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 | |
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 | static 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 | */ |
37 | bool 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(size: 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(size: 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(size: 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 | |
132 | success: |
133 | name[len] = 0; |
134 | object->d_name = name; |
135 | object->d_name_len = len; |
136 | _leave(" = %s" , object->d_name); |
137 | return true; |
138 | } |
139 | |