139 lines
3.4 KiB
C
139 lines
3.4 KiB
C
// 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 (dhowells@redhat.com)
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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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