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1// SPDX-License-Identifier: GPL-2.0-or-later2/* Key to pathname encoder3 *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 cooked32 * - 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 of34 * cooked35 * - 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-bit68 * chunk. We rely on the key having been padded out to a whole number69 * 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 else97 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