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