1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Key to pathname encoder
3 *
4 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #include <linux/slab.h>
9 #include "internal.h"
10
11 static const char cachefiles_charmap[64] =
12 "0123456789" /* 0 - 9 */
13 "abcdefghijklmnopqrstuvwxyz" /* 10 - 35 */
14 "ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* 36 - 61 */
15 "_-" /* 62 - 63 */
16 ;
17
18 static const char cachefiles_filecharmap[256] = {
19 /* we skip space and tab and control chars */
20 [33 ... 46] = 1, /* '!' -> '.' */
21 /* we skip '/' as it's significant to pathwalk */
22 [48 ... 127] = 1, /* '0' -> '~' */
23 };
24
25 /*
26 * turn the raw key into something cooked
27 * - the raw key should include the length in the two bytes at the front
28 * - the key may be up to 514 bytes in length (including the length word)
29 * - "base64" encode the strange keys, mapping 3 bytes of raw to four of
30 * cooked
31 * - need to cut the cooked key into 252 char lengths (189 raw bytes)
32 */
33 char *cachefiles_cook_key(const u8 *raw, int keylen, uint8_t type)
34 {
35 unsigned char csum, ch;
36 unsigned int acc;
37 char *key;
38 int loop, len, max, seg, mark, print;
39
40 _enter(",%d", keylen);
41
42 BUG_ON(keylen < 2 || keylen > 514);
43
44 csum = raw[0] + raw[1];
45 print = 1;
46 for (loop = 2; loop < keylen; loop++) {
47 ch = raw[loop];
48 csum += ch;
49 print &= cachefiles_filecharmap[ch];
50 }
51
52 if (print) {
53 /* if the path is usable ASCII, then we render it directly */
54 max = keylen - 2;
55 max += 2; /* two base64'd length chars on the front */
56 max += 5; /* @checksum/M */
57 max += 3 * 2; /* maximum number of segment dividers (".../M")
58 * is ((514 + 251) / 252) = 3
59 */
60 max += 1; /* NUL on end */
61 } else {
62 /* calculate the maximum length of the cooked key */
63 keylen = (keylen + 2) / 3;
64
65 max = keylen * 4;
66 max += 5; /* @checksum/M */
67 max += 3 * 2; /* maximum number of segment dividers (".../M")
68 * is ((514 + 188) / 189) = 3
69 */
70 max += 1; /* NUL on end */
71 }
72
73 max += 1; /* 2nd NUL on end */
74
75 _debug("max: %d", max);
76
77 key = kmalloc(max, cachefiles_gfp);
78 if (!key)
79 return NULL;
80
81 len = 0;
82
83 /* build the cooked key */
84 sprintf(key, "@%02x%c+", (unsigned) csum, 0);
85 len = 5;
86 mark = len - 1;
87
88 if (print) {
89 acc = *(uint16_t *) raw;
90 raw += 2;
91
92 key[len + 1] = cachefiles_charmap[acc & 63];
93 acc >>= 6;
94 key[len] = cachefiles_charmap[acc & 63];
95 len += 2;
96
97 seg = 250;
98 for (loop = keylen; loop > 0; loop--) {
99 if (seg <= 0) {
100 key[len++] = '\0';
101 mark = len;
102 key[len++] = '+';
103 seg = 252;
104 }
105
106 key[len++] = *raw++;
107 ASSERT(len < max);
108 }
109
110 switch (type) {
111 case FSCACHE_COOKIE_TYPE_INDEX: type = 'I'; break;
112 case FSCACHE_COOKIE_TYPE_DATAFILE: type = 'D'; break;
113 default: type = 'S'; break;
114 }
115 } else {
116 seg = 252;
117 for (loop = keylen; loop > 0; loop--) {
118 if (seg <= 0) {
119 key[len++] = '\0';
120 mark = len;
121 key[len++] = '+';
122 seg = 252;
123 }
124
125 acc = *raw++;
126 acc |= *raw++ << 8;
127 acc |= *raw++ << 16;
128
129 _debug("acc: %06x", acc);
130
131 key[len++] = cachefiles_charmap[acc & 63];
132 acc >>= 6;
133 key[len++] = cachefiles_charmap[acc & 63];
134 acc >>= 6;
135 key[len++] = cachefiles_charmap[acc & 63];
136 acc >>= 6;
137 key[len++] = cachefiles_charmap[acc & 63];
138
139 ASSERT(len < max);
140 }
141
142 switch (type) {
143 case FSCACHE_COOKIE_TYPE_INDEX: type = 'J'; break;
144 case FSCACHE_COOKIE_TYPE_DATAFILE: type = 'E'; break;
145 default: type = 'T'; break;
146 }
147 }
148
149 key[mark] = type;
150 key[len++] = 0;
151 key[len] = 0;
152
153 _leave(" = %p %d", key, len);
154 return key;
155 }