// SPDX-License-Identifier: GPL-2.0
/*
 * Utility functions for file contents encryption/decryption on
 * block device-based filesystems.
 *
 * Copyright (C) 2015, Google, Inc.
 * Copyright (C) 2015, Motorola Mobility
 */

#include <linux/bio.h>
#include <linux/export.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/pagemap.h>

#include "fscrypt_private.h"

/**
 * fscrypt_decrypt_bio() - decrypt the contents of a bio
 * @bio: the bio to decrypt
 *
 * Decrypt the contents of a "read" bio following successful completion of the
 * underlying disk read.  The bio must be reading a whole number of blocks of an
 * encrypted file directly into the page cache.  If the bio is reading the
 * ciphertext into bounce pages instead of the page cache (for example, because
 * the file is also compressed, so decompression is required after decryption),
 * then this function isn't applicable.  This function may sleep, so it must be
 * called from a workqueue rather than from the bio's bi_end_io callback.
 *
 * Return: %true on success; %false on failure.  On failure, bio->bi_status is
 *         also set to an error status.
 */
bool fscrypt_decrypt_bio(struct bio *bio)
{
        struct folio_iter fi;

        bio_for_each_folio_all(fi, bio) {
                int err = fscrypt_decrypt_pagecache_blocks(fi.folio, fi.length,
                                                           fi.offset);

                if (err) {
                        bio->bi_status = errno_to_blk_status(err);
                        return false;
                }
        }
        return true;
}
EXPORT_SYMBOL(fscrypt_decrypt_bio);

struct fscrypt_zero_done {
        atomic_t                pending;
        blk_status_t            status;
        struct completion       done;
};

static void fscrypt_zeroout_range_done(struct fscrypt_zero_done *done)
{
        if (atomic_dec_and_test(&done->pending))
                complete(&done->done);
}

static void fscrypt_zeroout_range_end_io(struct bio *bio)
{
        struct fscrypt_zero_done *done = bio->bi_private;

        if (bio->bi_status)
                cmpxchg(&done->status, 0, bio->bi_status);
        fscrypt_zeroout_range_done(done);
        bio_put(bio);
}

static int fscrypt_zeroout_range_inline_crypt(const struct inode *inode,
                                              pgoff_t lblk, sector_t sector,
                                              unsigned int len)
{
        const unsigned int blockbits = inode->i_blkbits;
        const unsigned int blocks_per_page = 1 << (PAGE_SHIFT - blockbits);
        struct fscrypt_zero_done done = {
                .pending        = ATOMIC_INIT(1),
                .done           = COMPLETION_INITIALIZER_ONSTACK(done.done),
        };

        while (len) {
                struct bio *bio;
                unsigned int n;

                bio = bio_alloc(inode->i_sb->s_bdev, BIO_MAX_VECS, REQ_OP_WRITE,
                                GFP_NOFS);
                bio->bi_iter.bi_sector = sector;
                bio->bi_private = &done;
                bio->bi_end_io = fscrypt_zeroout_range_end_io;
                fscrypt_set_bio_crypt_ctx(bio, inode, lblk, GFP_NOFS);

                for (n = 0; n < BIO_MAX_VECS; n++) {
                        unsigned int blocks_this_page =
                                min(len, blocks_per_page);
                        unsigned int bytes_this_page = blocks_this_page << blockbits;

                        __bio_add_page(bio, ZERO_PAGE(0), bytes_this_page, 0);
                        len -= blocks_this_page;
                        lblk += blocks_this_page;
                        sector += (bytes_this_page >> SECTOR_SHIFT);
                        if (!len || !fscrypt_mergeable_bio(bio, inode, lblk))
                                break;
                }

                atomic_inc(&done.pending);
                blk_crypto_submit_bio(bio);
        }

        fscrypt_zeroout_range_done(&done);

        wait_for_completion(&done.done);
        return blk_status_to_errno(done.status);
}

/**
 * fscrypt_zeroout_range() - zero out a range of blocks in an encrypted file
 * @inode: the file's inode
 * @lblk: the first file logical block to zero out
 * @pblk: the first filesystem physical block to zero out
 * @len: number of blocks to zero out
 *
 * Zero out filesystem blocks in an encrypted regular file on-disk, i.e. write
 * ciphertext blocks which decrypt to the all-zeroes block.  The blocks must be
 * both logically and physically contiguous.  It's also assumed that the
 * filesystem only uses a single block device, ->s_bdev.
 *
 * Note that since each block uses a different IV, this involves writing a
 * different ciphertext to each block; we can't simply reuse the same one.
 *
 * Return: 0 on success; -errno on failure.
 */
int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
                          sector_t pblk, unsigned int len)
{
        const struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(inode);
        const unsigned int du_bits = ci->ci_data_unit_bits;
        const unsigned int du_size = 1U << du_bits;
        const unsigned int du_per_page_bits = PAGE_SHIFT - du_bits;
        const unsigned int du_per_page = 1U << du_per_page_bits;
        u64 du_index = (u64)lblk << (inode->i_blkbits - du_bits);
        u64 du_remaining = (u64)len << (inode->i_blkbits - du_bits);
        sector_t sector = pblk << (inode->i_blkbits - SECTOR_SHIFT);
        struct page *pages[16]; /* write up to 16 pages at a time */
        unsigned int nr_pages;
        unsigned int i;
        unsigned int offset;
        struct bio *bio;
        int ret, err;

        if (len == 0)
                return 0;

        if (fscrypt_inode_uses_inline_crypto(inode))
                return fscrypt_zeroout_range_inline_crypt(inode, lblk, sector,
                                                          len);

        BUILD_BUG_ON(ARRAY_SIZE(pages) > BIO_MAX_VECS);
        nr_pages = min_t(u64, ARRAY_SIZE(pages),
                         (du_remaining + du_per_page - 1) >> du_per_page_bits);

        /*
         * We need at least one page for ciphertext.  Allocate the first one
         * from a mempool, with __GFP_DIRECT_RECLAIM set so that it can't fail.
         *
         * Any additional page allocations are allowed to fail, as they only
         * help performance, and waiting on the mempool for them could deadlock.
         */
        for (i = 0; i < nr_pages; i++) {
                pages[i] = fscrypt_alloc_bounce_page(i == 0 ? GFP_NOFS :
                                                     GFP_NOWAIT);
                if (!pages[i])
                        break;
        }
        nr_pages = i;
        if (WARN_ON_ONCE(nr_pages <= 0))
                return -EINVAL;

        /* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
        bio = bio_alloc(inode->i_sb->s_bdev, nr_pages, REQ_OP_WRITE, GFP_NOFS);

        do {
                bio->bi_iter.bi_sector = sector;

                i = 0;
                offset = 0;
                do {
                        err = fscrypt_crypt_data_unit(ci, FS_ENCRYPT, du_index,
                                                      ZERO_PAGE(0), pages[i],
                                                      du_size, offset);
                        if (err)
                                goto out;
                        du_index++;
                        sector += 1U << (du_bits - SECTOR_SHIFT);
                        du_remaining--;
                        offset += du_size;
                        if (offset == PAGE_SIZE || du_remaining == 0) {
                                ret = bio_add_page(bio, pages[i++], offset, 0);
                                if (WARN_ON_ONCE(ret != offset)) {
                                        err = -EIO;
                                        goto out;
                                }
                                offset = 0;
                        }
                } while (i != nr_pages && du_remaining != 0);

                err = submit_bio_wait(bio);
                if (err)
                        goto out;
                bio_reset(bio, inode->i_sb->s_bdev, REQ_OP_WRITE);
        } while (du_remaining != 0);
        err = 0;
out:
        bio_put(bio);
        for (i = 0; i < nr_pages; i++)
                fscrypt_free_bounce_page(pages[i]);
        return err;
}
EXPORT_SYMBOL(fscrypt_zeroout_range);