// SPDX-License-Identifier: GPL-2.0-or-later
/* Large capacity key type
 *
 * Copyright (C) 2017-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#define pr_fmt(fmt) "big_key: "fmt
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/file.h>
#include <linux/shmem_fs.h>
#include <linux/err.h>
#include <linux/random.h>
#include <keys/user-type.h>
#include <keys/big_key-type.h>
#include <crypto/chacha20poly1305.h>

/*
 * Layout of key payload words.
 */
enum {
        big_key_data,
        big_key_path,
        big_key_path_2nd_part,
        big_key_len,
};

/*
 * If the data is under this limit, there's no point creating a shm file to
 * hold it as the permanently resident metadata for the shmem fs will be at
 * least as large as the data.
 */
#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))

/*
 * big_key defined keys take an arbitrary string as the description and an
 * arbitrary blob of data as the payload
 */
struct key_type key_type_big_key = {
        .name                   = "big_key",
        .preparse               = big_key_preparse,
        .free_preparse          = big_key_free_preparse,
        .instantiate            = generic_key_instantiate,
        .revoke                 = big_key_revoke,
        .destroy                = big_key_destroy,
        .describe               = big_key_describe,
        .read                   = big_key_read,
        .update                 = big_key_update,
};

/*
 * Preparse a big key
 */
int big_key_preparse(struct key_preparsed_payload *prep)
{
        struct path *path = (struct path *)&prep->payload.data[big_key_path];
        struct file *file;
        u8 *buf, *enckey;
        ssize_t written;
        size_t datalen = prep->datalen;
        size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
        int ret;

        if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
                return -EINVAL;

        /* Set an arbitrary quota */
        prep->quotalen = 16;

        prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;

        if (datalen > BIG_KEY_FILE_THRESHOLD) {
                /* Create a shmem file to store the data in.  This will permit the data
                 * to be swapped out if needed.
                 *
                 * File content is stored encrypted with randomly generated key.
                 * Since the key is random for each file, we can set the nonce
                 * to zero, provided we never define a ->update() call.
                 */
                loff_t pos = 0;

                buf = kvmalloc(enclen, GFP_KERNEL);
                if (!buf)
                        return -ENOMEM;

                /* generate random key */
                enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
                if (!enckey) {
                        ret = -ENOMEM;
                        goto error;
                }
                ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
                if (unlikely(ret))
                        goto err_enckey;

                /* encrypt data */
                chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
                                         0, enckey);

                /* save aligned data to file */
                file = shmem_kernel_file_setup("", enclen, 0);
                if (IS_ERR(file)) {
                        ret = PTR_ERR(file);
                        goto err_enckey;
                }

                written = kernel_write(file, buf, enclen, &pos);
                if (written != enclen) {
                        ret = written;
                        if (written >= 0)
                                ret = -EIO;
                        goto err_fput;
                }

                /* Pin the mount and dentry to the key so that we can open it again
                 * later
                 */
                prep->payload.data[big_key_data] = enckey;
                *path = file->f_path;
                path_get(path);
                fput(file);
                kvfree_sensitive(buf, enclen);
        } else {
                /* Just store the data in a buffer */
                void *data = kmalloc(datalen, GFP_KERNEL);

                if (!data)
                        return -ENOMEM;

                prep->payload.data[big_key_data] = data;
                memcpy(data, prep->data, prep->datalen);
        }
        return 0;

err_fput:
        fput(file);
err_enckey:
        kfree_sensitive(enckey);
error:
        kvfree_sensitive(buf, enclen);
        return ret;
}

/*
 * Clear preparsement.
 */
void big_key_free_preparse(struct key_preparsed_payload *prep)
{
        if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
                struct path *path = (struct path *)&prep->payload.data[big_key_path];

                path_put(path);
        }
        kfree_sensitive(prep->payload.data[big_key_data]);
}

/*
 * dispose of the links from a revoked keyring
 * - called with the key sem write-locked
 */
void big_key_revoke(struct key *key)
{
        struct path *path = (struct path *)&key->payload.data[big_key_path];

        /* clear the quota */
        key_payload_reserve(key, 0);
        if (key_is_positive(key) &&
            (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
                vfs_truncate(path, 0);
}

/*
 * dispose of the data dangling from the corpse of a big_key key
 */
void big_key_destroy(struct key *key)
{
        size_t datalen = (size_t)key->payload.data[big_key_len];

        if (datalen > BIG_KEY_FILE_THRESHOLD) {
                struct path *path = (struct path *)&key->payload.data[big_key_path];

                path_put(path);
                path->mnt = NULL;
                path->dentry = NULL;
        }
        kfree_sensitive(key->payload.data[big_key_data]);
        key->payload.data[big_key_data] = NULL;
}

/*
 * Update a big key
 */
int big_key_update(struct key *key, struct key_preparsed_payload *prep)
{
        int ret;

        ret = key_payload_reserve(key, prep->datalen);
        if (ret < 0)
                return ret;

        if (key_is_positive(key))
                big_key_destroy(key);

        return generic_key_instantiate(key, prep);
}

/*
 * describe the big_key key
 */
void big_key_describe(const struct key *key, struct seq_file *m)
{
        size_t datalen = (size_t)key->payload.data[big_key_len];

        seq_puts(m, key->description);

        if (key_is_positive(key))
                seq_printf(m, ": %zu [%s]",
                           datalen,
                           datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
}

/*
 * read the key data
 * - the key's semaphore is read-locked
 */
long big_key_read(const struct key *key, char *buffer, size_t buflen)
{
        size_t datalen = (size_t)key->payload.data[big_key_len];
        long ret;

        if (!buffer || buflen < datalen)
                return datalen;

        if (datalen > BIG_KEY_FILE_THRESHOLD) {
                struct path *path = (struct path *)&key->payload.data[big_key_path];
                struct file *file;
                u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
                size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
                loff_t pos = 0;

                buf = kvmalloc(enclen, GFP_KERNEL);
                if (!buf)
                        return -ENOMEM;

                file = dentry_open(path, O_RDONLY, current_cred());
                if (IS_ERR(file)) {
                        ret = PTR_ERR(file);
                        goto error;
                }

                /* read file to kernel and decrypt */
                ret = kernel_read(file, buf, enclen, &pos);
                if (ret != enclen) {
                        if (ret >= 0)
                                ret = -EIO;
                        goto err_fput;
                }

                ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
                                               enckey) ? 0 : -EBADMSG;
                if (unlikely(ret))
                        goto err_fput;

                ret = datalen;

                /* copy out decrypted data */
                memcpy(buffer, buf, datalen);

err_fput:
                fput(file);
error:
                kvfree_sensitive(buf, enclen);
        } else {
                ret = datalen;
                memcpy(buffer, key->payload.data[big_key_data], datalen);
        }

        return ret;
}

/*
 * Register key type
 */
static int __init big_key_init(void)
{
        return register_key_type(&key_type_big_key);
}

late_initcall(big_key_init);