1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Key to pathname encoder
3 *
4 * Copyright (C) 2021 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
11static const char cachefiles_charmap[64] __nonstring =
12 "0123456789" /* 0 - 9 */
13 "abcdefghijklmnopqrstuvwxyz" /* 10 - 35 */
14 "ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* 36 - 61 */
15 "_-" /* 62 - 63 */
16 ;
17
18static 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
25static inline unsigned int how_many_hex_digits(unsigned int x)
26{
27 return x ? round_up(ilog2(x) + 1, 4) / 4 : 0;
28}
29
30/*
31 * turn the raw key into something cooked
32 * - the key may be up to NAME_MAX 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 */
37bool cachefiles_cook_key(struct cachefiles_object *object)
38{
39 const u8 *key = fscache_get_key(cookie: object->cookie), *kend;
40 unsigned char ch;
41 unsigned int acc, i, n, nle, nbe, keylen = object->cookie->key_len;
42 unsigned int b64len, len, print, pad;
43 char *name, sep;
44
45 _enter(",%u,%*phN", keylen, keylen, key);
46
47 BUG_ON(keylen > NAME_MAX - 3);
48
49 print = 1;
50 for (i = 0; i < keylen; i++) {
51 ch = key[i];
52 print &= cachefiles_filecharmap[ch];
53 }
54
55 /* If the path is usable ASCII, then we render it directly */
56 if (print) {
57 len = 1 + keylen;
58 name = kmalloc(len + 1, GFP_KERNEL);
59 if (!name)
60 return false;
61
62 name[0] = 'D'; /* Data object type, string encoding */
63 memcpy(name + 1, key, keylen);
64 goto success;
65 }
66
67 /* See if it makes sense to encode it as "hex,hex,hex" for each 32-bit
68 * chunk. We rely on the key having been padded out to a whole number
69 * of 32-bit words.
70 */
71 n = round_up(keylen, 4);
72 nbe = nle = 0;
73 for (i = 0; i < n; i += 4) {
74 u32 be = be32_to_cpu(*(__be32 *)(key + i));
75 u32 le = le32_to_cpu(*(__le32 *)(key + i));
76
77 nbe += 1 + how_many_hex_digits(x: be);
78 nle += 1 + how_many_hex_digits(x: le);
79 }
80
81 b64len = DIV_ROUND_UP(keylen, 3);
82 pad = b64len * 3 - keylen;
83 b64len = 2 + b64len * 4; /* Length if we base64-encode it */
84 _debug("len=%u nbe=%u nle=%u b64=%u", keylen, nbe, nle, b64len);
85 if (nbe < b64len || nle < b64len) {
86 unsigned int nlen = min(nbe, nle) + 1;
87 name = kmalloc(nlen, GFP_KERNEL);
88 if (!name)
89 return false;
90 sep = (nbe <= nle) ? 'S' : 'T'; /* Encoding indicator */
91 len = 0;
92 for (i = 0; i < n; i += 4) {
93 u32 x;
94 if (nbe <= nle)
95 x = be32_to_cpu(*(__be32 *)(key + i));
96 else
97 x = le32_to_cpu(*(__le32 *)(key + i));
98 name[len++] = sep;
99 if (x != 0)
100 len += snprintf(buf: name + len, size: nlen - len, fmt: "%x", x);
101 sep = ',';
102 }
103 goto success;
104 }
105
106 /* We need to base64-encode it */
107 name = kmalloc(b64len + 1, GFP_KERNEL);
108 if (!name)
109 return false;
110
111 name[0] = 'E';
112 name[1] = '0' + pad;
113 len = 2;
114 kend = key + keylen;
115 do {
116 acc = *key++;
117 if (key < kend) {
118 acc |= *key++ << 8;
119 if (key < kend)
120 acc |= *key++ << 16;
121 }
122
123 name[len++] = cachefiles_charmap[acc & 63];
124 acc >>= 6;
125 name[len++] = cachefiles_charmap[acc & 63];
126 acc >>= 6;
127 name[len++] = cachefiles_charmap[acc & 63];
128 acc >>= 6;
129 name[len++] = cachefiles_charmap[acc & 63];
130 } while (key < kend);
131
132success:
133 name[len] = 0;
134 object->d_name = name;
135 _leave(" = %s", object->d_name);
136 return true;
137}
138

source code of linux/fs/cachefiles/key.c