fs/crypto/crypto.c - kernel/msm - Gitiles

 /*
  * This contains encryption functions for per-file encryption.
  *
  * Copyright (C) 2015, Google, Inc.
  * Copyright (C) 2015, Motorola Mobility
  *
  * Written by Michael Halcrow, 2014.
  *
  * Filename encryption additions
  *	Uday Savagaonkar, 2014
  * Encryption policy handling additions
  *	Ildar Muslukhov, 2014
  * Add fscrypt_pullback_bio_page()
  *	Jaegeuk Kim, 2015.
  *
  * This has not yet undergone a rigorous security audit.
  *
  * The usage of AES-XTS should conform to recommendations in NIST
  * Special Publication 800-38E and IEEE P1619/D16.
  */

 #include <linux/crypto.h>
 #include <linux/ecryptfs.h>
 #include <linux/pagemap.h>
 #include <linux/mempool.h>
 #include <linux/module.h>
 #include <linux/scatterlist.h>
 #include <linux/ratelimit.h>
 #include <linux/bio.h>
 #include <linux/dcache.h>
 #include <linux/namei.h>
 #include <linux/fscrypto.h>

 static unsigned int num_prealloc_crypto_pages = 32;
 static unsigned int num_prealloc_crypto_ctxs = 128;

 module_param(num_prealloc_crypto_pages, uint, 0444);
 MODULE_PARM_DESC(num_prealloc_crypto_pages,
 		"Number of crypto pages to preallocate");
 module_param(num_prealloc_crypto_ctxs, uint, 0444);
 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
 		"Number of crypto contexts to preallocate");

 static mempool_t *fscrypt_bounce_page_pool = NULL;

 static LIST_HEAD(fscrypt_free_ctxs);
 static DEFINE_SPINLOCK(fscrypt_ctx_lock);

 static struct workqueue_struct *fscrypt_read_workqueue;
 static DEFINE_MUTEX(fscrypt_init_mutex);

 static struct kmem_cache *fscrypt_ctx_cachep;
 struct kmem_cache *fscrypt_info_cachep;

 /**
  * fscrypt_release_ctx() - Releases an encryption context
  * @ctx: The encryption context to release.
  *
  * If the encryption context was allocated from the pre-allocated pool, returns
  * it to that pool. Else, frees it.
  *
  * If there's a bounce page in the context, this frees that.
  */
 void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
 {
 	unsigned long flags;

 	if (ctx->flags & FS_WRITE_PATH_FL && ctx->w.bounce_page) {
 		mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
 		ctx->w.bounce_page = NULL;
 	}
 	ctx->w.control_page = NULL;
 	if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
 		kmem_cache_free(fscrypt_ctx_cachep, ctx);
 	} else {
 		spin_lock_irqsave(&fscrypt_ctx_lock, flags);
 		list_add(&ctx->free_list, &fscrypt_free_ctxs);
 		spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
 	}
 }
 EXPORT_SYMBOL(fscrypt_release_ctx);

 /**
  * fscrypt_get_ctx() - Gets an encryption context
  * @inode:       The inode for which we are doing the crypto
  * @gfp_flags:   The gfp flag for memory allocation
  *
  * Allocates and initializes an encryption context.
  *
  * Return: An allocated and initialized encryption context on success; error
  * value or NULL otherwise.
  */
 struct fscrypt_ctx *fscrypt_get_ctx(struct inode *inode, gfp_t gfp_flags)
 {
 	struct fscrypt_ctx *ctx = NULL;
 	struct fscrypt_info *ci = inode->i_crypt_info;
 	unsigned long flags;

 	if (ci == NULL)
 		return ERR_PTR(-ENOKEY);

 	/*
 	 * We first try getting the ctx from a free list because in
 	 * the common case the ctx will have an allocated and
 	 * initialized crypto tfm, so it's probably a worthwhile
 	 * optimization. For the bounce page, we first try getting it
 	 * from the kernel allocator because that's just about as fast
 	 * as getting it from a list and because a cache of free pages
 	 * should generally be a "last resort" option for a filesystem
 	 * to be able to do its job.
 	 */
 	spin_lock_irqsave(&fscrypt_ctx_lock, flags);
 	ctx = list_first_entry_or_null(&fscrypt_free_ctxs,
 					struct fscrypt_ctx, free_list);
 	if (ctx)
 		list_del(&ctx->free_list);
 	spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
 	if (!ctx) {
 		ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, gfp_flags);
 		if (!ctx)
 			return ERR_PTR(-ENOMEM);
 		ctx->flags |= FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 	} else {
 		ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 	}
 	ctx->flags &= ~FS_WRITE_PATH_FL;
 	return ctx;
 }
 EXPORT_SYMBOL(fscrypt_get_ctx);

 /**
  * fscrypt_complete() - The completion callback for page encryption
  * @req: The asynchronous encryption request context
  * @res: The result of the encryption operation
  */
 static void fscrypt_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);
 }

 typedef enum {
 	FS_DECRYPT = 0,
 	FS_ENCRYPT,
 } fscrypt_direction_t;

 static int do_page_crypto(struct inode *inode,
 			fscrypt_direction_t rw, pgoff_t index,
 			struct page *src_page, struct page *dest_page,
 			gfp_t gfp_flags)
 {
 	u8 xts_tweak[FS_XTS_TWEAK_SIZE];
 	struct ablkcipher_request *req = NULL;
 	DECLARE_FS_COMPLETION_RESULT(ecr);
 	struct scatterlist dst, src;
 	struct fscrypt_info *ci = inode->i_crypt_info;
 	struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 	int res = 0;

 	req = ablkcipher_request_alloc(tfm, gfp_flags);
 	if (!req) {
 		printk_ratelimited(KERN_ERR
 				"%s: crypto_request_alloc() failed\n",
 				__func__);
 		return -ENOMEM;
 	}

 	ablkcipher_request_set_callback(
 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		fscrypt_complete, &ecr);

 	BUILD_BUG_ON(FS_XTS_TWEAK_SIZE < sizeof(index));
 	memcpy(xts_tweak, &index, sizeof(index));
 	memset(&xts_tweak[sizeof(index)], 0,
 			FS_XTS_TWEAK_SIZE - sizeof(index));

 	sg_init_table(&dst, 1);
 	sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
 	sg_init_table(&src, 1);
 	sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
 	ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
 					xts_tweak);
 	if (rw == FS_DECRYPT)
 		res = crypto_ablkcipher_decrypt(req);
 	else
 		res = crypto_ablkcipher_encrypt(req);
 	if (res == -EINPROGRESS || res == -EBUSY) {
 		BUG_ON(req->base.data != &ecr);
 		wait_for_completion(&ecr.completion);
 		res = ecr.res;
 	}
 	ablkcipher_request_free(req);
 	if (res) {
 		printk_ratelimited(KERN_ERR
 			"%s: crypto_ablkcipher_encrypt() returned %d\n",
 			__func__, res);
 		return res;
 	}
 	return 0;
 }

 static struct page *alloc_bounce_page(struct fscrypt_ctx *ctx, gfp_t gfp_flags)
 {
 	ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
 	if (ctx->w.bounce_page == NULL)
 		return ERR_PTR(-ENOMEM);
 	ctx->flags |= FS_WRITE_PATH_FL;
 	return ctx->w.bounce_page;
 }

 /**
  * fscypt_encrypt_page() - Encrypts a page
  * @inode:          The inode for which the encryption should take place
  * @plaintext_page: The page to encrypt. Must be locked.
  * @gfp_flags:      The gfp flag for memory allocation
  *
  * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
  * encryption context.
  *
  * Called on the page write path.  The caller must call
  * fscrypt_restore_control_page() on the returned ciphertext page to
  * release the bounce buffer and the encryption context.
  *
  * Return: An allocated page with the encrypted content on success. Else, an
  * error value or NULL.
  */
 struct page *fscrypt_encrypt_page(struct inode *inode,
 				struct page *plaintext_page, gfp_t gfp_flags)
 {
 	struct fscrypt_ctx *ctx;
 	struct page *ciphertext_page = NULL;
 	int err;

 	BUG_ON(!PageLocked(plaintext_page));

 	ctx = fscrypt_get_ctx(inode, gfp_flags);
 	if (IS_ERR(ctx))
 		return (struct page *)ctx;

 	/* The encryption operation will require a bounce page. */
 	ciphertext_page = alloc_bounce_page(ctx, gfp_flags);
 	if (IS_ERR(ciphertext_page))
 		goto errout;

 	ctx->w.control_page = plaintext_page;
 	err = do_page_crypto(inode, FS_ENCRYPT, plaintext_page->index,
 					plaintext_page, ciphertext_page,
 					gfp_flags);
 	if (err) {
 		ciphertext_page = ERR_PTR(err);
 		goto errout;
 	}
 	SetPagePrivate(ciphertext_page);
 	set_page_private(ciphertext_page, (unsigned long)ctx);
 	lock_page(ciphertext_page);
 	return ciphertext_page;

 errout:
 	fscrypt_release_ctx(ctx);
 	return ciphertext_page;
 }
 EXPORT_SYMBOL(fscrypt_encrypt_page);

 /**
  * f2crypt_decrypt_page() - Decrypts a page in-place
  * @page: The page to decrypt. Must be locked.
  *
  * Decrypts page in-place using the ctx encryption context.
  *
  * Called from the read completion callback.
  *
  * Return: Zero on success, non-zero otherwise.
  */
 int fscrypt_decrypt_page(struct page *page)
 {
 	BUG_ON(!PageLocked(page));

 	return do_page_crypto(page->mapping->host,
 			FS_DECRYPT, page->index, page, page, GFP_NOFS);
 }
 EXPORT_SYMBOL(fscrypt_decrypt_page);

 int fscrypt_zeroout_range(struct inode *inode, pgoff_t lblk,
 				sector_t pblk, unsigned int len)
 {
 	struct fscrypt_ctx *ctx;
 	struct page *ciphertext_page = NULL;
 	struct bio *bio;
 	int ret, err = 0;

 	BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);

 	ctx = fscrypt_get_ctx(inode, GFP_NOFS);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);

 	ciphertext_page = alloc_bounce_page(ctx, GFP_NOWAIT);
 	if (IS_ERR(ciphertext_page)) {
 		err = PTR_ERR(ciphertext_page);
 		goto errout;
 	}

 	while (len--) {
 		err = do_page_crypto(inode, FS_ENCRYPT, lblk,
 					ZERO_PAGE(0), ciphertext_page,
 					GFP_NOFS);
 		if (err)
 			goto errout;

 		bio = bio_alloc(GFP_NOWAIT, 1);
 		if (!bio) {
 			err = -ENOMEM;
 			goto errout;
 		}
 		bio->bi_bdev = inode->i_sb->s_bdev;
 		bio->bi_sector =
 			pblk << (inode->i_sb->s_blocksize_bits - 9);
 		ret = bio_add_page(bio, ciphertext_page,
 					inode->i_sb->s_blocksize, 0);
 		if (ret != inode->i_sb->s_blocksize) {
 			/* should never happen! */
 			WARN_ON(1);
 			bio_put(bio);
 			err = -EIO;
 			goto errout;
 		}
 		err = submit_bio_wait(WRITE, bio);
 		bio_put(bio);
 		if (err)
 			goto errout;
 		lblk++;
 		pblk++;
 	}
 	err = 0;
 errout:
 	fscrypt_release_ctx(ctx);
 	return err;
 }
 EXPORT_SYMBOL(fscrypt_zeroout_range);

 /*
  * Validate dentries for encrypted directories to make sure we aren't
  * potentially caching stale data after a key has been added or
  * removed.
  */
 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 {
 	struct dentry *dir;
 	struct fscrypt_info *ci;
 	int dir_has_key, cached_with_key;

 	if (flags & LOOKUP_RCU)
 		return -ECHILD;

 	dir = dget_parent(dentry);
 	if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
 		dput(dir);
 		return 0;
 	}

 	ci = d_inode(dir)->i_crypt_info;
 	if (ci && ci->ci_keyring_key &&
 	    (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 					  (1 << KEY_FLAG_REVOKED) |
 					  (1 << KEY_FLAG_DEAD))))
 		ci = NULL;

 	/* this should eventually be an flag in d_flags */
 	spin_lock(&dentry->d_lock);
 	cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
 	spin_unlock(&dentry->d_lock);
 	dir_has_key = (ci != NULL);
 	dput(dir);

 	/*
 	 * If the dentry was cached without the key, and it is a
 	 * negative dentry, it might be a valid name.  We can't check
 	 * if the key has since been made available due to locking
 	 * reasons, so we fail the validation so ext4_lookup() can do
 	 * this check.
 	 *
 	 * We also fail the validation if the dentry was created with
 	 * the key present, but we no longer have the key, or vice versa.
 	 */
 	if (!cached_with_key ||
 			(!cached_with_key && dir_has_key) ||
 			(cached_with_key && !dir_has_key))
 		return 0;
 	return 1;
 }

 const struct dentry_operations fscrypt_d_ops = {
 	.d_revalidate = fscrypt_d_revalidate,
 };
 EXPORT_SYMBOL(fscrypt_d_ops);

 /*
  * Call fscrypt_decrypt_page on every single page, reusing the encryption
  * context.
  */
 static void completion_pages(struct work_struct *work)
 {
 	struct fscrypt_ctx *ctx =
 		container_of(work, struct fscrypt_ctx, r.work);
 	struct bio *bio = ctx->r.bio;
 	struct bio_vec *bv;
 	int i;

 	bio_for_each_segment_all(bv, bio, i) {
 		struct page *page = bv->bv_page;
 		int ret = fscrypt_decrypt_page(page);

 		if (ret) {
 			WARN_ON_ONCE(1);
 			SetPageError(page);
 		} else {
 			SetPageUptodate(page);
 		}
 		unlock_page(page);
 	}
 	fscrypt_release_ctx(ctx);
 	bio_put(bio);
 }

 void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *ctx, struct bio *bio)
 {
 	INIT_WORK(&ctx->r.work, completion_pages);
 	ctx->r.bio = bio;
 	queue_work(fscrypt_read_workqueue, &ctx->r.work);
 }
 EXPORT_SYMBOL(fscrypt_decrypt_bio_pages);

 void fscrypt_pullback_bio_page(struct page **page, bool restore)
 {
 	struct fscrypt_ctx *ctx;
 	struct page *bounce_page;

 	/* The bounce data pages are unmapped. */
 	if ((*page)->mapping)
 		return;

 	/* The bounce data page is unmapped. */
 	bounce_page = *page;
 	ctx = (struct fscrypt_ctx *)page_private(bounce_page);

 	/* restore control page */
 	*page = ctx->w.control_page;

 	if (restore)
 		fscrypt_restore_control_page(bounce_page);
 }
 EXPORT_SYMBOL(fscrypt_pullback_bio_page);

 void fscrypt_restore_control_page(struct page *page)
 {
 	struct fscrypt_ctx *ctx;

 	ctx = (struct fscrypt_ctx *)page_private(page);
 	set_page_private(page, (unsigned long)NULL);
 	ClearPagePrivate(page);
 	unlock_page(page);
 	fscrypt_release_ctx(ctx);
 }
 EXPORT_SYMBOL(fscrypt_restore_control_page);

 static void fscrypt_destroy(void)
 {
 	struct fscrypt_ctx *pos, *n;

 	list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
 		kmem_cache_free(fscrypt_ctx_cachep, pos);
 	INIT_LIST_HEAD(&fscrypt_free_ctxs);
 	mempool_destroy(fscrypt_bounce_page_pool);
 	fscrypt_bounce_page_pool = NULL;
 }

 /**
  * fscrypt_initialize() - allocate major buffers for fs encryption.
  *
  * We only call this when we start accessing encrypted files, since it
  * results in memory getting allocated that wouldn't otherwise be used.
  *
  * Return: Zero on success, non-zero otherwise.
  */
 int fscrypt_initialize(void)
 {
 	int i, res = -ENOMEM;

 	if (fscrypt_bounce_page_pool)
 		return 0;

 	mutex_lock(&fscrypt_init_mutex);
 	if (fscrypt_bounce_page_pool)
 		goto already_initialized;

 	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 		struct fscrypt_ctx *ctx;

 		ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
 		if (!ctx)
 			goto fail;
 		list_add(&ctx->free_list, &fscrypt_free_ctxs);
 	}

 	fscrypt_bounce_page_pool =
 		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 	if (!fscrypt_bounce_page_pool)
 		goto fail;

 already_initialized:
 	mutex_unlock(&fscrypt_init_mutex);
 	return 0;
 fail:
 	fscrypt_destroy();
 	mutex_unlock(&fscrypt_init_mutex);
 	return res;
 }
 EXPORT_SYMBOL(fscrypt_initialize);

 /**
  * fscrypt_init() - Set up for fs encryption.
  */
 static int __init fscrypt_init(void)
 {
 	fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
 							WQ_HIGHPRI, 0);
 	if (!fscrypt_read_workqueue)
 		goto fail;

 	fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
 	if (!fscrypt_ctx_cachep)
 		goto fail_free_queue;

 	fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
 	if (!fscrypt_info_cachep)
 		goto fail_free_ctx;

 	return 0;

 fail_free_ctx:
 	kmem_cache_destroy(fscrypt_ctx_cachep);
 fail_free_queue:
 	destroy_workqueue(fscrypt_read_workqueue);
 fail:
 	return -ENOMEM;
 }
 module_init(fscrypt_init)

 /**
  * fscrypt_exit() - Shutdown the fs encryption system
  */
 static void __exit fscrypt_exit(void)
 {
 	fscrypt_destroy();

 	if (fscrypt_read_workqueue)
 		destroy_workqueue(fscrypt_read_workqueue);
 	kmem_cache_destroy(fscrypt_ctx_cachep);
 	kmem_cache_destroy(fscrypt_info_cachep);
 }
 module_exit(fscrypt_exit);

 MODULE_LICENSE("GPL");
	/*
	* This contains encryption functions for per-file encryption.
	*
	* Copyright (C) 2015, Google, Inc.
	* Copyright (C) 2015, Motorola Mobility
	*
	* Written by Michael Halcrow, 2014.
	*
	* Filename encryption additions
	* Uday Savagaonkar, 2014
	* Encryption policy handling additions
	* Ildar Muslukhov, 2014
	* Add fscrypt_pullback_bio_page()
	* Jaegeuk Kim, 2015.
	*
	* This has not yet undergone a rigorous security audit.
	*
	* The usage of AES-XTS should conform to recommendations in NIST
	* Special Publication 800-38E and IEEE P1619/D16.
	*/

	#include <linux/crypto.h>
	#include <linux/ecryptfs.h>
	#include <linux/pagemap.h>
	#include <linux/mempool.h>
	#include <linux/module.h>
	#include <linux/scatterlist.h>
	#include <linux/ratelimit.h>
	#include <linux/bio.h>
	#include <linux/dcache.h>
	#include <linux/namei.h>
	#include <linux/fscrypto.h>

	static unsigned int num_prealloc_crypto_pages = 32;
	static unsigned int num_prealloc_crypto_ctxs = 128;

	module_param(num_prealloc_crypto_pages, uint, 0444);
	MODULE_PARM_DESC(num_prealloc_crypto_pages,
	"Number of crypto pages to preallocate");
	module_param(num_prealloc_crypto_ctxs, uint, 0444);
	MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
	"Number of crypto contexts to preallocate");

	static mempool_t *fscrypt_bounce_page_pool = NULL;

	static LIST_HEAD(fscrypt_free_ctxs);
	static DEFINE_SPINLOCK(fscrypt_ctx_lock);

	static struct workqueue_struct *fscrypt_read_workqueue;
	static DEFINE_MUTEX(fscrypt_init_mutex);

	static struct kmem_cache *fscrypt_ctx_cachep;
	struct kmem_cache *fscrypt_info_cachep;

	/**
	* fscrypt_release_ctx() - Releases an encryption context
	* @ctx: The encryption context to release.
	*
	* If the encryption context was allocated from the pre-allocated pool, returns
	* it to that pool. Else, frees it.
	*
	* If there's a bounce page in the context, this frees that.
	*/
	void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
	{
	unsigned long flags;

	if (ctx->flags & FS_WRITE_PATH_FL && ctx->w.bounce_page) {
	mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
	ctx->w.bounce_page = NULL;
	}
	ctx->w.control_page = NULL;
	if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
	kmem_cache_free(fscrypt_ctx_cachep, ctx);
	} else {
	spin_lock_irqsave(&fscrypt_ctx_lock, flags);
	list_add(&ctx->free_list, &fscrypt_free_ctxs);
	spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
	}
	}
	EXPORT_SYMBOL(fscrypt_release_ctx);

	/**
	* fscrypt_get_ctx() - Gets an encryption context
	* @inode: The inode for which we are doing the crypto
	* @gfp_flags: The gfp flag for memory allocation
	*
	* Allocates and initializes an encryption context.
	*
	* Return: An allocated and initialized encryption context on success; error
	* value or NULL otherwise.
	*/
	struct fscrypt_ctx fscrypt_get_ctx(struct inode inode, gfp_t gfp_flags)
	{
	struct fscrypt_ctx *ctx = NULL;
	struct fscrypt_info *ci = inode->i_crypt_info;
	unsigned long flags;

	if (ci == NULL)
	return ERR_PTR(-ENOKEY);

	/*
	* We first try getting the ctx from a free list because in
	* the common case the ctx will have an allocated and
	* initialized crypto tfm, so it's probably a worthwhile
	* optimization. For the bounce page, we first try getting it
	* from the kernel allocator because that's just about as fast
	* as getting it from a list and because a cache of free pages
	* should generally be a "last resort" option for a filesystem
	* to be able to do its job.
	*/
	spin_lock_irqsave(&fscrypt_ctx_lock, flags);
	ctx = list_first_entry_or_null(&fscrypt_free_ctxs,
	struct fscrypt_ctx, free_list);
	if (ctx)
	list_del(&ctx->free_list);
	spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
	if (!ctx) {
	ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, gfp_flags);
	if (!ctx)
	return ERR_PTR(-ENOMEM);
	ctx->flags \|= FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
	} else {
	ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
	}
	ctx->flags &= ~FS_WRITE_PATH_FL;
	return ctx;
	}
	EXPORT_SYMBOL(fscrypt_get_ctx);

	/**
	* fscrypt_complete() - The completion callback for page encryption
	* @req: The asynchronous encryption request context
	* @res: The result of the encryption operation
	*/
	static void fscrypt_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);
	}

	typedef enum {
	FS_DECRYPT = 0,
	FS_ENCRYPT,
	} fscrypt_direction_t;

	static int do_page_crypto(struct inode *inode,
	fscrypt_direction_t rw, pgoff_t index,
	struct page src_page, struct page dest_page,
	gfp_t gfp_flags)
	{
	u8 xts_tweak[FS_XTS_TWEAK_SIZE];
	struct ablkcipher_request *req = NULL;
	DECLARE_FS_COMPLETION_RESULT(ecr);
	struct scatterlist dst, src;
	struct fscrypt_info *ci = inode->i_crypt_info;
	struct crypto_ablkcipher *tfm = ci->ci_ctfm;
	int res = 0;

	req = ablkcipher_request_alloc(tfm, gfp_flags);
	if (!req) {
	printk_ratelimited(KERN_ERR
	"%s: crypto_request_alloc() failed\n",
	__func__);
	return -ENOMEM;
	}

	ablkcipher_request_set_callback(
	req, CRYPTO_TFM_REQ_MAY_BACKLOG \| CRYPTO_TFM_REQ_MAY_SLEEP,
	fscrypt_complete, &ecr);

	BUILD_BUG_ON(FS_XTS_TWEAK_SIZE < sizeof(index));
	memcpy(xts_tweak, &index, sizeof(index));
	memset(&xts_tweak[sizeof(index)], 0,
	FS_XTS_TWEAK_SIZE - sizeof(index));

	sg_init_table(&dst, 1);
	sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
	sg_init_table(&src, 1);
	sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
	ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
	xts_tweak);
	if (rw == FS_DECRYPT)
	res = crypto_ablkcipher_decrypt(req);
	else
	res = crypto_ablkcipher_encrypt(req);
	if (res == -EINPROGRESS \|\| res == -EBUSY) {
	BUG_ON(req->base.data != &ecr);
	wait_for_completion(&ecr.completion);
	res = ecr.res;
	}
	ablkcipher_request_free(req);
	if (res) {
	printk_ratelimited(KERN_ERR
	"%s: crypto_ablkcipher_encrypt() returned %d\n",
	__func__, res);
	return res;
	}
	return 0;
	}

	static struct page alloc_bounce_page(struct fscrypt_ctx ctx, gfp_t gfp_flags)
	{
	ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
	if (ctx->w.bounce_page == NULL)
	return ERR_PTR(-ENOMEM);
	ctx->flags \|= FS_WRITE_PATH_FL;
	return ctx->w.bounce_page;
	}

	/**
	* fscypt_encrypt_page() - Encrypts a page
	* @inode: The inode for which the encryption should take place
	* @plaintext_page: The page to encrypt. Must be locked.
	* @gfp_flags: The gfp flag for memory allocation
	*
	* Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
	* encryption context.
	*
	* Called on the page write path. The caller must call
	* fscrypt_restore_control_page() on the returned ciphertext page to
	* release the bounce buffer and the encryption context.
	*
	* Return: An allocated page with the encrypted content on success. Else, an
	* error value or NULL.
	*/
	struct page fscrypt_encrypt_page(struct inode inode,
	struct page *plaintext_page, gfp_t gfp_flags)
	{
	struct fscrypt_ctx *ctx;
	struct page *ciphertext_page = NULL;
	int err;

	BUG_ON(!PageLocked(plaintext_page));

	ctx = fscrypt_get_ctx(inode, gfp_flags);
	if (IS_ERR(ctx))
	return (struct page *)ctx;

	/* The encryption operation will require a bounce page. */
	ciphertext_page = alloc_bounce_page(ctx, gfp_flags);
	if (IS_ERR(ciphertext_page))
	goto errout;

	ctx->w.control_page = plaintext_page;
	err = do_page_crypto(inode, FS_ENCRYPT, plaintext_page->index,
	plaintext_page, ciphertext_page,
	gfp_flags);
	if (err) {
	ciphertext_page = ERR_PTR(err);
	goto errout;
	}
	SetPagePrivate(ciphertext_page);
	set_page_private(ciphertext_page, (unsigned long)ctx);
	lock_page(ciphertext_page);
	return ciphertext_page;

	errout:
	fscrypt_release_ctx(ctx);
	return ciphertext_page;
	}
	EXPORT_SYMBOL(fscrypt_encrypt_page);

	/**
	* f2crypt_decrypt_page() - Decrypts a page in-place
	* @page: The page to decrypt. Must be locked.
	*
	* Decrypts page in-place using the ctx encryption context.
	*
	* Called from the read completion callback.
	*
	* Return: Zero on success, non-zero otherwise.
	*/
	int fscrypt_decrypt_page(struct page *page)
	{
	BUG_ON(!PageLocked(page));

	return do_page_crypto(page->mapping->host,
	FS_DECRYPT, page->index, page, page, GFP_NOFS);
	}
	EXPORT_SYMBOL(fscrypt_decrypt_page);

	int fscrypt_zeroout_range(struct inode *inode, pgoff_t lblk,
	sector_t pblk, unsigned int len)
	{
	struct fscrypt_ctx *ctx;
	struct page *ciphertext_page = NULL;
	struct bio *bio;
	int ret, err = 0;

	BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);

	ctx = fscrypt_get_ctx(inode, GFP_NOFS);
	if (IS_ERR(ctx))
	return PTR_ERR(ctx);

	ciphertext_page = alloc_bounce_page(ctx, GFP_NOWAIT);
	if (IS_ERR(ciphertext_page)) {
	err = PTR_ERR(ciphertext_page);
	goto errout;
	}

	while (len--) {
	err = do_page_crypto(inode, FS_ENCRYPT, lblk,
	ZERO_PAGE(0), ciphertext_page,
	GFP_NOFS);
	if (err)
	goto errout;

	bio = bio_alloc(GFP_NOWAIT, 1);
	if (!bio) {
	err = -ENOMEM;
	goto errout;
	}
	bio->bi_bdev = inode->i_sb->s_bdev;
	bio->bi_sector =
	pblk << (inode->i_sb->s_blocksize_bits - 9);
	ret = bio_add_page(bio, ciphertext_page,
	inode->i_sb->s_blocksize, 0);
	if (ret != inode->i_sb->s_blocksize) {
	/* should never happen! */
	WARN_ON(1);
	bio_put(bio);
	err = -EIO;
	goto errout;
	}
	err = submit_bio_wait(WRITE, bio);
	bio_put(bio);
	if (err)
	goto errout;
	lblk++;
	pblk++;
	}
	err = 0;
	errout:
	fscrypt_release_ctx(ctx);
	return err;
	}
	EXPORT_SYMBOL(fscrypt_zeroout_range);

	/*
	* Validate dentries for encrypted directories to make sure we aren't
	* potentially caching stale data after a key has been added or
	* removed.
	*/
	static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
	{
	struct dentry *dir;
	struct fscrypt_info *ci;
	int dir_has_key, cached_with_key;

	if (flags & LOOKUP_RCU)
	return -ECHILD;

	dir = dget_parent(dentry);
	if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
	dput(dir);
	return 0;
	}

	ci = d_inode(dir)->i_crypt_info;
	if (ci && ci->ci_keyring_key &&
	(ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) \|
	(1 << KEY_FLAG_REVOKED) \|
	(1 << KEY_FLAG_DEAD))))
	ci = NULL;

	/* this should eventually be an flag in d_flags */
	spin_lock(&dentry->d_lock);
	cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
	spin_unlock(&dentry->d_lock);
	dir_has_key = (ci != NULL);
	dput(dir);

	/*
	* If the dentry was cached without the key, and it is a
	* negative dentry, it might be a valid name. We can't check
	* if the key has since been made available due to locking
	* reasons, so we fail the validation so ext4_lookup() can do
	* this check.
	*
	* We also fail the validation if the dentry was created with
	* the key present, but we no longer have the key, or vice versa.
	*/
	if (!cached_with_key \|\|
	(!cached_with_key && dir_has_key) \|\|
	(cached_with_key && !dir_has_key))
	return 0;
	return 1;
	}

	const struct dentry_operations fscrypt_d_ops = {
	.d_revalidate = fscrypt_d_revalidate,
	};
	EXPORT_SYMBOL(fscrypt_d_ops);

	/*
	* Call fscrypt_decrypt_page on every single page, reusing the encryption
	* context.
	*/
	static void completion_pages(struct work_struct *work)
	{
	struct fscrypt_ctx *ctx =
	container_of(work, struct fscrypt_ctx, r.work);
	struct bio *bio = ctx->r.bio;
	struct bio_vec *bv;
	int i;

	bio_for_each_segment_all(bv, bio, i) {
	struct page *page = bv->bv_page;
	int ret = fscrypt_decrypt_page(page);

	if (ret) {
	WARN_ON_ONCE(1);
	SetPageError(page);
	} else {
	SetPageUptodate(page);
	}
	unlock_page(page);
	}
	fscrypt_release_ctx(ctx);
	bio_put(bio);
	}

	void fscrypt_decrypt_bio_pages(struct fscrypt_ctx ctx, struct bio bio)
	{
	INIT_WORK(&ctx->r.work, completion_pages);
	ctx->r.bio = bio;
	queue_work(fscrypt_read_workqueue, &ctx->r.work);
	}
	EXPORT_SYMBOL(fscrypt_decrypt_bio_pages);

	void fscrypt_pullback_bio_page(struct page **page, bool restore)
	{
	struct fscrypt_ctx *ctx;
	struct page *bounce_page;

	/* The bounce data pages are unmapped. */
	if ((*page)->mapping)
	return;

	/* The bounce data page is unmapped. */
	bounce_page = *page;
	ctx = (struct fscrypt_ctx *)page_private(bounce_page);

	/* restore control page */
	*page = ctx->w.control_page;

	if (restore)
	fscrypt_restore_control_page(bounce_page);
	}
	EXPORT_SYMBOL(fscrypt_pullback_bio_page);

	void fscrypt_restore_control_page(struct page *page)
	{
	struct fscrypt_ctx *ctx;

	ctx = (struct fscrypt_ctx *)page_private(page);
	set_page_private(page, (unsigned long)NULL);
	ClearPagePrivate(page);
	unlock_page(page);
	fscrypt_release_ctx(ctx);
	}
	EXPORT_SYMBOL(fscrypt_restore_control_page);

	static void fscrypt_destroy(void)
	{
	struct fscrypt_ctx pos, n;

	list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
	kmem_cache_free(fscrypt_ctx_cachep, pos);
	INIT_LIST_HEAD(&fscrypt_free_ctxs);
	mempool_destroy(fscrypt_bounce_page_pool);
	fscrypt_bounce_page_pool = NULL;
	}

	/**
	* fscrypt_initialize() - allocate major buffers for fs encryption.
	*
	* We only call this when we start accessing encrypted files, since it
	* results in memory getting allocated that wouldn't otherwise be used.
	*
	* Return: Zero on success, non-zero otherwise.
	*/
	int fscrypt_initialize(void)
	{
	int i, res = -ENOMEM;

	if (fscrypt_bounce_page_pool)
	return 0;

	mutex_lock(&fscrypt_init_mutex);
	if (fscrypt_bounce_page_pool)
	goto already_initialized;

	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
	struct fscrypt_ctx *ctx;

	ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
	if (!ctx)
	goto fail;
	list_add(&ctx->free_list, &fscrypt_free_ctxs);
	}

	fscrypt_bounce_page_pool =
	mempool_create_page_pool(num_prealloc_crypto_pages, 0);
	if (!fscrypt_bounce_page_pool)
	goto fail;

	already_initialized:
	mutex_unlock(&fscrypt_init_mutex);
	return 0;
	fail:
	fscrypt_destroy();
	mutex_unlock(&fscrypt_init_mutex);
	return res;
	}
	EXPORT_SYMBOL(fscrypt_initialize);

	/**
	* fscrypt_init() - Set up for fs encryption.
	*/
	static int __init fscrypt_init(void)
	{
	fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
	WQ_HIGHPRI, 0);
	if (!fscrypt_read_workqueue)
	goto fail;

	fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
	if (!fscrypt_ctx_cachep)
	goto fail_free_queue;

	fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
	if (!fscrypt_info_cachep)
	goto fail_free_ctx;

	return 0;

	fail_free_ctx:
	kmem_cache_destroy(fscrypt_ctx_cachep);
	fail_free_queue:
	destroy_workqueue(fscrypt_read_workqueue);
	fail:
	return -ENOMEM;
	}
	module_init(fscrypt_init)

	/**
	* fscrypt_exit() - Shutdown the fs encryption system
	*/
	static void __exit fscrypt_exit(void)
	{
	fscrypt_destroy();

	if (fscrypt_read_workqueue)
	destroy_workqueue(fscrypt_read_workqueue);
	kmem_cache_destroy(fscrypt_ctx_cachep);
	kmem_cache_destroy(fscrypt_info_cachep);
	}
	module_exit(fscrypt_exit);

	MODULE_LICENSE("GPL");