/*
 * linux/fs/ext4/crypto_fname.c
 *
 * Copyright (C) 2015, Google, Inc.
 *
 * This contains functions for filename crypto management in ext4
 *
 * Written by Uday Savagaonkar, 2014.
 *
 * This has not yet undergone a rigorous security audit.
 *
 */

#include <crypto/skcipher.h>
#include <keys/encrypted-type.h>
#include <keys/user-type.h>
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/key.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/random.h>
#include <linux/scatterlist.h>
#include <linux/spinlock_types.h>

#include "ext4.h"
#include "ext4_crypto.h"
#include "xattr.h"

/**
 * ext4_dir_crypt_complete() -
 */
static void ext4_dir_crypt_complete(struct crypto_async_request *req, int res)
{
        struct ext4_completion_result *ecr = req->data;

        if (res == -EINPROGRESS)
                return;
        ecr->res = res;
        complete(&ecr->completion);
}

bool ext4_valid_filenames_enc_mode(uint32_t mode)
{
        return (mode == EXT4_ENCRYPTION_MODE_AES_256_CTS);
}

static unsigned max_name_len(struct inode *inode)
{
        return S_ISLNK(inode->i_mode) ? inode->i_sb->s_blocksize :
                EXT4_NAME_LEN;
}

/**
 * ext4_fname_encrypt() -
 *
 * This function encrypts the input filename, and returns the length of the
 * ciphertext. Errors are returned as negative numbers.  We trust the caller to
 * allocate sufficient memory to oname string.
 */
static int ext4_fname_encrypt(struct inode *inode,
                              const struct qstr *iname,
                              struct ext4_str *oname)
{
        u32 ciphertext_len;
        struct skcipher_request *req = NULL;
        DECLARE_EXT4_COMPLETION_RESULT(ecr);
        struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;
        char iv[EXT4_CRYPTO_BLOCK_SIZE];
        struct scatterlist src_sg, dst_sg;
        int padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
        char *workbuf, buf[32], *alloc_buf = NULL;
        unsigned lim = max_name_len(inode);

        if (iname->len <= 0 || iname->len > lim)
                return -EIO;

        ciphertext_len = (iname->len < EXT4_CRYPTO_BLOCK_SIZE) ?
                EXT4_CRYPTO_BLOCK_SIZE : iname->len;
        ciphertext_len = ext4_fname_crypto_round_up(ciphertext_len, padding);
        ciphertext_len = (ciphertext_len > lim)
                        ? lim : ciphertext_len;

        if (ciphertext_len <= sizeof(buf)) {
                workbuf = buf;
        } else {
                alloc_buf = kmalloc(ciphertext_len, GFP_NOFS);
                if (!alloc_buf)
                        return -ENOMEM;
                workbuf = alloc_buf;
        }

        /* Allocate request */
        req = skcipher_request_alloc(tfm, GFP_NOFS);
        if (!req) {
                printk_ratelimited(
                    KERN_ERR "%s: crypto_request_alloc() failed\n", __func__);
                kfree(alloc_buf);
                return -ENOMEM;
        }
        skcipher_request_set_callback(req,
                CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                ext4_dir_crypt_complete, &ecr);

        /* Copy the input */
        memcpy(workbuf, iname->name, iname->len);
        if (iname->len < ciphertext_len)
                memset(workbuf + iname->len, 0, ciphertext_len - iname->len);

        /* Initialize IV */
        memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);

        /* Create encryption request */
        sg_init_one(&src_sg, workbuf, ciphertext_len);
        sg_init_one(&dst_sg, oname->name, ciphertext_len);
        skcipher_request_set_crypt(req, &src_sg, &dst_sg, ciphertext_len, iv);
        res = crypto_skcipher_encrypt(req);
        if (res == -EINPROGRESS || res == -EBUSY) {
                wait_for_completion(&ecr.completion);
                res = ecr.res;
        }
        kfree(alloc_buf);
        skcipher_request_free(req);
        if (res < 0) {
                printk_ratelimited(
                    KERN_ERR "%s: Error (error code %d)\n", __func__, res);
        }
        oname->len = ciphertext_len;
        return res;
}

/*
 * ext4_fname_decrypt()
 *      This function decrypts the input filename, and returns
 *      the length of the plaintext.
 *      Errors are returned as negative numbers.
 *      We trust the caller to allocate sufficient memory to oname string.
 */
static int ext4_fname_decrypt(struct inode *inode,
                              const struct ext4_str *iname,
                              struct ext4_str *oname)
{
        struct ext4_str tmp_in[2], tmp_out[1];
        struct skcipher_request *req = NULL;
        DECLARE_EXT4_COMPLETION_RESULT(ecr);
        struct scatterlist src_sg, dst_sg;
        struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;
        char iv[EXT4_CRYPTO_BLOCK_SIZE];
        unsigned lim = max_name_len(inode);

        if (iname->len <= 0 || iname->len > lim)
                return -EIO;

        tmp_in[0].name = iname->name;
        tmp_in[0].len = iname->len;
        tmp_out[0].name = oname->name;

        /* Allocate request */
        req = skcipher_request_alloc(tfm, GFP_NOFS);
        if (!req) {
                printk_ratelimited(
                    KERN_ERR "%s: crypto_request_alloc() failed\n",  __func__);
                return -ENOMEM;
        }
        skcipher_request_set_callback(req,
                CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                ext4_dir_crypt_complete, &ecr);

        /* Initialize IV */
        memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);

        /* Create encryption request */
        sg_init_one(&src_sg, iname->name, iname->len);
        sg_init_one(&dst_sg, oname->name, oname->len);
        skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
        res = crypto_skcipher_decrypt(req);
        if (res == -EINPROGRESS || res == -EBUSY) {
                wait_for_completion(&ecr.completion);
                res = ecr.res;
        }
        skcipher_request_free(req);
        if (res < 0) {
                printk_ratelimited(
                    KERN_ERR "%s: Error in ext4_fname_encrypt (error code %d)\n",
                    __func__, res);
                return res;
        }

        oname->len = strnlen(oname->name, iname->len);
        return oname->len;
}

static const char *lookup_table =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";

/**
 * ext4_fname_encode_digest() -
 *
 * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 * The encoded string is roughly 4/3 times the size of the input string.
 */
static int digest_encode(const char *src, int len, char *dst)
{
        int i = 0, bits = 0, ac = 0;
        char *cp = dst;

        while (i < len) {
                ac += (((unsigned char) src[i]) << bits);
                bits += 8;
                do {
                        *cp++ = lookup_table[ac & 0x3f];
                        ac >>= 6;
                        bits -= 6;
                } while (bits >= 6);
                i++;
        }
        if (bits)
                *cp++ = lookup_table[ac & 0x3f];
        return cp - dst;
}

static int digest_decode(const char *src, int len, char *dst)
{
        int i = 0, bits = 0, ac = 0;
        const char *p;
        char *cp = dst;

        while (i < len) {
                p = strchr(lookup_table, src[i]);
                if (p == NULL || src[i] == 0)
                        return -2;
                ac += (p - lookup_table) << bits;
                bits += 6;
                if (bits >= 8) {
                        *cp++ = ac & 0xff;
                        ac >>= 8;
                        bits -= 8;
                }
                i++;
        }
        if (ac)
                return -1;
        return cp - dst;
}

/**
 * ext4_fname_crypto_round_up() -
 *
 * Return: The next multiple of block size
 */
u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
{
        return ((size+blksize-1)/blksize)*blksize;
}

unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen)
{
        struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
        int padding = 32;

        if (ci)
                padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
        if (ilen < EXT4_CRYPTO_BLOCK_SIZE)
                ilen = EXT4_CRYPTO_BLOCK_SIZE;
        return ext4_fname_crypto_round_up(ilen, padding);
}

/*
 * ext4_fname_crypto_alloc_buffer() -
 *
 * Allocates an output buffer that is sufficient for the crypto operation
 * specified by the context and the direction.
 */
int ext4_fname_crypto_alloc_buffer(struct inode *inode,
                                   u32 ilen, struct ext4_str *crypto_str)
{
        unsigned int olen = ext4_fname_encrypted_size(inode, ilen);

        crypto_str->len = olen;
        if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
                olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
        /* Allocated buffer can hold one more character to null-terminate the
         * string */
        crypto_str->name = kmalloc(olen+1, GFP_NOFS);
        if (!(crypto_str->name))
                return -ENOMEM;
        return 0;
}

/**
 * ext4_fname_crypto_free_buffer() -
 *
 * Frees the buffer allocated for crypto operation.
 */
void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str)
{
        if (!crypto_str)
                return;
        kfree(crypto_str->name);
        crypto_str->name = NULL;
}

/**
 * ext4_fname_disk_to_usr() - converts a filename from disk space to user space
 */
int _ext4_fname_disk_to_usr(struct inode *inode,
                            struct dx_hash_info *hinfo,
                            const struct ext4_str *iname,
                            struct ext4_str *oname)
{
        char buf[24];
        int ret;

        if (iname->len < 3) {
                /*Check for . and .. */
                if (iname->name[0] == '.' && iname->name[iname->len-1] == '.') {
                        oname->name[0] = '.';
                        oname->name[iname->len-1] = '.';
                        oname->len = iname->len;
                        return oname->len;
                }
        }
        if (iname->len < EXT4_CRYPTO_BLOCK_SIZE) {
                EXT4_ERROR_INODE(inode, "encrypted inode too small");
                return -EUCLEAN;
        }
        if (EXT4_I(inode)->i_crypt_info)
                return ext4_fname_decrypt(inode, iname, oname);

        if (iname->len <= EXT4_FNAME_CRYPTO_DIGEST_SIZE) {
                ret = digest_encode(iname->name, iname->len, oname->name);
                oname->len = ret;
                return ret;
        }
        if (hinfo) {
                memcpy(buf, &hinfo->hash, 4);
                memcpy(buf+4, &hinfo->minor_hash, 4);
        } else
                memset(buf, 0, 8);
        memcpy(buf + 8, iname->name + iname->len - 16, 16);
        oname->name[0] = '_';
        ret = digest_encode(buf, 24, oname->name+1);
        oname->len = ret + 1;
        return ret + 1;
}

int ext4_fname_disk_to_usr(struct inode *inode,
                           struct dx_hash_info *hinfo,
                           const struct ext4_dir_entry_2 *de,
                           struct ext4_str *oname)
{
        struct ext4_str iname = {.name = (unsigned char *) de->name,
                                 .len = de->name_len };

        return _ext4_fname_disk_to_usr(inode, hinfo, &iname, oname);
}


/**
 * ext4_fname_usr_to_disk() - converts a filename from user space to disk space
 */
int ext4_fname_usr_to_disk(struct inode *inode,
                           const struct qstr *iname,
                           struct ext4_str *oname)
{
        int res;
        struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;

        if (iname->len < 3) {
                /*Check for . and .. */
                if (iname->name[0] == '.' &&
                                iname->name[iname->len-1] == '.') {
                        oname->name[0] = '.';
                        oname->name[iname->len-1] = '.';
                        oname->len = iname->len;
                        return oname->len;
                }
        }
        if (ci) {
                res = ext4_fname_encrypt(inode, iname, oname);
                return res;
        }
        /* Without a proper key, a user is not allowed to modify the filenames
         * in a directory. Consequently, a user space name cannot be mapped to
         * a disk-space name */
        return -EACCES;
}

int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
                              int lookup, struct ext4_filename *fname)
{
        struct ext4_crypt_info *ci;
        int ret = 0, bigname = 0;

        memset(fname, 0, sizeof(struct ext4_filename));
        fname->usr_fname = iname;

        if (!ext4_encrypted_inode(dir) ||
            ((iname->name[0] == '.') &&
             ((iname->len == 1) ||
              ((iname->name[1] == '.') && (iname->len == 2))))) {
                fname->disk_name.name = (unsigned char *) iname->name;
                fname->disk_name.len = iname->len;
                return 0;
        }
        ret = ext4_get_encryption_info(dir);
        if (ret)
                return ret;
        ci = EXT4_I(dir)->i_crypt_info;
        if (ci) {
                ret = ext4_fname_crypto_alloc_buffer(dir, iname->len,
                                                     &fname->crypto_buf);
                if (ret < 0)
                        return ret;
                ret = ext4_fname_encrypt(dir, iname, &fname->crypto_buf);
                if (ret < 0)
                        goto errout;
                fname->disk_name.name = fname->crypto_buf.name;
                fname->disk_name.len = fname->crypto_buf.len;
                return 0;
        }
        if (!lookup)
                return -EACCES;

        /* We don't have the key and we are doing a lookup; decode the
         * user-supplied name
         */
        if (iname->name[0] == '_')
                bigname = 1;
        if ((bigname && (iname->len != 33)) ||
            (!bigname && (iname->len > 43)))
                return -ENOENT;

        fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
        if (fname->crypto_buf.name == NULL)
                return -ENOMEM;
        ret = digest_decode(iname->name + bigname, iname->len - bigname,
                            fname->crypto_buf.name);
        if (ret < 0) {
                ret = -ENOENT;
                goto errout;
        }
        fname->crypto_buf.len = ret;
        if (bigname) {
                memcpy(&fname->hinfo.hash, fname->crypto_buf.name, 4);
                memcpy(&fname->hinfo.minor_hash, fname->crypto_buf.name + 4, 4);
        } else {
                fname->disk_name.name = fname->crypto_buf.name;
                fname->disk_name.len = fname->crypto_buf.len;
        }
        return 0;
errout:
        kfree(fname->crypto_buf.name);
        fname->crypto_buf.name = NULL;
        return ret;
}

void ext4_fname_free_filename(struct ext4_filename *fname)
{
        kfree(fname->crypto_buf.name);
        fname->crypto_buf.name = NULL;
        fname->usr_fname = NULL;
        fname->disk_name.name = NULL;
}