path: root/source3/smbd/mangle_hash2.c

/* 
   Unix SMB/CIFS implementation.
   new hash based name mangling implementation
   Copyright (C) Andrew Tridgell 2002
   
   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.
*/

/*
  this mangling scheme uses the following format

  Annnn~n.AAA

  where nnnnn is a base 36 hash, and A represents characters from the original string

  The hash is taken of the leading part of the long filename, in uppercase

  for simplicity, we only allow ascii characters in 8.3 names
 */


/*
  ===============================================================================
  NOTE NOTE NOTE!!!

  This file deliberately uses non-multibyte string functions in many places. This
  is *not* a mistake. This code is multi-byte safe, but it gets this property
  through some very subtle knowledge of the way multi-byte strings are encoded 
  and the fact that this mangling algorithm only supports ascii characters in
  8.3 names.

  please don't convert this file to use the *_m() functions!!
  ===============================================================================
*/


#include "includes.h"


#define FLAG_BASECHAR 1
#define FLAG_ASCII 2
#define FLAG_ILLEGAL 4
#define FLAG_POSSIBLE1 8
#define FLAG_POSSIBLE2 16
#define FLAG_POSSIBLE3 32

#define CACHE_SIZE 8192

/* these tables are used to provide fast tests for characters */
static unsigned char char_flags[256];

/* we will use a very simple direct mapped prefix cache. The big
   advantage of this cache structure is speed and low memory usage 

   The cache is indexed by the low-order bits of the hash, and confirmed by
   hashing the resulting cache entry to match the known hash
*/
static char **prefix_cache;

/* these are the characters we use in the 8.3 hash. Must be 36 chars long */
const char *basechars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
static unsigned char base_reverse[256];
#define base_forward(v) basechars[v]

/* the list of reserved dos names - all of these are illegal */
const char *reserved_names[] = { "AUX", "LOCK$", "CON", "COM1", "COM2", "COM3", "COM4",
				 "LPT1", "LPT2", "LPT3", "NUL", "PRN", NULL };

/* 
   hash a string of the specified length. The string does not need to be
   null terminated 

   this hash needs to be fast with a low collision rate (what hash doesn't?)
*/
static u32 mangle_hash(const char *key, unsigned length)
{
	u32 value;
	u32   i;
	fstring str;

	strncpy(str, key, length);
	str[length] = 0;
	strupper_m(str);

	/* the length of a multi-byte string can change after a strupper */
	length = strlen(str);

	/* Set the initial value from the key size. */
	for (value = 0x238F13AF * length, i=0; i < length; i++) {
		value = (value + (((unsigned char)str[i]) << (i*5 % 24)));
	}

	return (1103515243 * value + 12345);  
}

/* 
   initialise the prefix cache
 */
static BOOL cache_init(void)
{
	if (prefix_cache) return True;

	prefix_cache = malloc(sizeof(char *) * CACHE_SIZE);
	if (!prefix_cache) return False;

	memset(prefix_cache, 0, sizeof(char *) * CACHE_SIZE);
	return True;
}

/*
  insert an entry into the prefix cache. The string may not be null terminated
*/
static void cache_insert(const char *prefix, int length, u32 hash)
{
	int i = hash % CACHE_SIZE;

	if (prefix_cache[i]) {
		free(prefix_cache[i]);
	}

	prefix_cache[i] = strndup(prefix, length);
}

/*
  lookup an entry in the prefix cache. Return NULL if not found.
*/
static const char *cache_lookup(u32 hash)
{
	int i = hash % CACHE_SIZE;

	if (!prefix_cache[i]) return NULL;

	/* we have a possible match - compute the hash to confirm */
	if (hash != mangle_hash(prefix_cache[i], strlen(prefix_cache[i]))) {
		return NULL;
	}

	/* yep, it matched */
	return prefix_cache[i];
}


/* 
   determine if a string is possibly in a mangled format, ignoring
   case 

   In this algorithm, mangled names use only pure ascii characters (no
   multi-byte) so we can avoid doing a UCS2 conversion 
*/
static BOOL is_mangled(const char *name)
{
	/* the best distinguishing characteristic is the ~ */
	if (name[6] != '~') return False;

	/* check extension */
	/* check first character */
	/* check rest of hash */

	return True;
}


/* 
   see if a filename is an allowable 8.3 name.

   we are only going to allow ascii characters in 8.3 names, as this
   simplifies things greatly (it means that we know the string won't
   get larger when converted from UNIX to DOS formats)
*/
static BOOL is_8_3(const char *name, BOOL check_case)
{
	int len, i;
	char *dot_p;

	/* as a special case, the names '.' and '..' are allowable 8.3 names */
	if (name[0] == '.') {
		if (!name[1] || (name[1] == '.' && !name[2])) {
			return True;
		}
	}

	/* the simplest test is on the overall length of the
	 filename. Note that we deliberately use the ascii string
	 length (not the multi-byte one) as it is faster, and gives us
	 the result we need in this case. Using strlen_m would not
	 only be slower, it would be incorrect */
	len = strlen(name);
	if (len > 12) return False;

	/* find the '.'. Note that once again we use the non-multibyte
           function */
	dot_p = strchr(name, '.');

	if (!dot_p) {
		/* if the name doesn't contain a '.' then its length
                   must be less than 8 */
		if (len > 8) {
			return False;
		}
	} else {
		int prefix_len, suffix_len;

		/* if it does contain a dot then the prefix must be <=
		   8 and the suffix <= 3 in length */
		prefix_len = PTR_DIFF(dot_p, name);
		suffix_len = len - (prefix_len+1);

		if (prefix_len > 8 || suffix_len > 3) {
			return False;
		}

		/* a 8.3 name cannot contain more than 1 '.' */
		if (strchr(dot_p+1, '.')) {
			return False;
		}
	}

	/* the length are all OK. Now check to see if the characters themselves are OK */
	for (i=0; name[i]; i++) {
		if (!(char_flags[(unsigned)(name[i])] & FLAG_ASCII)) {
			return False;
		}
	}

	/* it is a good 8.3 name */
	return True;
}


/*
  reset the mangling cache on a smb.conf reload. This only really makes sense for
  mangling backends that have parameters in smb.conf, and as this backend doesn't
  this is a NULL operation
*/
static void mangle_reset(void)
{
	/* noop */
}


/*
  try to find a 8.3 name in the cache, and if found then
  replace the string with the original long name. 

  The filename must be able to hold at least sizeof(fstring) 
*/
static BOOL check_cache(char *name)
{
	u32 hash, multiplier;
	int i;
	const char *prefix;
	char extension[4];

	/* make sure that this is a mangled name from this cache */
	if (!is_mangled(name)) {
		return False;
	}

	/* we need to extract the hash from the 8.3 name */
	hash = base_reverse[(unsigned char)name[7]];
	for (multiplier=36, i=5;i>=1;i--) {
		u32 v = base_reverse[(unsigned char)name[i]];
		hash += multiplier * v;
		multiplier *= 36;
	}

	/* now look in the prefix cache for that hash */
	prefix = cache_lookup(hash);
	if (!prefix) {
		return False;
	}

	/* we found it - construct the full name */
	strncpy(extension, name+9, 3);

	if (extension[0]) {
		slprintf(name, sizeof(fstring), "%s.%s", prefix, extension);
	} else {
		fstrcpy(name, prefix);
	}
	return True;
}


/*
  look for a DOS reserved name
*/
static BOOL is_reserved_name(const char *name)
{
	if ((char_flags[(unsigned char)name[0]] & FLAG_POSSIBLE1) &&
	    (char_flags[(unsigned char)name[1]] & FLAG_POSSIBLE2) &&
	    (char_flags[(unsigned char)name[2]] & FLAG_POSSIBLE3)) {
		/* a likely match, scan the lot */
		int i;
		for (i=0; reserved_names[i]; i++) {
			int len = strlen(reserved_names[i]);
			/* note that we match on COM1 as well as COM1.foo */
			if (strncasecmp(name, reserved_names[i], len) == 0 &&
			    (name[len] == '.' || name[len] == 0)) {
				return True;
			}
		}
	}

	return False;
}

/*
  see if a filename is a legal long filename
*/
static BOOL is_legal_name(const char *name)
{
	while (*name) {
		if (char_flags[(unsigned char)*name] & FLAG_ILLEGAL) {
			return False;
		}
		name++;
	}

	return True;
}

/*
  the main forward mapping function, which converts a long filename to 
  a 8.3 name

  if need83 is not set then we only do the mangling if the name is illegal
  as a long name

  if cache83 is not set then we don't cache the result

  the name parameter must be able to hold 13 bytes
*/
static BOOL name_map(char *name, BOOL need83, BOOL cache83)
{
	char *dot_p;
	char lead_char;
	char extension[4];
	int extension_length, i;
	int prefix_len;
	u32 hash, v;
	char new_name[13];

	/* reserved names are handled specially */
	if (!is_reserved_name(name)) {
		/* if the name is already a valid 8.3 name then we don't need to 
		   do anything */
		if (is_8_3(name, False)) {
			return True;
		}

		/* if the caller doesn't strictly need 8.3 then just check for illegal 
		   filenames */
		if (!need83 && is_legal_name(name)) {
			return True;
		}
	}

	/* find the '.' if any */
	dot_p = strchr(name, '.');

	/* the leading character in the mangled name is taken from
	   the first character of the name, if it is ascii 
	   otherwise '_' is used
	*/
	lead_char = name[0];
	if (! (char_flags[(unsigned char)lead_char] & FLAG_ASCII)) {
		lead_char = '_';
	}

	/* the prefix is anything up to the first dot */
	if (dot_p) {
		prefix_len = PTR_DIFF(dot_p, name);
	} else {
		prefix_len = strlen(name);
	}

	/* the extension of the mangled name is taken from the first 3
	   ascii chars after the dot */
	extension_length = 0;
	if (dot_p) {
		for (i=1; extension_length < 3 && dot_p[i]; i++) {
			char c = dot_p[i];
			if (char_flags[(unsigned char)c] & FLAG_ASCII) {
				extension[extension_length++] = c;
			}
		}
	}
	   
	/* find the hash for this prefix */
	v = hash = mangle_hash(name, prefix_len);

	/* now form the mangled name */
	new_name[0] = lead_char;
	new_name[7] = base_forward(v % 36);
	new_name[6] = '~';	
	for (i=5; i>=1; i--) {
		v = v / 36;
		new_name[i] = base_forward(v % 36);
	}

	/* add the extension */
	if (extension_length) {
		new_name[8] = '.';
		memcpy(&new_name[9], extension, extension_length);
		new_name[9+extension_length] = 0;
	} else {
		new_name[8] = 0;
	}

	if (cache83) {
		/* put it in the cache */
		cache_insert(name, prefix_len, hash);
	}

	/* and overwrite the old name */
	fstrcpy(name, new_name);

	/* all done, we've managed to mangle it */
	return True;
}


/* initialise the flags table 

  we allow only a very restricted set of characters as 'ascii' in this
  mangling backend. This isn't a significant problem as modern clients
  use the 'long' filenames anyway, and those don't have these
  restrictions. 
*/
static void init_tables(void)
{
	int i;

	memset(char_flags, 0, sizeof(char_flags));

	for (i=0;i<128;i++) {
		if ((i >= '0' && i <= '9') || 
		    (i >= 'a' && i <= 'z') || 
		    (i >= 'A' && i <= 'Z')) {
			char_flags[i] |=  (FLAG_ASCII | FLAG_BASECHAR);
		}
		if (strchr("._-$~", i)) {
			char_flags[i] |= FLAG_ASCII;
		}

		if (strchr("*\\/?<>|\":", i)) {
			char_flags[i] |= FLAG_ILLEGAL;
		}
	}

	memset(base_reverse, 0, sizeof(base_reverse));
	for (i=0;i<36;i++) {
		base_reverse[(unsigned char)base_forward(i)] = i;
	}	

	/* fill in the reserved names flags. These are used as a very
	   fast filter for finding possible DOS reserved filenames */
	for (i=0; reserved_names[i]; i++) {
		unsigned char c1, c2, c3;

		c1 = (unsigned char)reserved_names[i][0];
		c2 = (unsigned char)reserved_names[i][1];
		c3 = (unsigned char)reserved_names[i][2];

		char_flags[c1] |= FLAG_POSSIBLE1;
		char_flags[c2] |= FLAG_POSSIBLE2;
		char_flags[c3] |= FLAG_POSSIBLE3;
		char_flags[tolower(c1)] |= FLAG_POSSIBLE1;
		char_flags[tolower(c2)] |= FLAG_POSSIBLE2;
		char_flags[tolower(c3)] |= FLAG_POSSIBLE3;
	}
}


/*
  the following provides the abstraction layer to make it easier
  to drop in an alternative mangling implementation */
static struct mangle_fns mangle_fns = {
	is_mangled,
	is_8_3,
	mangle_reset,
	check_cache,
	name_map
};

/* return the methods for this mangling implementation */
struct mangle_fns *mangle_hash2_init(void)
{
	init_tables();
	mangle_reset();

	if (!cache_init()) {
		return NULL;
	}

	return &mangle_fns;
}