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] =
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(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
132success:
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