/*
 * 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/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>
#include <linux/ecryptfs.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 skcipher_request *req = NULL;
        DECLARE_FS_COMPLETION_RESULT(ecr);
        struct scatterlist dst, src;
        struct fscrypt_info *ci = inode->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;

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

        skcipher_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_SIZE, 0);
        sg_init_table(&src, 1);
        sg_set_page(&src, src_page, PAGE_SIZE, 0);
        skcipher_request_set_crypt(req, &src, &dst, PAGE_SIZE,
                                        xts_tweak);
        if (rw == FS_DECRYPT)
                res = crypto_skcipher_decrypt(req);
        else
                res = crypto_skcipher_encrypt(req);
        if (res == -EINPROGRESS || res == -EBUSY) {
                BUG_ON(req->base.data != &ecr);
                wait_for_completion(&ecr.completion);
                res = ecr.res;
        }
        skcipher_request_free(req);
        if (res) {
                printk_ratelimited(KERN_ERR
                        "%s: crypto_skcipher_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_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_iter.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);
                if ((err == 0) && bio->bi_error)
                        err = -EIO;
                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 && d_is_negative(dentry)) ||
                        (!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");