blob: 81b8b2b3a67476e238650701561474d7c90ed04a [file] [log] [blame]
David Howells9ae326a2009-04-03 16:42:41 +01001/* 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
15static const char cachefiles_charmap[64] =
16 "0123456789" /* 0 - 9 */
17 "abcdefghijklmnopqrstuvwxyz" /* 10 - 35 */
18 "ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* 36 - 61 */
19 "_-" /* 62 - 63 */
20 ;
21
22static 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 */
37char *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}