// SPDX-License-Identifier: GPL-2.0-or-later

  /* Large capacity key type
   *

   * Copyright (C) 2017 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/scatterlist.h>

  #include <linux/random.h>

  #include <linux/vmalloc.h>

  #include <keys/user-type.h>
  #include <keys/big_key-type.h>

  #include <crypto/aead.h>

  #include <crypto/gcm.h>

  struct big_key_buf {
  	unsigned int		nr_pages;
  	void			*virt;
  	struct scatterlist	*sg;
  	struct page		*pages[];
  };

  /*

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

   * Crypto operation with big_key data
   */
  enum big_key_op {
  	BIG_KEY_ENC,
  	BIG_KEY_DEC,
  };
  
  /*

   * 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))
  
  /*

   * Key size for big_key data encryption
   */

  #define ENC_KEY_SIZE 32
  
  /*
   * Authentication tag length
   */
  #define ENC_AUTHTAG_SIZE 16

  
  /*

   * 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,

  	/* no ->update(); don't add it without changing big_key_crypt() nonce */

  };
  
  /*

   * Crypto names for big_key data authenticated encryption

   */

  static const char big_key_alg_name[] = "gcm(aes)";

  #define BIG_KEY_IV_SIZE		GCM_AES_IV_SIZE

  
  /*

   * Crypto algorithms for big_key data authenticated encryption

   */

  static struct crypto_aead *big_key_aead;

  
  /*

   * Since changing the key affects the entire object, we need a mutex.

   */

  static DEFINE_MUTEX(big_key_aead_lock);

  
  /*
   * Encrypt/decrypt big_key data
   */

  static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)

  {

  	int ret;

  	struct aead_request *aead_req;
  	/* We always use a zero nonce. The reason we can get away with this is
  	 * because we're using a different randomly generated key for every
  	 * different encryption. Notably, too, key_type_big_key doesn't define
  	 * an .update function, so there's no chance we'll wind up reusing the
  	 * key to encrypt updated data. Simply put: one key, one encryption.
  	 */

  	u8 zero_nonce[BIG_KEY_IV_SIZE];

  
  	aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
  	if (!aead_req)
  		return -ENOMEM;
  
  	memset(zero_nonce, 0, sizeof(zero_nonce));

  	aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);

  	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
  	aead_request_set_ad(aead_req, 0);
  
  	mutex_lock(&big_key_aead_lock);
  	if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {

  		ret = -EAGAIN;
  		goto error;
  	}

  	if (op == BIG_KEY_ENC)

  		ret = crypto_aead_encrypt(aead_req);

  	else

  		ret = crypto_aead_decrypt(aead_req);

  error:

  	mutex_unlock(&big_key_aead_lock);
  	aead_request_free(aead_req);

  	return ret;
  }
  
  /*

   * Free up the buffer.
   */
  static void big_key_free_buffer(struct big_key_buf *buf)
  {
  	unsigned int i;
  
  	if (buf->virt) {
  		memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
  		vunmap(buf->virt);
  	}
  
  	for (i = 0; i < buf->nr_pages; i++)
  		if (buf->pages[i])
  			__free_page(buf->pages[i]);
  
  	kfree(buf);
  }
  
  /*
   * Allocate a buffer consisting of a set of pages with a virtual mapping
   * applied over them.
   */
  static void *big_key_alloc_buffer(size_t len)
  {
  	struct big_key_buf *buf;
  	unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	unsigned int i, l;
  
  	buf = kzalloc(sizeof(struct big_key_buf) +
  		      sizeof(struct page) * npg +
  		      sizeof(struct scatterlist) * npg,
  		      GFP_KERNEL);
  	if (!buf)
  		return NULL;
  
  	buf->nr_pages = npg;
  	buf->sg = (void *)(buf->pages + npg);
  	sg_init_table(buf->sg, npg);
  
  	for (i = 0; i < buf->nr_pages; i++) {
  		buf->pages[i] = alloc_page(GFP_KERNEL);
  		if (!buf->pages[i])
  			goto nomem;
  
  		l = min_t(size_t, len, PAGE_SIZE);
  		sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
  		len -= l;
  	}
  
  	buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
  	if (!buf->virt)
  		goto nomem;
  
  	return buf;
  
  nomem:
  	big_key_free_buffer(buf);
  	return NULL;
  }
  
  /*

   * Preparse a big key

   */

  int big_key_preparse(struct key_preparsed_payload *prep)

  {

  	struct big_key_buf *buf;

  	struct path *path = (struct path *)&prep->payload.data[big_key_path];

  	struct file *file;

  	u8 *enckey;

  	ssize_t written;

  	size_t datalen = prep->datalen, enclen = datalen + ENC_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.

  		 */

  		loff_t pos = 0;

  		buf = big_key_alloc_buffer(enclen);
  		if (!buf)

  			return -ENOMEM;

  		memcpy(buf->virt, prep->data, datalen);

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

  		ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
  		if (unlikely(ret))

  			goto err_enckey;
  
  		/* encrypt aligned data */

  		ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);

  		if (ret)
  			goto err_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->virt, enclen, &pos);

  		if (written != enclen) {

  			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
  		 */

  		prep->payload.data[big_key_data] = enckey;

  		*path = file->f_path;
  		path_get(path);
  		fput(file);

  		big_key_free_buffer(buf);

  	} 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:

  	kzfree(enckey);

  error:

  	big_key_free_buffer(buf);

  	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);

  	}

  	kzfree(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;

  	}

  	kzfree(key->payload.data[big_key_data]);

  	key->payload.data[big_key_data] = NULL;

  }
  
  /*
   * 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 __user *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 big_key_buf *buf;

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

  		struct file *file;

  		u8 *enckey = (u8 *)key->payload.data[big_key_data];

  		size_t enclen = datalen + ENC_AUTHTAG_SIZE;

  		loff_t pos = 0;

  		buf = big_key_alloc_buffer(enclen);
  		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->virt, enclen, &pos);

  		if (ret >= 0 && ret != enclen) {

  			ret = -EIO;

  			goto err_fput;
  		}

  		ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);

  		if (ret)
  			goto err_fput;
  
  		ret = datalen;
  
  		/* copy decrypted data to user */

  		if (copy_to_user(buffer, buf->virt, datalen) != 0)

  			ret = -EFAULT;
  
  err_fput:
  		fput(file);
  error:

  		big_key_free_buffer(buf);

  	} else {
  		ret = datalen;

  		if (copy_to_user(buffer, key->payload.data[big_key_data],
  				 datalen) != 0)

  			ret = -EFAULT;
  	}
  
  	return ret;
  }

  /*
   * Register key type
   */

  static int __init big_key_init(void)
  {

  	int ret;

  	/* init block cipher */

  	big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
  	if (IS_ERR(big_key_aead)) {
  		ret = PTR_ERR(big_key_aead);

  		pr_err("Can't alloc crypto: %d
  ", ret);

  		return ret;
  	}

  
  	if (unlikely(crypto_aead_ivsize(big_key_aead) != BIG_KEY_IV_SIZE)) {
  		WARN(1, "big key algorithm changed?");
  		ret = -EINVAL;
  		goto free_aead;
  	}

  	ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
  	if (ret < 0) {
  		pr_err("Can't set crypto auth tag len: %d
  ", ret);
  		goto free_aead;

  	}

  
  	ret = register_key_type(&key_type_big_key);
  	if (ret < 0) {
  		pr_err("Can't register type: %d
  ", ret);

  		goto free_aead;

  	}
  
  	return 0;

  free_aead:
  	crypto_free_aead(big_key_aead);

  	return ret;
  }

  late_initcall(big_key_init);