/*
 * This contains functions for filename crypto management
 *
 * Copyright (C) 2015, Google, Inc.
 * Copyright (C) 2015, Motorola Mobility
 *
 * Written by Uday Savagaonkar, 2014.
 * Modified by Jaegeuk Kim, 2015.
 *
 * This has not yet undergone a rigorous security audit.
 */

#include <keys/encrypted-type.h>
#include <keys/user-type.h>
#include <linux/scatterlist.h>
#include <linux/ratelimit.h>
#include <linux/fscrypto.h>

static u32 size_round_up(size_t size, size_t blksize)
{
        return ((size + blksize - 1) / blksize) * blksize;
}

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

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

/**
 * 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 fname_encrypt(struct inode *inode,
                        const struct qstr *iname, struct fscrypt_str *oname)
{
        u32 ciphertext_len;
        struct skcipher_request *req = NULL;
        DECLARE_FS_COMPLETION_RESULT(ecr);
        struct fscrypt_info *ci = inode->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;
        char iv[FS_CRYPTO_BLOCK_SIZE];
        struct scatterlist src_sg, dst_sg;
        int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
        char *workbuf, buf[32], *alloc_buf = NULL;
        unsigned lim;

        lim = inode->i_sb->s_cop->max_namelen(inode);
        if (iname->len <= 0 || iname->len > lim)
                return -EIO;

        ciphertext_len = (iname->len < FS_CRYPTO_BLOCK_SIZE) ?
                                        FS_CRYPTO_BLOCK_SIZE : iname->len;
        ciphertext_len = size_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,
                        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, FS_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;
}

/*
 * 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 fname_decrypt(struct inode *inode,
                                const struct fscrypt_str *iname,
                                struct fscrypt_str *oname)
{
        struct skcipher_request *req = NULL;
        DECLARE_FS_COMPLETION_RESULT(ecr);
        struct scatterlist src_sg, dst_sg;
        struct fscrypt_info *ci = inode->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;
        char iv[FS_CRYPTO_BLOCK_SIZE];
        unsigned lim;

        lim = inode->i_sb->s_cop->max_namelen(inode);
        if (iname->len <= 0 || iname->len > lim)
                return -EIO;

        /* 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,
                dir_crypt_complete, &ecr);

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

        /* Create decryption 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 (error code %d)\n", __func__, res);
                return res;
        }

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

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

/**
 * digest_encode() -
 *
 * 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;
}

u32 fscrypt_fname_encrypted_size(struct inode *inode, u32 ilen)
{
        int padding = 32;
        struct fscrypt_info *ci = inode->i_crypt_info;

        if (ci)
                padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
        if (ilen < FS_CRYPTO_BLOCK_SIZE)
                ilen = FS_CRYPTO_BLOCK_SIZE;
        return size_round_up(ilen, padding);
}
EXPORT_SYMBOL(fscrypt_fname_encrypted_size);

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

        crypto_str->len = olen;
        if (olen < FS_FNAME_CRYPTO_DIGEST_SIZE * 2)
                olen = FS_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;
}
EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);

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

/**
 * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 * space
 */
int fscrypt_fname_disk_to_usr(struct inode *inode,
                        u32 hash, u32 minor_hash,
                        const struct fscrypt_str *iname,
                        struct fscrypt_str *oname)
{
        const struct qstr qname = FSTR_TO_QSTR(iname);
        char buf[24];
        int ret;

        if (fscrypt_is_dot_dotdot(&qname)) {
                oname->name[0] = '.';
                oname->name[iname->len - 1] = '.';
                oname->len = iname->len;
                return oname->len;
        }

        if (iname->len < FS_CRYPTO_BLOCK_SIZE)
                return -EUCLEAN;

        if (inode->i_crypt_info)
                return fname_decrypt(inode, iname, oname);

        if (iname->len <= FS_FNAME_CRYPTO_DIGEST_SIZE) {
                ret = digest_encode(iname->name, iname->len, oname->name);
                oname->len = ret;
                return ret;
        }
        if (hash) {
                memcpy(buf, &hash, 4);
                memcpy(buf + 4, &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;
}
EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);

/**
 * fscrypt_fname_usr_to_disk() - converts a filename from user space to disk
 * space
 */
int fscrypt_fname_usr_to_disk(struct inode *inode,
                        const struct qstr *iname,
                        struct fscrypt_str *oname)
{
        if (fscrypt_is_dot_dotdot(iname)) {
                oname->name[0] = '.';
                oname->name[iname->len - 1] = '.';
                oname->len = iname->len;
                return oname->len;
        }
        if (inode->i_crypt_info)
                return fname_encrypt(inode, iname, oname);
        /*
         * 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;
}
EXPORT_SYMBOL(fscrypt_fname_usr_to_disk);

int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
                              int lookup, struct fscrypt_name *fname)
{
        int ret = 0, bigname = 0;

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

        if (!dir->i_sb->s_cop->is_encrypted(dir) ||
                                fscrypt_is_dot_dotdot(iname)) {
                fname->disk_name.name = (unsigned char *)iname->name;
                fname->disk_name.len = iname->len;
                return 0;
        }
        ret = get_crypt_info(dir);
        if (ret && ret != -EOPNOTSUPP)
                return ret;

        if (dir->i_crypt_info) {
                ret = fscrypt_fname_alloc_buffer(dir, iname->len,
                                                        &fname->crypto_buf);
                if (ret < 0)
                        return ret;
                ret = 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->hash, fname->crypto_buf.name, 4);
                memcpy(&fname->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:
        fscrypt_fname_free_buffer(&fname->crypto_buf);
        return ret;
}
EXPORT_SYMBOL(fscrypt_setup_filename);

void fscrypt_free_filename(struct fscrypt_name *fname)
{
        kfree(fname->crypto_buf.name);
        fname->crypto_buf.name = NULL;
        fname->usr_fname = NULL;
        fname->disk_name.name = NULL;
}
EXPORT_SYMBOL(fscrypt_free_filename);