/* Large capacity key type
 *
 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/file.h>
#include <linux/shmem_fs.h>
#include <linux/err.h>
#include <keys/user-type.h>
#include <keys/big_key-type.h>

MODULE_LICENSE("GPL");

/*
 * 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,
};

/*
 * Preparse a big key
 */
int big_key_preparse(struct key_preparsed_payload *prep)
{
        struct path *path = (struct path *)&prep->payload;
        struct file *file;
        ssize_t written;
        size_t datalen = prep->datalen;
        int ret;

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

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

        prep->type_data[1] = (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.
                 *
                 * TODO: Encrypt the stored data with a temporary key.
                 */
                file = shmem_kernel_file_setup("", datalen, 0);
                if (IS_ERR(file)) {
                        ret = PTR_ERR(file);
                        goto error;
                }

                written = kernel_write(file, prep->data, prep->datalen, 0);
                if (written != datalen) {
                        ret = written;
                        if (written >= 0)
                                ret = -ENOMEM;
                        goto err_fput;
                }

                /* Pin the mount and dentry to the key so that we can open it again
                 * later
                 */
                *path = file->f_path;
                path_get(path);
                fput(file);
        } else {
                /* Just store the data in a buffer */
                void *data = kmalloc(datalen, GFP_KERNEL);
                if (!data)
                        return -ENOMEM;

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

err_fput:
        fput(file);
error:
        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;
                path_put(path);
        } else {
                kfree(prep->payload[0]);
        }
}

/*
 * 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.data2;

        /* clear the quota */
        key_payload_reserve(key, 0);
        if (key_is_instantiated(key) && key->type_data.x[1] > 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)
{
        if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
                struct path *path = (struct path *)&key->payload.data2;
                path_put(path);
                path->mnt = NULL;
                path->dentry = NULL;
        } else {
                kfree(key->payload.data);
                key->payload.data = NULL;
        }
}

/*
 * describe the big_key key
 */
void big_key_describe(const struct key *key, struct seq_file *m)
{
        unsigned long datalen = key->type_data.x[1];

        seq_puts(m, key->description);

        if (key_is_instantiated(key))
                seq_printf(m, ": %lu [%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 __user *buffer, size_t buflen)
{
        unsigned long datalen = key->type_data.x[1];
        long ret;

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

        if (datalen > BIG_KEY_FILE_THRESHOLD) {
                struct path *path = (struct path *)&key->payload.data2;
                struct file *file;
                loff_t pos;

                file = dentry_open(path, O_RDONLY, current_cred());
                if (IS_ERR(file))
                        return PTR_ERR(file);

                pos = 0;
                ret = vfs_read(file, buffer, datalen, &pos);
                fput(file);
                if (ret >= 0 && ret != datalen)
                        ret = -EIO;
        } else {
                ret = datalen;
                if (copy_to_user(buffer, key->payload.data, datalen) != 0)
                        ret = -EFAULT;
        }

        return ret;
}

/*
 * Module stuff
 */
static int __init big_key_init(void)
{
        return register_key_type(&key_type_big_key);
}

static void __exit big_key_cleanup(void)
{
        unregister_key_type(&key_type_big_key);
}

module_init(big_key_init);
module_exit(big_key_cleanup);