/*
  *  C implementation of the Aho-Corasick pattern matching algorithm. It's based

  *  on the ScannerDaemon's version (coded in Java) by Kurt Huwig and

  *  http://www-sr.informatik.uni-tuebingen.de/~buehler/AC/AC.html
  *  Thanks to Kurt Huwig for pointing me to this page.
  *

  *  Copyright (C) 2002 - 2005 Tomasz Kojm <tkojm@clamav.net>

  *
  *  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.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
 #if HAVE_CONFIG_H
 #include "clamav-config.h"
 #endif
 
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include "clamav.h"
 #include "others.h"

 #include "matcher.h"

 #include "matcher-ac.h"
 #include "defaults.h"
 #include "filetypes.h"
 
 #define AC_MIN_LENGTH 2
 
 struct nodelist {
     struct cli_ac_node *node;
     struct nodelist *next;
 };
 
 int cli_ac_addpatt(struct cl_node *root, struct cli_ac_patt *pattern)
 {
 	struct cli_ac_node *pos, *next;
 	int i;
 
     if(pattern->length < AC_MIN_LENGTH)
 	return CL_EPATSHORT;
 
     pos = root->ac_root;
 
     for(i = 0; i < AC_MIN_LENGTH; i++) {
 	next = pos->trans[((unsigned char) pattern->pattern[i]) & 0xff]; 
 
 	if(!next) {
 	    next = (struct cli_ac_node *) cli_calloc(1, sizeof(struct cli_ac_node));
 	    if(!next) {
 		cli_dbgmsg("Unable to allocate pattern node (%d)\n", sizeof(struct cl_node));
 		return CL_EMEM;
 	    }
 
 	    root->ac_nodes++;
 	    root->ac_nodetable = (struct cli_ac_node **) cli_realloc(root->ac_nodetable, (root->ac_nodes) * sizeof(struct cli_ac_node *));
 	    if(root->ac_nodetable == NULL) {
 		cli_dbgmsg("Unable to realloc nodetable (%d)\n", (root->ac_nodes) * sizeof(struct cl_node *));
 		return CL_EMEM;
 	    }
 	    root->ac_nodetable[root->ac_nodes - 1] = next;
 
 	    pos->trans[((unsigned char) pattern->pattern[i]) & 0xff] = next;
 	}
 
 	pos = next;
     }
 
     pos->islast = 1;
 
     pattern->next = pos->list;
     pos->list = pattern;
 
     return 0;
 }
 
 static int cli_enqueue(struct nodelist **bfs, struct cli_ac_node *n)
 {
 	struct nodelist *new;
 
     new = (struct nodelist *) cli_calloc(1, sizeof(struct nodelist));
     if (new == NULL) {
 	cli_dbgmsg("Unable to allocate node list (%d)\n", sizeof(struct nodelist));
 	return CL_EMEM;
     }
 
     new->next = *bfs;
     new->node = n;
     *bfs = new;
     return 0;
 }
 
 static struct cli_ac_node *cli_dequeue(struct nodelist **bfs)
 {
 	struct nodelist *handler, *prev = NULL;
 	struct cli_ac_node *pt;
 
     handler = *bfs;
 
     while(handler && handler->next) {
 	prev = handler;
 	handler = handler->next;
     }
 
     if(!handler) {
 	return NULL;
     } else {
 	pt = handler->node;
 	free(handler);
 	if(prev)
 	    prev->next = NULL;
 	else
 	    *bfs = NULL;
 
 	return pt;
     }
 }
 
 static int cli_maketrans(struct cl_node *root)
 {
 	struct nodelist *bfs = NULL;
 	struct cli_ac_node *ac_root = root->ac_root, *child, *node;
 	int i, ret;
 
 
     ac_root->fail = NULL;
     if((ret = cli_enqueue(&bfs, ac_root)) != 0) {
 	return ret;
     }
 
     while((node = cli_dequeue(&bfs))) {
 	if(node->islast)
 	    continue;
 
 	for(i = 0; i < 256; i++) {
 	    child = node->trans[i];
 	    if(!child) {
 		if(node->fail)
 		    node->trans[i] = (node->fail)->trans[i];
 		else
 		    node->trans[i] = ac_root;
 	    } else {
 		if(node->fail)
 		    child->fail = (node->fail)->trans[i];
 		else
 		    child->fail = ac_root;
 
 		if((ret = cli_enqueue(&bfs, child)) != 0) {
 		    return ret;
 		}
 	    }
 	}
     }
     return 0;
 }
 
 int cli_ac_buildtrie(struct cl_node *root)
 {
 	int ret;
 
     if(!root)
 	return CL_EMALFDB;
 
     if(!root->ac_root) {
 	cli_dbgmsg("Pattern matcher not initialised\n");
 	return 0;
     }
 
     if((ret = cli_addtypesigs(root)))
 	return ret;
 
     return cli_maketrans(root);
 }
 
 static void cli_freepatt(struct cli_ac_patt *list)
 {
 	struct cli_ac_patt *handler, *prev;
 	int i;
 
 
     handler = list;
 
     while(handler) {
 	free(handler->pattern);
 	free(handler->virname);

 	if(handler->offset && (!handler->sigid || handler->partno == 1))

 	    free(handler->offset);

 	if(handler->alt) {
 	    free(handler->altn);
 	    for(i = 0; i < handler->alt; i++)
 		free(handler->altc[i]);
 	    free(handler->altc);
 	}
 	prev = handler;
 	handler = handler->next;
 	free(prev);
     }
 }
 
 void cli_ac_free(struct cl_node *root)
 {
 	unsigned int i;
 
 
     for(i = 0; i < root->ac_nodes; i++) {
 	cli_freepatt(root->ac_nodetable[i]->list);
 	free(root->ac_nodetable[i]);
     }
 
     if(root->ac_nodetable)
 	free(root->ac_nodetable);
 
     if(root->ac_root)
 	free(root->ac_root);
 }
 

 inline static int cli_findpos(const char *buffer, int offset, int length, const struct cli_ac_patt *pattern)

 {
 	int bufferpos = offset + AC_MIN_LENGTH;
 	int postfixend = offset + length;
 	unsigned int i, j, alt = 0, found = 0;
 
 
     if(bufferpos >= length)
 	bufferpos %= length;
 
     for(i = AC_MIN_LENGTH; i < pattern->length; i++) {
 
 	if(bufferpos == postfixend)
 	    return 0;
 
 	if(pattern->pattern[i] == CLI_ALT) {
 	    for(j = 0; j < pattern->altn[alt]; j++) {
 		if(pattern->altc[alt][j] == buffer[bufferpos])
 		    found = 1;
 	    }
 
 	    if(!found)
 		return 0;
 	    alt++;
 
 	} else if(pattern->pattern[i] != CLI_IGN && (char) pattern->pattern[i] != buffer[bufferpos])
 	    return 0;
 
 	bufferpos++;
 
 	if(bufferpos == length)
 	    bufferpos = 0;
     }
 
     return 1;
 }
 

 int cli_ac_scanbuff(const char *buffer, unsigned int length, const char **virname, const struct cl_node *root, int *partcnt, short otfrec, unsigned long int offset, unsigned long int *partoff, unsigned short ftype, int fd)

 {
 	struct cli_ac_node *current;
 	struct cli_ac_patt *pt;

 	int position, type = CL_CLEAN, dist, t;

         unsigned int i;
 
 

     if(!root->ac_root)

 	return CL_CLEAN;
 
     if(!partcnt || !partoff) {
 	cli_dbgmsg("cli_ac_scanbuff(): partcnt == NULL || partoff == NULL\n");
 	return CL_ENULLARG;
     }
 
     current = root->ac_root;
 
     for(i = 0; i < length; i++)  {
 	current = current->trans[(unsigned char) buffer[i] & 0xff];
 
 	if(current->islast) {
 	    position = i - AC_MIN_LENGTH + 1;
 
 	    pt = current->list;
 	    while(pt) {
 		if(cli_findpos(buffer, position, length, pt)) {

 		    if((pt->offset || pt->target) && (!pt->sigid || pt->partno == 1)) {
 			if(ftype == CL_TYPE_UNKNOWN_TEXT)
 			    t = type;
 			else
 			    t = ftype;

 
 			if((fd == -1 && !t) || !cli_validatesig(pt->target, t, pt->offset, offset + position, fd, pt->virname)) {

 			    pt = pt->next;
 			    continue;
 			}
 		    }
 

 		    if(pt->sigid) { /* it's a partial signature */
 			if(partcnt[pt->sigid] + 1 == pt->partno) {
 			    dist = 1;
 			    if(pt->maxdist)
 				if(offset + i - partoff[pt->sigid] > pt->maxdist)
 				    dist = 0;
 
 			    if(dist && pt->mindist)
 				if(offset + i - partoff[pt->sigid] < pt->mindist)
 				    dist = 0;
 
 			    if(dist) {
 				partoff[pt->sigid] = offset + i + pt->length;
 
 				if(++partcnt[pt->sigid] == pt->parts) { /* the last one */
 				    if(pt->type) {

 					if(otfrec) {

 					    if(pt->type > type) {
 						cli_dbgmsg("Matched signature for file type: %s\n", pt->virname);
 						type = pt->type;
 					    }
 					}
 				    } else {
 					if(virname)
 					    *virname = pt->virname;
 
 					return CL_VIRUS;
 				    }
 				}
 			    }
 			}
 
 		    } else { /* old type signature */
 			if(pt->type) {

 			    if(otfrec) {

 				if(pt->type > type) {
 				    cli_dbgmsg("Matched signature for file type: %s\n", pt->virname);
 
 				    type = pt->type;
 				}
 			    }
 			} else {
 			    if(virname)
 				*virname = pt->virname;
 
 			    return CL_VIRUS;
 			}
 		    }
 		}
 
 		pt = pt->next;
 	    }
 
 	    current = current->fail;
 	}
     }
 

     return otfrec ? type : CL_CLEAN;

 }