// SPDX-License-Identifier: GPL-2.0
/*
 * 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 <linux/scatterlist.h>
#include <linux/ratelimit.h>
#include "fscrypt_private.h"

/**
 * fname_encrypt() - encrypt a filename
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * Return: 0 on success, -errno on failure
 */
static int fname_encrypt(struct inode *inode,
                        const struct qstr *iname, struct fscrypt_str *oname)
{
        struct skcipher_request *req = NULL;
        DECLARE_CRYPTO_WAIT(wait);
        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 sg;
        int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
        unsigned int lim;
        unsigned int cryptlen;

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

        /*
         * Copy the filename to the output buffer for encrypting in-place and
         * pad it with the needed number of NUL bytes.
         */
        cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
        cryptlen = round_up(cryptlen, padding);
        cryptlen = min(cryptlen, lim);
        memcpy(oname->name, iname->name, iname->len);
        memset(oname->name + iname->len, 0, cryptlen - iname->len);

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

        /* Set up the encryption request */
        req = skcipher_request_alloc(tfm, GFP_NOFS);
        if (!req) {
                printk_ratelimited(KERN_ERR
                        "%s: skcipher_request_alloc() failed\n", __func__);
                return -ENOMEM;
        }
        skcipher_request_set_callback(req,
                        CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                        crypto_req_done, &wait);
        sg_init_one(&sg, oname->name, cryptlen);
        skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);

        /* Do the encryption */
        res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
        skcipher_request_free(req);
        if (res < 0) {
                printk_ratelimited(KERN_ERR
                                "%s: Error (error code %d)\n", __func__, res);
                return res;
        }

        oname->len = cryptlen;
        return 0;
}

/**
 * fname_decrypt() - decrypt a filename
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * Return: 0 on success, -errno on failure
 */
static int fname_decrypt(struct inode *inode,
                                const struct fscrypt_str *iname,
                                struct fscrypt_str *oname)
{
        struct skcipher_request *req = NULL;
        DECLARE_CRYPTO_WAIT(wait);
        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,
                crypto_req_done, &wait);

        /* 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_wait_req(crypto_skcipher_decrypt(req), &wait);
        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 0;
}

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

#define BASE64_CHARS(nbytes)    DIV_ROUND_UP((nbytes) * 4, 3)

/**
 * 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(const 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);
        ilen = max(ilen, (u32)FS_CRYPTO_BLOCK_SIZE);
        return 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(const struct inode *inode,
                                u32 ilen, struct fscrypt_str *crypto_str)
{
        u32 olen = fscrypt_fname_encrypted_size(inode, ilen);
        const u32 max_encoded_len =
                max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
                      1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));

        crypto_str->len = olen;
        olen = max(olen, max_encoded_len);

        /*
         * 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
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 * it for presentation.  Short names are directly base64-encoded, while long
 * names are encoded in fscrypt_digested_name format.
 *
 * Return: 0 on success, -errno on failure
 */
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);
        struct fscrypt_digested_name digested_name;

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

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

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

        if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
                oname->len = digest_encode(iname->name, iname->len,
                                           oname->name);
                return 0;
        }
        if (hash) {
                digested_name.hash = hash;
                digested_name.minor_hash = minor_hash;
        } else {
                digested_name.hash = 0;
                digested_name.minor_hash = 0;
        }
        memcpy(digested_name.digest,
               FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
               FSCRYPT_FNAME_DIGEST_SIZE);
        oname->name[0] = '_';
        oname->len = 1 + digest_encode((const char *)&digested_name,
                                       sizeof(digested_name), oname->name + 1);
        return 0;
}
EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);

/**
 * fscrypt_fname_usr_to_disk() - converts a filename from user space to disk
 * space
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * Return: 0 on success, -errno on failure
 */
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 0;
        }
        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 -ENOKEY;
}
EXPORT_SYMBOL(fscrypt_fname_usr_to_disk);

/**
 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 * @dir: the directory that will be searched
 * @iname: the user-provided filename being searched for
 * @lookup: 1 if we're allowed to proceed without the key because it's
 *      ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 *      proceed without the key because we're going to create the dir_entry.
 * @fname: the filename information to be filled in
 *
 * Given a user-provided filename @iname, this function sets @fname->disk_name
 * to the name that would be stored in the on-disk directory entry, if possible.
 * If the directory is unencrypted this is simply @iname.  Else, if we have the
 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 * get the disk_name.
 *
 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 * we decode it to get either the ciphertext disk_name (for short names) or the
 * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 * impossible in this case, so we fail them with ENOKEY.
 *
 * If successful, fscrypt_free_filename() must be called later to clean up.
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
                              int lookup, struct fscrypt_name *fname)
{
        int ret;
        int digested;

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

        if (!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 = fscrypt_get_encryption_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)
                        return ret;
                ret = fname_encrypt(dir, iname, &fname->crypto_buf);
                if (ret)
                        goto errout;
                fname->disk_name.name = fname->crypto_buf.name;
                fname->disk_name.len = fname->crypto_buf.len;
                return 0;
        }
        if (!lookup)
                return -ENOKEY;

        /*
         * We don't have the key and we are doing a lookup; decode the
         * user-supplied name
         */
        if (iname->name[0] == '_') {
                if (iname->len !=
                    1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
                        return -ENOENT;
                digested = 1;
        } else {
                if (iname->len >
                    BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
                        return -ENOENT;
                digested = 0;
        }

        fname->crypto_buf.name =
                kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
                              sizeof(struct fscrypt_digested_name)),
                        GFP_KERNEL);
        if (fname->crypto_buf.name == NULL)
                return -ENOMEM;

        ret = digest_decode(iname->name + digested, iname->len - digested,
                                fname->crypto_buf.name);
        if (ret < 0) {
                ret = -ENOENT;
                goto errout;
        }
        fname->crypto_buf.len = ret;
        if (digested) {
                const struct fscrypt_digested_name *n =
                        (const void *)fname->crypto_buf.name;
                fname->hash = n->hash;
                fname->minor_hash = n->minor_hash;
        } 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);