_code != htonl(SANE_NET_START)) {
+                        /* Not an interesting command */
+                        ct_sane_info->state = SANE_STATE_NORMAL;
+                        goto out;
+                }
+
+                /* We're interested in the next reply */
+                ct_sane_info->state = SANE_STATE_START_REQUESTED;
+                goto out;
+        }
+
+        /* Is it a reply to an uninteresting command? */
+        if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
+                goto out;
+
+        /* It's a reply to SANE_NET_START. */
+        ct_sane_info->state = SANE_STATE_NORMAL;
+
+        if (datalen < sizeof(struct sane_reply_net_start)) {
+                DEBUGP("nf_ct_sane: NET_START reply too short\n");
+                goto out;
+        }
+
+        reply = (struct sane_reply_net_start *)sb_ptr;
+        if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
+                /* saned refused the command */
+                DEBUGP("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
+                        ntohl(reply->status));
+                goto out;
+        }
+
+        /* Invalid saned reply? Ignore it. */
+        if (reply->zero != 0)
+                goto out;
+
+        exp = nf_conntrack_expect_alloc(ct);
+        if (exp == NULL) {
+                ret = NF_DROP;
+                goto out;
+        }
+
+        tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
+        nf_conntrack_expect_init(exp, family,
+                                 &tuple->src.u3, &tuple->dst.u3,
+                                 IPPROTO_TCP,
+                                 NULL, &reply->port);
+
+        DEBUGP("nf_ct_sane: expect: ");
+        NF_CT_DUMP_TUPLE(&exp->tuple);
+        NF_CT_DUMP_TUPLE(&exp->mask);
+
+        /* Can't expect this?  Best to drop packet now. */
+        if (nf_conntrack_expect_related(exp) != 0)
+                ret = NF_DROP;
+
+        nf_conntrack_expect_put(exp);
+
+out:
+        spin_unlock_bh(&nf_sane_lock);
+        return ret;
+}
+
+static struct nf_conntrack_helper sane[MAX_PORTS][2];
+static char sane_names[MAX_PORTS][2][sizeof("sane-65535")];
+
+/* don't make this __exit, since it's called from __init ! */
+static void nf_conntrack_sane_fini(void)
+{
+        int i, j;
+
+        for (i = 0; i < ports_c; i++) {
+                for (j = 0; j < 2; j++) {
+                        DEBUGP("nf_ct_sane: unregistering helper for pf: %d "
+                               "port: %d\n",
+                                sane[i][j].tuple.src.l3num, ports[i]);
+                        nf_conntrack_helper_unregister(&sane[i][j]);
+                }
+        }
+
+        kfree(sane_buffer);
+}
+
+static int __init nf_conntrack_sane_init(void)
+{
+        int i, j = -1, ret = 0;
+        char *tmpname;
+
+        sane_buffer = kmalloc(65536, GFP_KERNEL);
+        if (!sane_buffer)
+                return -ENOMEM;
+
+        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++) {
+                sane[i][0].tuple.src.l3num = PF_INET;
+                sane[i][1].tuple.src.l3num = PF_INET6;
+                for (j = 0; j < 2; j++) {
+                        sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
+                        sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
+                        sane[i][j].mask.src.u.tcp.port = 0xFFFF;
+                        sane[i][j].mask.dst.protonum = 0xFF;
+                        sane[i][j].max_expected = 1;
+                        sane[i][j].timeout = 5 * 60;    /* 5 Minutes */
+                        sane[i][j].me = THIS_MODULE;
+                        sane[i][j].help = help;
+                        tmpname = &sane_names[i][j][0];
+                        if (ports[i] == SANE_PORT)
+                                sprintf(tmpname, "sane");
+                        else
+                                sprintf(tmpname, "sane-%d", ports[i]);
+                        sane[i][j].name = tmpname;
+
+                        DEBUGP("nf_ct_sane: registering helper for pf: %d "
+                               "port: %d\n",
+                                sane[i][j].tuple.src.l3num, ports[i]);
+                        ret = nf_conntrack_helper_register(&sane[i][j]);
+                        if (ret) {
+                                printk(KERN_ERR "nf_ct_sane: failed to "
+                                       "register helper for pf: %d port: %d\n",
+                                        sane[i][j].tuple.src.l3num, ports[i]);
+                                nf_conntrack_sane_fini();
+                                return ret;
+                        }
+                }
+        }
+
+        return 0;
+}
+
+module_init(nf_conntrack_sane_init);
+module_exit(nf_conntrack_sane_fini);