On 4/27/21 6:05 AM, Junxiao Bi wrote:
> When fallocate/truncate extend inode size, if the original isize is in
> the middle of last cluster, then the part from isize to the end of the
> cluster needs to be zeroed with buffer write, at that time isize is not
> yet updated to match the new size, if writeback is kicked in, it will
> invoke ocfs2_writepage()->block_write_full_page() where the pages out
> of inode size will be dropped. That will cause file corruption.
>
> Running the following command with qemu-image 4.2.1 can get a corrupted
> coverted image file easily.
>
> qemu-img convert -p -t none -T none -f qcow2 $qcow_image \
> -O qcow2 -o compat=1.1 $qcow_image.conv
>
> Cc: <[email protected]>
> Signed-off-by: Junxiao Bi <[email protected]>
Reviewed-by: Joseph Qi <[email protected]>
> ---
> fs/ocfs2/aops.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index ad20403b383f..7a3e3d59f6a9 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -402,11 +402,28 @@ static void ocfs2_readahead(struct readahead_control
> *rac)
> */
> static int ocfs2_writepage(struct page *page, struct writeback_control *wbc)
> {
> + struct inode * const inode = page->mapping->host;
> + loff_t i_size = i_size_read(inode);
> + const pgoff_t end_index = i_size >> PAGE_SHIFT;
> + unsigned int offset;
> +
> trace_ocfs2_writepage(
> (unsigned long long)OCFS2_I(page->mapping->host)->ip_blkno,
> page->index);
>
> - return block_write_full_page(page, ocfs2_get_block, wbc);
> + /*
> + * The page straddles i_size. It must be zeroed out on each and every
> + * writepage invocation because it may be mmapped. "A file is mapped
> + * in multiples of the page size. For a file that is not a multiple of
> + * the page size, the remaining memory is zeroed when mapped, and
> + * writes to that region are not written out to the file."
> + */
> + offset = i_size & (PAGE_SIZE-1);
> + if (page->index == end_index && offset)
> + zero_user_segment(page, offset, PAGE_SIZE);
> +
> + return __block_write_full_page_eof(inode, page, ocfs2_get_block, wbc,
> + end_buffer_async_write, true);
> }
>
> /* Taken from ext3. We don't necessarily need the full blown
>
