f2fs: fix a dead loop in f2fs_fiemap()

A dead loop can be triggered in f2fs_fiemap() using the test case
as below:

	...
	fd = open();
	fallocate(fd, 0, 0, 4294967296);
	ioctl(fd, FS_IOC_FIEMAP, fiemap_buf);
	...

It's caused by an overflow in __get_data_block():
	...
	bh->b_size = map.m_len << inode->i_blkbits;
	...
map.m_len is an unsigned int, and bh->b_size is a size_t which is 64 bits
on 64 bits archtecture, type conversion from an unsigned int to a size_t
will result in an overflow.

In the above-mentioned case, bh->b_size will be zero, and f2fs_fiemap()
will call get_data_block() at block 0 again an again.

Fix this by adding a force conversion before left shift.

Signed-off-by: Wei Fang <fangwei1@huawei.com>
Acked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
struct page *get_read_data_page(struct inode *inode, pgoff_t index,
						int op_flags, bool for_write)
{
	struct address_space *mapping = inode->i_mapping;
	struct dnode_of_data dn;
	struct page *page;
	struct extent_info ei;
	int err;
	struct f2fs_io_info fio = {
		.sbi = F2FS_I_SB(inode),
		.type = DATA,
		.op = REQ_OP_READ,
		.op_flags = op_flags,
		.encrypted_page = NULL,
	};

	if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
		return read_mapping_page(mapping, index, NULL);

	page = f2fs_grab_cache_page(mapping, index, for_write);
	if (!page)
		return ERR_PTR(-ENOMEM);

	if (f2fs_lookup_extent_cache(inode, index, &ei)) {
		dn.data_blkaddr = ei.blk + index - ei.fofs;
		goto got_it;
	}

	set_new_dnode(&dn, inode, NULL, NULL, 0);
	err = get_dnode_of_data(&dn, index, LOOKUP_NODE);
	if (err)
		goto put_err;
	f2fs_put_dnode(&dn);

	if (unlikely(dn.data_blkaddr == NULL_ADDR)) {
		err = -ENOENT;
		goto put_err;
	}
got_it:
	if (PageUptodate(page)) {
		unlock_page(page);
		return page;
	}

	/*
	 * A new dentry page is allocated but not able to be written, since its
	 * new inode page couldn't be allocated due to -ENOSPC.
	 * In such the case, its blkaddr can be remained as NEW_ADDR.
	 * see, f2fs_add_link -> get_new_data_page -> init_inode_metadata.
	 */
	if (dn.data_blkaddr == NEW_ADDR) {
		zero_user_segment(page, 0, PAGE_SIZE);
		if (!PageUptodate(page))
			SetPageUptodate(page);
		unlock_page(page);
		return page;
	}

	fio.new_blkaddr = fio.old_blkaddr = dn.data_blkaddr;
	fio.page = page;
	err = f2fs_submit_page_bio(&fio);
	if (err)
		goto put_err;
	return page;

put_err:
	f2fs_put_page(page, 1);
	return ERR_PTR(err);
}

struct page *get_read_data_page(struct inode *inode, pgoff_t index,
						int op_flags, bool for_write)
{
	struct address_space *mapping = inode->i_mapping;
	struct dnode_of_data dn;
	struct page *page;
	struct extent_info ei;
	int err;
	struct f2fs_io_info fio = {
		.sbi = F2FS_I_SB(inode),
		.type = DATA,
		.op = REQ_OP_READ,
		.op_flags = op_flags,
		.encrypted_page = NULL,
	};

	if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
		return read_mapping_page(mapping, index, NULL);

	page = f2fs_grab_cache_page(mapping, index, for_write);
	if (!page)
		return ERR_PTR(-ENOMEM);

	if (f2fs_lookup_extent_cache(inode, index, &ei)) {
		dn.data_blkaddr = ei.blk + index - ei.fofs;
		goto got_it;
	}

	set_new_dnode(&dn, inode, NULL, NULL, 0);
	err = get_dnode_of_data(&dn, index, LOOKUP_NODE);
	if (err)
		goto put_err;
	f2fs_put_dnode(&dn);

	if (unlikely(dn.data_blkaddr == NULL_ADDR)) {
		err = -ENOENT;
		goto put_err;
	}
got_it:
	if (PageUptodate(page)) {
		unlock_page(page);
		return page;
	}

	/*
	 * A new dentry page is allocated but not able to be written, since its
	 * new inode page couldn't be allocated due to -ENOSPC.
	 * In such the case, its blkaddr can be remained as NEW_ADDR.
	 * see, f2fs_add_link -> get_new_data_page -> init_inode_metadata.
	 */
	if (dn.data_blkaddr == NEW_ADDR) {
		zero_user_segment(page, 0, PAGE_SIZE);
		if (!PageUptodate(page))
			SetPageUptodate(page);
		unlock_page(page);
		return page;
	}

	fio.new_blkaddr = fio.old_blkaddr = dn.data_blkaddr;
	fio.page = page;
	err = f2fs_submit_page_bio(&fio);
	if (err)
		goto put_err;
	return page;

put_err:
	f2fs_put_page(page, 1);
	return ERR_PTR(err);
}
