static int f2fs_write_begin(struct file *file, struct address_space *mapping,
		loff_t pos, unsigned len, unsigned flags,
		struct page **pagep, void **fsdata)
{
	struct inode *inode = mapping->host;
	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
	struct page *page = NULL;
	pgoff_t index = ((unsigned long long) pos) >> PAGE_SHIFT;
	bool need_balance = false;
	block_t blkaddr = NULL_ADDR;
	int err = 0;

	trace_f2fs_write_begin(inode, pos, len, flags);

	/*
	 * We should check this at this moment to avoid deadlock on inode page
	 * and #0 page. The locking rule for inline_data conversion should be:
	 * lock_page(page #0) -> lock_page(inode_page)
	 */
	if (index != 0) {
		err = f2fs_convert_inline_inode(inode);
		if (err)
			goto fail;
	}
repeat:
	page = grab_cache_page_write_begin(mapping, index, flags);
	if (!page) {
		err = -ENOMEM;
		goto fail;
	}

	*pagep = page;

	err = prepare_write_begin(sbi, page, pos, len,
					&blkaddr, &need_balance);
	if (err)
		goto fail;

	if (need_balance && has_not_enough_free_secs(sbi, 0, 0)) {
		unlock_page(page);
		f2fs_balance_fs(sbi, true);
		lock_page(page);
		if (page->mapping != mapping) {
			/* The page got truncated from under us */
			f2fs_put_page(page, 1);
			goto repeat;
		}
	}

	f2fs_wait_on_page_writeback(page, DATA, false);

	/* wait for GCed encrypted page writeback */
	if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
		f2fs_wait_on_encrypted_page_writeback(sbi, blkaddr);

	if (len == PAGE_SIZE || PageUptodate(page))
		return 0;

	if (!(pos & (PAGE_SIZE - 1)) && (pos + len) >= i_size_read(inode)) {
		zero_user_segment(page, len, PAGE_SIZE);
		return 0;
	}

	if (blkaddr == NEW_ADDR) {
		zero_user_segment(page, 0, PAGE_SIZE);
		SetPageUptodate(page);
	} else {
		struct bio *bio;

		bio = f2fs_grab_bio(inode, blkaddr, 1);
		if (IS_ERR(bio)) {
			err = PTR_ERR(bio);
			goto fail;
		}
		bio->bi_opf = REQ_OP_READ;
		if (bio_add_page(bio, page, PAGE_SIZE, 0) < PAGE_SIZE) {
			bio_put(bio);
			err = -EFAULT;
			goto fail;
		}

		__submit_bio(sbi, bio, DATA);

		lock_page(page);
		if (unlikely(page->mapping != mapping)) {
			f2fs_put_page(page, 1);
			goto repeat;
		}
		if (unlikely(!PageUptodate(page))) {
			err = -EIO;
			goto fail;
		}
	}
	return 0;

fail:
	f2fs_put_page(page, 1);
	f2fs_write_failed(mapping, pos + len);
	return err;
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.