// 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] __nonstring =
        "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;
        _leave(" = %s", object->d_name);
        return true;
}