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138 lines
3.4 KiB
138 lines
3.4 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* Key to pathname encoder |
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* |
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* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved. |
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* Written by David Howells ([email protected]) |
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*/ |
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#include <linux/slab.h> |
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#include "internal.h" |
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static const char cachefiles_charmap[64] = |
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"0123456789" /* 0 - 9 */ |
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"abcdefghijklmnopqrstuvwxyz" /* 10 - 35 */ |
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"ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* 36 - 61 */ |
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"_-" /* 62 - 63 */ |
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; |
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static const char cachefiles_filecharmap[256] = { |
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/* we skip space and tab and control chars */ |
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[33 ... 46] = 1, /* '!' -> '.' */ |
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/* we skip '/' as it's significant to pathwalk */ |
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[48 ... 127] = 1, /* '0' -> '~' */ |
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}; |
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static inline unsigned int how_many_hex_digits(unsigned int x) |
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{ |
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return x ? round_up(ilog2(x) + 1, 4) / 4 : 0; |
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} |
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/* |
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* turn the raw key into something cooked |
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* - the key may be up to NAME_MAX in length (including the length word) |
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* - "base64" encode the strange keys, mapping 3 bytes of raw to four of |
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* cooked |
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* - need to cut the cooked key into 252 char lengths (189 raw bytes) |
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*/ |
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bool cachefiles_cook_key(struct cachefiles_object *object) |
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{ |
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const u8 *key = fscache_get_key(object->cookie), *kend; |
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unsigned char ch; |
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unsigned int acc, i, n, nle, nbe, keylen = object->cookie->key_len; |
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unsigned int b64len, len, print, pad; |
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char *name, sep; |
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_enter(",%u,%*phN", keylen, keylen, key); |
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BUG_ON(keylen > NAME_MAX - 3); |
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print = 1; |
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for (i = 0; i < keylen; i++) { |
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ch = key[i]; |
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print &= cachefiles_filecharmap[ch]; |
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} |
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/* If the path is usable ASCII, then we render it directly */ |
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if (print) { |
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len = 1 + keylen; |
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name = kmalloc(len + 1, GFP_KERNEL); |
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if (!name) |
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return false; |
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name[0] = 'D'; /* Data object type, string encoding */ |
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memcpy(name + 1, key, keylen); |
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goto success; |
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} |
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/* See if it makes sense to encode it as "hex,hex,hex" for each 32-bit |
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* chunk. We rely on the key having been padded out to a whole number |
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* of 32-bit words. |
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*/ |
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n = round_up(keylen, 4); |
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nbe = nle = 0; |
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for (i = 0; i < n; i += 4) { |
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u32 be = be32_to_cpu(*(__be32 *)(key + i)); |
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u32 le = le32_to_cpu(*(__le32 *)(key + i)); |
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nbe += 1 + how_many_hex_digits(be); |
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nle += 1 + how_many_hex_digits(le); |
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} |
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b64len = DIV_ROUND_UP(keylen, 3); |
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pad = b64len * 3 - keylen; |
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b64len = 2 + b64len * 4; /* Length if we base64-encode it */ |
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_debug("len=%u nbe=%u nle=%u b64=%u", keylen, nbe, nle, b64len); |
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if (nbe < b64len || nle < b64len) { |
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unsigned int nlen = min(nbe, nle) + 1; |
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name = kmalloc(nlen, GFP_KERNEL); |
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if (!name) |
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return false; |
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sep = (nbe <= nle) ? 'S' : 'T'; /* Encoding indicator */ |
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len = 0; |
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for (i = 0; i < n; i += 4) { |
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u32 x; |
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if (nbe <= nle) |
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x = be32_to_cpu(*(__be32 *)(key + i)); |
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else |
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x = le32_to_cpu(*(__le32 *)(key + i)); |
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name[len++] = sep; |
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if (x != 0) |
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len += snprintf(name + len, nlen - len, "%x", x); |
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sep = ','; |
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} |
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goto success; |
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} |
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/* We need to base64-encode it */ |
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name = kmalloc(b64len + 1, GFP_KERNEL); |
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if (!name) |
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return false; |
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name[0] = 'E'; |
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name[1] = '0' + pad; |
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len = 2; |
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kend = key + keylen; |
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do { |
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acc = *key++; |
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if (key < kend) { |
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acc |= *key++ << 8; |
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if (key < kend) |
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acc |= *key++ << 16; |
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} |
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name[len++] = cachefiles_charmap[acc & 63]; |
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acc >>= 6; |
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name[len++] = cachefiles_charmap[acc & 63]; |
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acc >>= 6; |
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name[len++] = cachefiles_charmap[acc & 63]; |
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acc >>= 6; |
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name[len++] = cachefiles_charmap[acc & 63]; |
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} while (key < kend); |
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success: |
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name[len] = 0; |
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object->d_name = name; |
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object->d_name_len = len; |
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_leave(" = %s", object->d_name); |
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return true; |
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}
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