xref: /linux/fs/cachefiles/key.c (revision 03ab8e6297acd1bc0eedaa050e2a1635c576fd11)
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 
how_many_hex_digits(unsigned int x)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  */
cachefiles_cook_key(struct cachefiles_object * object)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 }
139