/*
 * 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/skcipher.h>
#include <keys/user-type.h>
#include <keys/encrypted-type.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 <linux/namei.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);

static struct kmem_cache *ext4_crypto_ctx_cachep;
struct kmem_cache *ext4_crypt_info_cachep;

/**
 * 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->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page)
                mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
        ctx->w.bounce_page = NULL;
        ctx->w.control_page = NULL;
        if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
                kmem_cache_free(ext4_crypto_ctx_cachep, 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_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,
                                            gfp_t gfp_flags)
{
        struct ext4_crypto_ctx *ctx = NULL;
        int res = 0;
        unsigned long flags;
        struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;

        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(&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 = kmem_cache_zalloc(ext4_crypto_ctx_cachep, gfp_flags);
                if (!ctx) {
                        res = -ENOMEM;
                        goto out;
                }
                ctx->flags |= EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
        } else {
                ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
        }
        ctx->flags &= ~EXT4_WRITE_PATH_FL;

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)
                kmem_cache_free(ext4_crypto_ctx_cachep, 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;
        if (ext4_crypto_ctx_cachep)
                kmem_cache_destroy(ext4_crypto_ctx_cachep);
        ext4_crypto_ctx_cachep = NULL;
        if (ext4_crypt_info_cachep)
                kmem_cache_destroy(ext4_crypt_info_cachep);
        ext4_crypt_info_cachep = 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 = -ENOMEM;

        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)
                goto fail;

        ext4_crypto_ctx_cachep = KMEM_CACHE(ext4_crypto_ctx,
                                            SLAB_RECLAIM_ACCOUNT);
        if (!ext4_crypto_ctx_cachep)
                goto fail;

        ext4_crypt_info_cachep = KMEM_CACHE(ext4_crypt_info,
                                            SLAB_RECLAIM_ACCOUNT);
        if (!ext4_crypt_info_cachep)
                goto fail;

        for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
                struct ext4_crypto_ctx *ctx;

                ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, GFP_NOFS);
                if (!ctx) {
                        res = -ENOMEM;
                        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 inode *inode,
                            ext4_direction_t rw,
                            pgoff_t index,
                            struct page *src_page,
                            struct page *dest_page,
                            gfp_t gfp_flags)

{
        u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
        struct skcipher_request *req = NULL;
        DECLARE_EXT4_COMPLETION_RESULT(ecr);
        struct scatterlist dst, src;
        struct ext4_crypt_info *ci = EXT4_I(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,
                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_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 == EXT4_DECRYPT)
                res = crypto_skcipher_decrypt(req);
        else
                res = crypto_skcipher_encrypt(req);
        if (res == -EINPROGRESS || res == -EBUSY) {
                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 ext4_crypto_ctx *ctx,
                                      gfp_t gfp_flags)
{
        ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, gfp_flags);
        if (ctx->w.bounce_page == NULL)
                return ERR_PTR(-ENOMEM);
        ctx->flags |= EXT4_WRITE_PATH_FL;
        return ctx->w.bounce_page;
}

/**
 * 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,
                          gfp_t gfp_flags)
{
        struct ext4_crypto_ctx *ctx;
        struct page *ciphertext_page = NULL;
        int err;

        BUG_ON(!PageLocked(plaintext_page));

        ctx = ext4_get_crypto_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 = ext4_page_crypto(inode, EXT4_ENCRYPT, plaintext_page->index,
                               plaintext_page, ciphertext_page, gfp_flags);
        if (err) {
                ciphertext_page = ERR_PTR(err);
        errout:
                ext4_release_crypto_ctx(ctx);
                return ciphertext_page;
        }
        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 page *page)
{
        BUG_ON(!PageLocked(page));

        return ext4_page_crypto(page->mapping->host, EXT4_DECRYPT,
                                page->index, page, page, GFP_NOFS);
}

int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
                           ext4_fsblk_t pblk, ext4_lblk_t len)
{
        struct ext4_crypto_ctx  *ctx;
        struct page             *ciphertext_page = NULL;
        struct bio              *bio;
        int                     ret, err = 0;

#if 0
        ext4_msg(inode->i_sb, KERN_CRIT,
                 "ext4_encrypted_zeroout ino %lu lblk %u len %u",
                 (unsigned long) inode->i_ino, lblk, len);
#endif

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

        ctx = ext4_get_crypto_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 = ext4_page_crypto(inode, EXT4_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! */
                        ext4_msg(inode->i_sb, KERN_ERR,
                                 "bio_add_page failed: %d", ret);
                        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:
        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;
}

/*
 * 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 ext4_d_revalidate(struct dentry *dentry, unsigned int flags)
{
        struct dentry *dir;
        struct ext4_crypt_info *ci;
        int dir_has_key, cached_with_key;

        if (flags & LOOKUP_RCU)
                return -ECHILD;

        dir = dget_parent(dentry);
        if (!ext4_encrypted_inode(d_inode(dir))) {
                dput(dir);
                return 0;
        }
        ci = EXT4_I(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 */
        cached_with_key = dentry->d_fsdata != NULL;
        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)) {
#if 0                           /* Revalidation debug */
                char buf[80];
                char *cp = simple_dname(dentry, buf, sizeof(buf));

                if (IS_ERR(cp))
                        cp = (char *) "???";
                pr_err("revalidate: %s %p %d %d %d\n", cp, dentry->d_fsdata,
                       cached_with_key, d_is_negative(dentry),
                       dir_has_key);
#endif
                return 0;
        }
        return 1;
}

const struct dentry_operations ext4_encrypted_d_ops = {
        .d_revalidate = ext4_d_revalidate,
};