fs/cachefiles/key.c

   1 /* Key to pathname encoder
   2  *
   3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/slab.h>
  13 #include "internal.h"
  14
  15 static const char cachefiles_charmap[64] =
  16         "0123456789"                    /* 0 - 9 */
  17         "abcdefghijklmnopqrstuvwxyz"    /* 10 - 35 */
  18         "ABCDEFGHIJKLMNOPQRSTUVWXYZ"    /* 36 - 61 */
  19         "_-"                            /* 62 - 63 */
  20         ;
  21
  22 static const char cachefiles_filecharmap[256] = {
  23         /* we skip space and tab and control chars */
  24         [33 ... 46] = 1,                /* '!' -> '.' */
  25         /* we skip '/' as it's significant to pathwalk */
  26         [48 ... 127] = 1,               /* '0' -> '~' */
  27 };
  28
  29 /*
  30  * turn the raw key into something cooked
  31  * - the raw key should include the length in the two bytes at the front
  32  * - the key may be up to 514 bytes in length (including the length word)
  33  *   - "base64" encode the strange keys, mapping 3 bytes of raw to four of
  34  *     cooked
  35  *   - need to cut the cooked key into 252 char lengths (189 raw bytes)
  36  */
  37 char *cachefiles_cook_key(const u8 *raw, int keylen, uint8_t type)
  38 {
  39         unsigned char csum, ch;
  40         unsigned int acc;
  41         char *key;
  42         int loop, len, max, seg, mark, print;
  43
  44         _enter(",%d", keylen);
  45
  46         BUG_ON(keylen < 2 || keylen > 514);
  47
  48         csum = raw[0] + raw[1];
  49         print = 1;
  50         for (loop = 2; loop < keylen; loop++) {
  51                 ch = raw[loop];
  52                 csum += ch;
  53                 print &= cachefiles_filecharmap[ch];
  54         }
  55
  56         if (print) {
  57                 /* if the path is usable ASCII, then we render it directly */
  58                 max = keylen - 2;
  59                 max += 2;       /* two base64'd length chars on the front */
  60                 max += 5;       /* @checksum/M */
  61                 max += 3 * 2;   /* maximum number of segment dividers (".../M")
  62                                  * is ((514 + 251) / 252) = 3
  63                                  */
  64                 max += 1;       /* NUL on end */
  65         } else {
  66                 /* calculate the maximum length of the cooked key */
  67                 keylen = (keylen + 2) / 3;
  68
  69                 max = keylen * 4;
  70                 max += 5;       /* @checksum/M */
  71                 max += 3 * 2;   /* maximum number of segment dividers (".../M")
  72                                  * is ((514 + 188) / 189) = 3
  73                                  */
  74                 max += 1;       /* NUL on end */
  75         }
  76
  77         max += 1;       /* 2nd NUL on end */
  78
  79         _debug("max: %d", max);
  80
  81         key = kmalloc(max, GFP_KERNEL);
  82         if (!key)
  83                 return NULL;
  84
  85         len = 0;
  86
  87         /* build the cooked key */
  88         sprintf(key, "@%02x%c+", (unsigned) csum, 0);
  89         len = 5;
  90         mark = len - 1;
  91
  92         if (print) {
  93                 acc = *(uint16_t *) raw;
  94                 raw += 2;
  95
  96                 key[len + 1] = cachefiles_charmap[acc & 63];
  97                 acc >>= 6;
  98                 key[len] = cachefiles_charmap[acc & 63];
  99                 len += 2;
 100
 101                 seg = 250;
 102                 for (loop = keylen; loop > 0; loop--) {
 103                         if (seg <= 0) {
 104                                 key[len++] = '\0';
 105                                 mark = len;
 106                                 key[len++] = '+';
 107                                 seg = 252;
 108                         }
 109
 110                         key[len++] = *raw++;
 111                         ASSERT(len < max);
 112                 }
 113
 114                 switch (type) {
 115                 case FSCACHE_COOKIE_TYPE_INDEX:         type = 'I';     break;
 116                 case FSCACHE_COOKIE_TYPE_DATAFILE:      type = 'D';     break;
 117                 default:                                type = 'S';     break;
 118                 }
 119         } else {
 120                 seg = 252;
 121                 for (loop = keylen; loop > 0; loop--) {
 122                         if (seg <= 0) {
 123                                 key[len++] = '\0';
 124                                 mark = len;
 125                                 key[len++] = '+';
 126                                 seg = 252;
 127                         }
 128
 129                         acc = *raw++;
 130                         acc |= *raw++ << 8;
 131                         acc |= *raw++ << 16;
 132
 133                         _debug("acc: %06x", acc);
 134
 135                         key[len++] = cachefiles_charmap[acc & 63];
 136                         acc >>= 6;
 137                         key[len++] = cachefiles_charmap[acc & 63];
 138                         acc >>= 6;
 139                         key[len++] = cachefiles_charmap[acc & 63];
 140                         acc >>= 6;
 141                         key[len++] = cachefiles_charmap[acc & 63];
 142
 143                         ASSERT(len < max);
 144                 }
 145
 146                 switch (type) {
 147                 case FSCACHE_COOKIE_TYPE_INDEX:         type = 'J';     break;
 148                 case FSCACHE_COOKIE_TYPE_DATAFILE:      type = 'E';     break;
 149                 default:                                type = 'T';     break;
 150                 }
 151         }
 152
 153         key[mark] = type;
 154         key[len++] = 0;
 155         key[len] = 0;
 156
 157         _leave(" = %p %d", key, len);
 158         return key;
 159 }