ext4 crypto: add ext4 encryption facilities

On encrypt, we will re-assign the buffer_heads to point to a bounce
page rather than the control_page (which is the original page to write
that contains the plaintext). The block I/O occurs against the bounce
page.  On write completion, we re-assign the buffer_heads to the
original plaintext page.

On decrypt, we will attach a read completion callback to the bio
struct. This read completion will decrypt the read contents in-place
prior to setting the page up-to-date.

The current encryption mode, AES-256-XTS, lacks cryptographic
integrity. AES-256-GCM is in-plan, but we will need to devise a
mechanism for handling the integrity data.

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <ildarm@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 558 insertions, 0 deletions

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
new file mode 100644
index 0000000..8ff1527
--- /dev/null
+++ b/fs/ext4/crypto.c
@@ -0,0 +1,558 @@
+/*
+ * linux/fs/ext4/crypto.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption functions for ext4
+ *
+ * Written by Michael Halcrow, 2014.
+ *
+ * Filename encryption additions
+ *	Uday Savagaonkar, 2014
+ * Encryption policy handling additions
+ *	Ildar Muslukhov, 2014
+ *
+ * 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 <crypto/hash.h>
+#include <crypto/sha.h>
+#include <keys/user-type.h>
+#include <keys/encrypted-type.h>
+#include <linux/crypto.h>
+#include <linux/ecryptfs.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/key.h>
+#include <linux/list.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+#include <linux/spinlock_types.h>
+
+#include "ext4_extents.h"
+#include "xattr.h"
+
+/* Encryption added and removed here! (L: */
+
+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 *ext4_bounce_page_pool;
+
+static LIST_HEAD(ext4_free_crypto_ctxs);
+static DEFINE_SPINLOCK(ext4_crypto_ctx_lock);
+
+/**
+ * ext4_release_crypto_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 ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
+{
+	unsigned long flags;
+
+	if (ctx->bounce_page) {
+		if (ctx->flags & EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL)
+			__free_page(ctx->bounce_page);
+		else
+			mempool_free(ctx->bounce_page, ext4_bounce_page_pool);
+		ctx->bounce_page = NULL;
+	}
+	ctx->control_page = NULL;
+	if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
+		if (ctx->tfm)
+			crypto_free_tfm(ctx->tfm);
+		kfree(ctx);
+	} else {
+		spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
+		list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
+		spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
+	}
+}
+
+/**
+ * ext4_alloc_and_init_crypto_ctx() - Allocates and inits an encryption context
+ * @mask: The allocation mask.
+ *
+ * Return: An allocated and initialized encryption context on success. An error
+ * value or NULL otherwise.
+ */
+static struct ext4_crypto_ctx *ext4_alloc_and_init_crypto_ctx(gfp_t mask)
+{
+	struct ext4_crypto_ctx *ctx = kzalloc(sizeof(struct ext4_crypto_ctx),
+					      mask);
+
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+	return ctx;
+}
+
+/**
+ * ext4_get_crypto_ctx() - Gets an encryption context
+ * @inode:       The inode for which we are doing the crypto
+ *
+ * Allocates and initializes an encryption context.
+ *
+ * Return: An allocated and initialized encryption context on success; error
+ * value or NULL otherwise.
+ */
+struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
+{
+	struct ext4_crypto_ctx *ctx = NULL;
+	int res = 0;
+	unsigned long flags;
+	struct ext4_encryption_key *key = &EXT4_I(inode)->i_encryption_key;
+
+	if (!ext4_read_workqueue)
+		ext4_init_crypto();
+
+	/*
+	 * 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(&ext4_crypto_ctx_lock, flags);
+	ctx = list_first_entry_or_null(&ext4_free_crypto_ctxs,
+				       struct ext4_crypto_ctx, free_list);
+	if (ctx)
+		list_del(&ctx->free_list);
+	spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
+	if (!ctx) {
+		ctx = ext4_alloc_and_init_crypto_ctx(GFP_NOFS);
+		if (IS_ERR(ctx)) {
+			res = PTR_ERR(ctx);
+			goto out;
+		}
+		ctx->flags |= EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
+	} else {
+		ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
+	}
+
+	/* Allocate a new Crypto API context if we don't already have
+	 * one or if it isn't the right mode. */
+	BUG_ON(key->mode == EXT4_ENCRYPTION_MODE_INVALID);
+	if (ctx->tfm && (ctx->mode != key->mode)) {
+		crypto_free_tfm(ctx->tfm);
+		ctx->tfm = NULL;
+		ctx->mode = EXT4_ENCRYPTION_MODE_INVALID;
+	}
+	if (!ctx->tfm) {
+		switch (key->mode) {
+		case EXT4_ENCRYPTION_MODE_AES_256_XTS:
+			ctx->tfm = crypto_ablkcipher_tfm(
+				crypto_alloc_ablkcipher("xts(aes)", 0, 0));
+			break;
+		case EXT4_ENCRYPTION_MODE_AES_256_GCM:
+			/* TODO(mhalcrow): AEAD w/ gcm(aes);
+			 * crypto_aead_setauthsize() */
+			ctx->tfm = ERR_PTR(-ENOTSUPP);
+			break;
+		default:
+			BUG();
+		}
+		if (IS_ERR_OR_NULL(ctx->tfm)) {
+			res = PTR_ERR(ctx->tfm);
+			ctx->tfm = NULL;
+			goto out;
+		}
+		ctx->mode = key->mode;
+	}
+	BUG_ON(key->size != ext4_encryption_key_size(key->mode));
+
+	/* There shouldn't be a bounce page attached to the crypto
+	 * context at this point. */
+	BUG_ON(ctx->bounce_page);
+
+out:
+	if (res) {
+		if (!IS_ERR_OR_NULL(ctx))
+			ext4_release_crypto_ctx(ctx);
+		ctx = ERR_PTR(res);
+	}
+	return ctx;
+}
+
+struct workqueue_struct *ext4_read_workqueue;
+static DEFINE_MUTEX(crypto_init);
+
+/**
+ * ext4_exit_crypto() - Shutdown the ext4 encryption system
+ */
+void ext4_exit_crypto(void)
+{
+	struct ext4_crypto_ctx *pos, *n;
+
+	list_for_each_entry_safe(pos, n, &ext4_free_crypto_ctxs, free_list) {
+		if (pos->bounce_page) {
+			if (pos->flags &
+			    EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL) {
+				__free_page(pos->bounce_page);
+			} else {
+				mempool_free(pos->bounce_page,
+					     ext4_bounce_page_pool);
+			}
+		}
+		if (pos->tfm)
+			crypto_free_tfm(pos->tfm);
+		kfree(pos);
+	}
+	INIT_LIST_HEAD(&ext4_free_crypto_ctxs);
+	if (ext4_bounce_page_pool)
+		mempool_destroy(ext4_bounce_page_pool);
+	ext4_bounce_page_pool = NULL;
+	if (ext4_read_workqueue)
+		destroy_workqueue(ext4_read_workqueue);
+	ext4_read_workqueue = NULL;
+}
+
+/**
+ * ext4_init_crypto() - Set up for ext4 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 ext4_init_crypto(void)
+{
+	int i, res;
+
+	mutex_lock(&crypto_init);
+	if (ext4_read_workqueue)
+		goto already_initialized;
+	ext4_read_workqueue = alloc_workqueue("ext4_crypto", WQ_HIGHPRI, 0);
+	if (!ext4_read_workqueue) {
+		res = -ENOMEM;
+		goto fail;
+	}
+
+	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
+		struct ext4_crypto_ctx *ctx;
+
+		ctx = ext4_alloc_and_init_crypto_ctx(GFP_KERNEL);
+		if (IS_ERR(ctx)) {
+			res = PTR_ERR(ctx);
+			goto fail;
+		}
+		list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
+	}
+
+	ext4_bounce_page_pool =
+		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
+	if (!ext4_bounce_page_pool) {
+		res = -ENOMEM;
+		goto fail;
+	}
+already_initialized:
+	mutex_unlock(&crypto_init);
+	return 0;
+fail:
+	ext4_exit_crypto();
+	mutex_unlock(&crypto_init);
+	return res;
+}
+
+void ext4_restore_control_page(struct page *data_page)
+{
+	struct ext4_crypto_ctx *ctx =
+		(struct ext4_crypto_ctx *)page_private(data_page);
+
+	set_page_private(data_page, (unsigned long)NULL);
+	ClearPagePrivate(data_page);
+	unlock_page(data_page);
+	ext4_release_crypto_ctx(ctx);
+}
+
+/**
+ * ext4_crypt_complete() - The completion callback for page encryption
+ * @req: The asynchronous encryption request context
+ * @res: The result of the encryption operation
+ */
+static void ext4_crypt_complete(struct crypto_async_request *req, int res)
+{
+	struct ext4_completion_result *ecr = req->data;
+
+	if (res == -EINPROGRESS)
+		return;
+	ecr->res = res;
+	complete(&ecr->completion);
+}
+
+typedef enum {
+	EXT4_DECRYPT = 0,
+	EXT4_ENCRYPT,
+} ext4_direction_t;
+
+static int ext4_page_crypto(struct ext4_crypto_ctx *ctx,
+			    struct inode *inode,
+			    ext4_direction_t rw,
+			    pgoff_t index,
+			    struct page *src_page,
+			    struct page *dest_page)
+
+{
+	u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
+	struct ablkcipher_request *req = NULL;
+	DECLARE_EXT4_COMPLETION_RESULT(ecr);
+	struct scatterlist dst, src;
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct crypto_ablkcipher *atfm = __crypto_ablkcipher_cast(ctx->tfm);
+	int res = 0;
+
+	BUG_ON(!ctx->tfm);
+	BUG_ON(ctx->mode != ei->i_encryption_key.mode);
+
+	if (ctx->mode != EXT4_ENCRYPTION_MODE_AES_256_XTS) {
+		printk_ratelimited(KERN_ERR
+				   "%s: unsupported crypto algorithm: %d\n",
+				   __func__, ctx->mode);
+		return -ENOTSUPP;
+	}
+
+	crypto_ablkcipher_clear_flags(atfm, ~0);
+	crypto_tfm_set_flags(ctx->tfm, CRYPTO_TFM_REQ_WEAK_KEY);
+
+	res = crypto_ablkcipher_setkey(atfm, ei->i_encryption_key.raw,
+				       ei->i_encryption_key.size);
+	if (res) {
+		printk_ratelimited(KERN_ERR
+				   "%s: crypto_ablkcipher_setkey() failed\n",
+				   __func__);
+		return res;
+	}
+	req = ablkcipher_request_alloc(atfm, GFP_NOFS);
+	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,
+		ext4_crypt_complete, &ecr);
+
+	BUILD_BUG_ON(EXT4_XTS_TWEAK_SIZE < sizeof(index));
+	memcpy(xts_tweak, &index, sizeof(index));
+	memset(&xts_tweak[sizeof(index)], 0,
+	       EXT4_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 == EXT4_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;
+}
+
+/**
+ * ext4_encrypt() - Encrypts a page
+ * @inode:          The inode for which the encryption should take place
+ * @plaintext_page: The page to encrypt. Must be locked.
+ *
+ * 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
+ * ext4_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 *ext4_encrypt(struct inode *inode,
+			  struct page *plaintext_page)
+{
+	struct ext4_crypto_ctx *ctx;
+	struct page *ciphertext_page = NULL;
+	int err;
+
+	BUG_ON(!PageLocked(plaintext_page));
+
+	ctx = ext4_get_crypto_ctx(inode);
+	if (IS_ERR(ctx))
+		return (struct page *) ctx;
+
+	/* The encryption operation will require a bounce page. */
+	ciphertext_page = alloc_page(GFP_NOFS);
+	if (!ciphertext_page) {
+		/* This is a potential bottleneck, but at least we'll have
+		 * forward progress. */
+		ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
+						 GFP_NOFS);
+		if (WARN_ON_ONCE(!ciphertext_page)) {
+			ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
+							 GFP_NOFS | __GFP_WAIT);
+		}
+		ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
+	} else {
+		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
+	}
+	ctx->bounce_page = ciphertext_page;
+	ctx->control_page = plaintext_page;
+	err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, plaintext_page->index,
+			       plaintext_page, ciphertext_page);
+	if (err) {
+		ext4_release_crypto_ctx(ctx);
+		return ERR_PTR(err);
+	}
+	SetPagePrivate(ciphertext_page);
+	set_page_private(ciphertext_page, (unsigned long)ctx);
+	lock_page(ciphertext_page);
+	return ciphertext_page;
+}
+
+/**
+ * ext4_decrypt() - Decrypts a page in-place
+ * @ctx:  The encryption context.
+ * @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 ext4_decrypt(struct ext4_crypto_ctx *ctx, struct page *page)
+{
+	BUG_ON(!PageLocked(page));
+
+	return ext4_page_crypto(ctx, page->mapping->host,
+				EXT4_DECRYPT, page->index, page, page);
+}
+
+/*
+ * Convenience function which takes care of allocating and
+ * deallocating the encryption context
+ */
+int ext4_decrypt_one(struct inode *inode, struct page *page)
+{
+	int ret;
+
+	struct ext4_crypto_ctx *ctx = ext4_get_crypto_ctx(inode);
+
+	if (!ctx)
+		return -ENOMEM;
+	ret = ext4_decrypt(ctx, page);
+	ext4_release_crypto_ctx(ctx);
+	return ret;
+}
+
+int ext4_encrypted_zeroout(struct inode *inode, struct ext4_extent *ex)
+{
+	struct ext4_crypto_ctx	*ctx;
+	struct page		*ciphertext_page = NULL;
+	struct bio		*bio;
+	ext4_lblk_t		lblk = ex->ee_block;
+	ext4_fsblk_t		pblk = ext4_ext_pblock(ex);
+	unsigned int		len = ext4_ext_get_actual_len(ex);
+	int			err = 0;
+
+	BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);
+
+	ctx = ext4_get_crypto_ctx(inode);
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	ciphertext_page = alloc_page(GFP_NOFS);
+	if (!ciphertext_page) {
+		/* This is a potential bottleneck, but at least we'll have
+		 * forward progress. */
+		ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
+						 GFP_NOFS);
+		if (WARN_ON_ONCE(!ciphertext_page)) {
+			ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
+							 GFP_NOFS | __GFP_WAIT);
+		}
+		ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
+	} else {
+		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
+	}
+	ctx->bounce_page = ciphertext_page;
+
+	while (len--) {
+		err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, lblk,
+				       ZERO_PAGE(0), ciphertext_page);
+		if (err)
+			goto errout;
+
+		bio = bio_alloc(GFP_KERNEL, 1);
+		if (!bio) {
+			err = -ENOMEM;
+			goto errout;
+		}
+		bio->bi_bdev = inode->i_sb->s_bdev;
+		bio->bi_iter.bi_sector = pblk;
+		err = bio_add_page(bio, ciphertext_page,
+				   inode->i_sb->s_blocksize, 0);
+		if (err) {
+			bio_put(bio);
+			goto errout;
+		}
+		err = submit_bio_wait(WRITE, bio);
+		if (err)
+			goto errout;
+	}
+	err = 0;
+errout:
+	ext4_release_crypto_ctx(ctx);
+	return err;
+}
+
+bool ext4_valid_contents_enc_mode(uint32_t mode)
+{
+	return (mode == EXT4_ENCRYPTION_MODE_AES_256_XTS);
+}
+
+/**
+ * ext4_validate_encryption_key_size() - Validate the encryption key size
+ * @mode: The key mode.
+ * @size: The key size to validate.
+ *
+ * Return: The validated key size for @mode. Zero if invalid.
+ */
+uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
+{
+	if (size == ext4_encryption_key_size(mode))
+		return size;
+	return 0;
+}