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5d439467 DH |
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(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(be); | |
78 | nle += 1 + how_many_hex_digits(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(name + len, nlen - len, "%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 | ||
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 | } |