/* 
  Kernel module to match application layer (OSI layer 7) 
  data in connections.
  
  http://l7-filter.sf.net

  By Matthew Strait and Ethan Sommer, 2003-2005.

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation; either version
  2 of the License, or (at your option) any later version.
  http://www.gnu.org/licenses/gpl.txt

  Based on ipt_string.c (C) 2000 Emmanuel Roger <winfield@freegates.be>
  and cls_layer7.c (C) 2003 Matthew Strait, Ethan Sommer, Justin Levandoski
*/

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/proc_fs.h>
#include <linux/ctype.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4/lockhelp.h>

#include "regexp/regexp.c"

#include <linux/netfilter_ipv4/ipt_layer7.h>
#include <linux/netfilter_ipv4/ip_tables.h>

MODULE_AUTHOR("Matthew Strait <quadong@users.sf.net>, Ethan Sommer <sommere@users.sf.net>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("iptables application layer match module");

static int maxdatalen = 2048; // this is the default
MODULE_PARM(maxdatalen,"i");
MODULE_PARM_DESC(maxdatalen,"maximum bytes of data looked at by l7-filter");

#if defined(CONFIG_IP_NF_MATCH_LAYER7_DEBUG)
	#define DPRINTK(format,args...) printk(format,##args)
#else
	#define DPRINTK(format,args...)
#endif

#define TOTAL_PACKETS master_conntrack->layer7.numpackets

/* Number of packets whose data we look at.
This can be modified through /proc/net/layer7_numpackets */
static int num_packets = 10;

static struct pattern_cache {
	char * regex_string;
	regexp * pattern;
	struct pattern_cache * next;
} * first_pattern_cache = NULL;

/* I'm new to locking.  Here are my assumptions:

- No one will write to /proc/net/layer7_numpackets over and over very fast; 
  if they did, nothing awful would happen.

- This code will never be processing the same packet twice at the same time,
  because iptables rules are traversed in order.

- It doesn't matter if two packets from different connections are in here at 
  the same time, because they don't share any data.

- It _does_ matter if two packets from the same connection are here at the same
  time.  In this case, we have to protect the conntracks and the list of 
  compiled patterns.
*/
DECLARE_RWLOCK(ct_lock);
DECLARE_LOCK(list_lock);

#if CONFIG_IP_NF_MATCH_LAYER7_DEBUG
/* Converts an unfriendly string into a friendly one by 
replacing unprintables with periods and all whitespace with " ". */
static char * friendly_print(unsigned char * s)
{
	char * f = kmalloc(strlen(s) + 1, GFP_ATOMIC);
	int i;

	if(!f) {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: out of memory in friendly_print, bailing.\n");
		return NULL;
	}

	for(i = 0; i < strlen(s); i++){
		if(isprint(s[i]) && s[i] < 128)	f[i] = s[i];
		else if(isspace(s[i]))		f[i] = ' ';
		else 				f[i] = '.';
	}
	f[i] = '\0';
	return f;
}

static char dec2hex(int i)
{
	switch (i) {
		case 0 ... 9:
			return (char)(i + '0');
			break;
		case 10 ... 15:
			return (char)(i - 10 + 'a');
			break;
		default:
			if (net_ratelimit()) 
				printk("Problem in dec2hex\n");
			return '\0';
	}
}

static char * hex_print(unsigned char * s)
{
	char * g = kmalloc(strlen(s)*3 + 1, GFP_ATOMIC);
	int i;

	if(!g) {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: out of memory in hex_print, bailing.\n");
		return NULL;
	}

	for(i = 0; i < strlen(s); i++) {
		g[i*3    ] = dec2hex(s[i]/16);
		g[i*3 + 1] = dec2hex(s[i]%16);
		g[i*3 + 2] = ' ';
	}
	g[i*3] = '\0';

	return g;
}
#endif // DEBUG

/* Use instead of regcomp.  As we expect to be seeing the same regexps over and
over again, it make sense to cache the results. */
static regexp * compile_and_cache(char * regex_string, char * protocol) 
{
	struct pattern_cache * node               = first_pattern_cache;
	struct pattern_cache * last_pattern_cache = first_pattern_cache;
	struct pattern_cache * tmp;
	unsigned int len;

	while (node != NULL) {
		if (!strcmp(node->regex_string, regex_string)) 
			return node->pattern;

		last_pattern_cache = node;/* points at the last non-NULL node */
		node = node->next;
	}

	/* If we reach the end of the list, then we have not yet cached
	   the pattern for this regex. Let's do that now. 
	   Be paranoid about running out of memory to avoid list corruption. */
	tmp = kmalloc(sizeof(struct pattern_cache), GFP_ATOMIC);

	if(!tmp) {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: out of memory in compile_and_cache, bailing.\n");
		return NULL;
	}

	tmp->regex_string  = kmalloc(strlen(regex_string) + 1, GFP_ATOMIC);
	tmp->pattern       = kmalloc(sizeof(struct regexp),    GFP_ATOMIC);
	tmp->next = NULL;

	if(!tmp->regex_string || !tmp->pattern) {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: out of memory in compile_and_cache, bailing.\n");
		kfree(tmp->regex_string);
		kfree(tmp->pattern);
		kfree(tmp);
		return NULL;
	}

	/* Ok.  The new node is all ready now. */
	node = tmp;

	if(first_pattern_cache == NULL) /* list is empty */
		first_pattern_cache = node; /* make node the beginning */
	else
		last_pattern_cache->next = node; /* attach node to the end */

	/* copy the string and compile the regex */
	len = strlen(regex_string);
	DPRINTK("About to compile this: \"%s\"\n", regex_string);
	node->pattern = regcomp(regex_string, &len);
	if ( !node->pattern ) {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: Error compiling regexp \"%s\" (%s)\n", regex_string, protocol);
		/* pattern is now cached as NULL, so we won't try again. */
	}

	strcpy(node->regex_string, regex_string);
	return node->pattern;
}

static int can_handle(const struct sk_buff *skb)
{
	if(!skb->nh.iph) /* not IP */
		return 0;
	if(skb->nh.iph->protocol != IPPROTO_TCP &&
	   skb->nh.iph->protocol != IPPROTO_UDP &&
	   skb->nh.iph->protocol != IPPROTO_ICMP)
		return 0;
	return 1;
}

/* Returns offset the into the skb->data that the application data starts */
static int app_data_offset(const struct sk_buff *skb)
{
	/* In case we are ported somewhere (ebtables?) where skb->nh.iph 
	isn't set, this can be gotten from 4*(skb->data[0] & 0x0f) as well. */
	int ip_hl = 4*skb->nh.iph->ihl;

	if( skb->nh.iph->protocol == IPPROTO_TCP ) {
		/* 12 == offset into TCP header for the header length field. 
		Can't get this with skb->h.th->doff because the tcphdr 
		struct doesn't get set when routing (this is confirmed to be 
		true in Netfilter as well as QoS.) */
		int tcp_hl = 4*(skb->data[ip_hl + 12] >> 4);

		return ip_hl + tcp_hl;
	} else if( skb->nh.iph->protocol == IPPROTO_UDP  ) {
		return ip_hl + 8; /* UDP header is always 8 bytes */
	} else if( skb->nh.iph->protocol == IPPROTO_ICMP ) {
		return ip_hl + 8; /* ICMP header is 8 bytes */
	} else {
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: tried to handle unknown protocol!\n");
		return ip_hl + 8; /* something reasonable */
	}
}

/* handles whether there's a match when we aren't appending data anymore */
static int match_no_append(struct ip_conntrack * conntrack, struct ip_conntrack * master_conntrack,
			enum ip_conntrack_info ctinfo, enum ip_conntrack_info master_ctinfo,
			struct ipt_layer7_info * info)
{
	/* If we're in here, throw the app data away */
	WRITE_LOCK(&ct_lock);
	if(master_conntrack->layer7.app_data != NULL) {

	#ifdef CONFIG_IP_NF_MATCH_LAYER7_DEBUG
		if(!master_conntrack->layer7.app_proto) {
			char * f = friendly_print(master_conntrack->layer7.app_data);
			char * g = hex_print(master_conntrack->layer7.app_data);
			DPRINTK("\nl7-filter gave up after %d bytes (%d packets):\n%s\n",
				strlen(f), 
				TOTAL_PACKETS, f);
			kfree(f); 
			DPRINTK("In hex: %s\n", g);
			kfree(g);
		}
	#endif

		kfree(master_conntrack->layer7.app_data);
		master_conntrack->layer7.app_data = NULL; /* don't free again */
	}
	WRITE_UNLOCK(&ct_lock);

	if(master_conntrack->layer7.app_proto){
		/* Here child connections set their .app_proto (for /proc/net/ip_conntrack) */
		WRITE_LOCK(&ct_lock);
		if(!conntrack->layer7.app_proto) {
			conntrack->layer7.app_proto = kmalloc(strlen(master_conntrack->layer7.app_proto)+1, GFP_ATOMIC);
			if(!conntrack->layer7.app_proto){
				if (net_ratelimit()) 
					printk(KERN_ERR "layer7: out of memory in match_no_append, bailing.\n");
				WRITE_UNLOCK(&ct_lock);
				return 1;
			}
			strcpy(conntrack->layer7.app_proto, master_conntrack->layer7.app_proto);
		}
		WRITE_UNLOCK(&ct_lock);
	
		return (!strcmp(master_conntrack->layer7.app_proto, info->protocol));
	}
	else {
		/* If not classified, set to "unknown" to distinguish from 
		connections that are still being tested. */
		WRITE_LOCK(&ct_lock);
		master_conntrack->layer7.app_proto = kmalloc(strlen("unknown")+1, GFP_ATOMIC);
		if(!master_conntrack->layer7.app_proto){
			if (net_ratelimit()) 
				printk(KERN_ERR "layer7: out of memory in match_no_append, bailing.\n");
			WRITE_UNLOCK(&ct_lock);
			return 1;
		}
		strcpy(master_conntrack->layer7.app_proto, "unknown");
		WRITE_UNLOCK(&ct_lock);
		return 0;
	}
}

/* add the new app data to the conntrack.  Return number of bytes added. */
static int add_data(struct ip_conntrack * master_conntrack, 
			char * app_data, int appdatalen)
{
	int length = 0, i;
	int oldlength = master_conntrack->layer7.app_data_len;

	/* Strip nulls. Make everything lower case (our regex lib doesn't
	do case insensitivity).  Add it to the end of the current data. */
	for(i = 0; i < maxdatalen-oldlength-1 && i < appdatalen; i++) {
		if(app_data[i] != '\0') {
			master_conntrack->layer7.app_data[length+oldlength] = 
				/* the kernel version of tolower mungs 'upper ascii' */
				isascii(app_data[i])? tolower(app_data[i]) : app_data[i];
			length++;
		}
	}

	master_conntrack->layer7.app_data[length+oldlength] = '\0';
	master_conntrack->layer7.app_data_len = length + oldlength;

	return length;
}

/* Returns true on match and false otherwise.  */
static int match(/* const */struct sk_buff *skb, const struct net_device *in,
		 const struct net_device *out, const void *matchinfo,
		 int offset,		   int *hotdrop)
{
	struct ipt_layer7_info * info = (struct ipt_layer7_info *)matchinfo;
	enum ip_conntrack_info master_ctinfo, ctinfo;
	struct ip_conntrack *master_conntrack, *conntrack;
	unsigned char * app_data;  
	unsigned int pattern_result, appdatalen;
	regexp * comppattern;

	if(!can_handle(skb)){
		DPRINTK("layer7: This is some protocol I can't handle.\n");
		return info->invert;
	}

	/* Treat the parent and all its children together as one connection, 
	except for the purpose of setting conntrack->layer7.app_proto in the 
	actual connection. This makes /proc/net/ip_conntrack somewhat more 
	satisfying. */
	if(!(conntrack	= ip_conntrack_get((struct sk_buff *)skb, &ctinfo)) ||
	   !(master_conntrack = ip_conntrack_get((struct sk_buff *)skb, &master_ctinfo))) {
		DPRINTK("layer7: packet is not from a known connection, giving up.\n");
		return info->invert;
	}
	
	/* Try to get a master conntrack (and its master etc) for FTP, etc. */
	while (master_ct(master_conntrack) != NULL)
		master_conntrack = master_ct(master_conntrack);

	if(!skb->cb[0]){
		WRITE_LOCK(&ct_lock);
		master_conntrack->layer7.numpackets++;/*starts at 0 via memset*/
		WRITE_UNLOCK(&ct_lock);
	}

	/* if we've classified it or seen too many packets */
	if(TOTAL_PACKETS > num_packets || 
	   master_conntrack->layer7.app_proto) {
	
		pattern_result = match_no_append(conntrack, master_conntrack, ctinfo, master_ctinfo, info);
	
		/* skb->cb[0] == seen. Avoid doing things twice if there are two l7 
		rules. I'm not sure that using cb for this purpose is correct, although
		it says "put your private variables there". But it doesn't look like it
		is being used for anything else in the skbs that make it here. How can
		I write to cb without making the compiler angry? */
		skb->cb[0] = 1; /* marking it seen here is probably irrelevant, but consistant */

		return (pattern_result ^ info->invert);
	}

	if(skb_is_nonlinear(skb)){
		if(skb_linearize(skb, GFP_ATOMIC) != 0){
			if (net_ratelimit()) 
				printk(KERN_ERR "layer7: failed to linearize packet, bailing.\n");
			return info->invert;
		}
	}
	
	/* now that the skb is linearized, it's safe to set these. */
	app_data = skb->data + app_data_offset(skb);
	appdatalen = skb->tail - app_data;

	LOCK_BH(&list_lock);
	/* the return value gets checked later, when we're ready to use it */
	comppattern = compile_and_cache(info->pattern, info->protocol);
	UNLOCK_BH(&list_lock);

	/* On the first packet of a connection, allocate space for app data */
	WRITE_LOCK(&ct_lock);
	if(TOTAL_PACKETS == 1 && !skb->cb[0] && !master_conntrack->layer7.app_data) {
		master_conntrack->layer7.app_data = kmalloc(maxdatalen, GFP_ATOMIC);
		if(!master_conntrack->layer7.app_data){
			if (net_ratelimit())
				printk(KERN_ERR "layer7: out of memory in match, bailing.\n");
			WRITE_UNLOCK(&ct_lock);
			return info->invert;
		}

		master_conntrack->layer7.app_data[0] = '\0';
	}
	WRITE_UNLOCK(&ct_lock);

	/* Can be here, but unallocated, if numpackets is increased near 
	the beginning of a connection */
	if(master_conntrack->layer7.app_data == NULL)
		return (info->invert); /* unmatched */

	if(!skb->cb[0]){
		int newbytes;
		WRITE_LOCK(&ct_lock);
		newbytes = add_data(master_conntrack, app_data, appdatalen);
		WRITE_UNLOCK(&ct_lock);

		if(newbytes == 0) { /* didn't add any data */
			skb->cb[0] = 1;
			/* Didn't match before, not going to match now */
			return info->invert;
		}
	}

	/* If looking for "unknown", then never match.  "Unknown" means that
	we've given up; we're still trying with these packets. */
	if(!strcmp(info->protocol, "unknown")) {
		pattern_result = 0;
	/* If the regexp failed to compile, don't bother running it */
	} else if(comppattern && regexec(comppattern, master_conntrack->layer7.app_data)) {
		DPRINTK("layer7: regexec positive: %s!\n", info->protocol);
		pattern_result = 1;
	} else pattern_result = 0;

	if(pattern_result) {
		WRITE_LOCK(&ct_lock);
		master_conntrack->layer7.app_proto = kmalloc(strlen(info->protocol)+1, GFP_ATOMIC);
		if(!master_conntrack->layer7.app_proto){
			if (net_ratelimit()) 
				printk(KERN_ERR "layer7: out of memory in match, bailing.\n");
			WRITE_UNLOCK(&ct_lock);
			return (pattern_result ^ info->invert);
		}
		strcpy(master_conntrack->layer7.app_proto, info->protocol);
		WRITE_UNLOCK(&ct_lock);
	}

	/* mark the packet seen */
	skb->cb[0] = 1;

	return (pattern_result ^ info->invert);
}

static int checkentry(const char *tablename, const struct ipt_ip *ip,
	   void *matchinfo, unsigned int matchsize, unsigned int hook_mask)
{
	if (matchsize != IPT_ALIGN(sizeof(struct ipt_layer7_info))) 
		return 0;
	return 1;
}

static struct ipt_match layer7_match = { 
	.name = "layer7", 
	.match = &match, 
	.checkentry = &checkentry, 
	.me = THIS_MODULE 
};

/* taken from drivers/video/modedb.c */
static int my_atoi(const char *s)
{
	int val = 0;

	for (;; s++) {
		switch (*s) {
		case '0'...'9':
			val = 10*val+(*s-'0');
			break;
		default:
			return val;
		}
	}
}

/* write out num_packets to userland. */
static int layer7_read_proc(char* page, char ** start, off_t off, int count, 
		     int* eof, void * data) 
{
	if(num_packets > 99 && net_ratelimit()) 
		printk(KERN_ERR "layer7: NOT REACHED. num_packets too big\n");
	
	page[0] = num_packets/10 + '0';
	page[1] = num_packets%10 + '0';
	page[2] = '\n';
	page[3] = '\0';
		
	*eof=1;

	return 3;
}

/* Read in num_packets from userland */
static int layer7_write_proc(struct file* file, const char* buffer, 
		      unsigned long count, void *data) 
{
	char * foo = kmalloc(count, GFP_ATOMIC);

	if(!foo){
		if (net_ratelimit()) 
			printk(KERN_ERR "layer7: out of memory, bailing. num_packets unchanged.\n");
		return count;
	}

	copy_from_user(foo, buffer, count);

	num_packets = my_atoi(foo);
	kfree (foo);

	/* This has an arbitrary limit to make the math easier. I'm lazy. 
	But anyway, 99 is a LOT! If you want more, you're doing it wrong! */
	if(num_packets > 99) {
		printk(KERN_WARNING "layer7: num_packets can't be > 99.\n");
		num_packets = 99;
	} else if(num_packets < 1) {
		printk(KERN_WARNING "layer7: num_packets can't be < 1.\n");
		num_packets = 1;
	}
	
	return count;
}

/* register the proc file */
static void layer7_init_proc(void)
{
	struct proc_dir_entry* entry;
	entry = create_proc_entry("layer7_numpackets", 0644, proc_net);
	entry->read_proc = layer7_read_proc;
	entry->write_proc = layer7_write_proc;
}

static void layer7_cleanup_proc(void)
{
	remove_proc_entry("layer7_numpackets", proc_net);
}

static int __init init(void)
{
	layer7_init_proc();
	if(maxdatalen < 1) {
		printk(KERN_WARNING "layer7: maxdatalen can't be < 1, using 1\n");
		maxdatalen = 1;
	}
	/* This is not a hard limit.  It's just here to prevent people from     
	bringing their slow machines to a grinding halt. */
	else if(maxdatalen > 65536) {
		printk(KERN_WARNING "layer7: maxdatalen can't be > 65536, using 65536\n");
		maxdatalen = 65536;             
	}
	return ipt_register_match(&layer7_match);
}

static void __exit fini(void)
{
	layer7_cleanup_proc();
	ipt_unregister_match(&layer7_match);
}

module_init(init);
module_exit(fini);