[PATCH 6.5.y] erofs: ensure that the post-EOF tails are all zeroed

[Greg Kroah-Hartman]

On Thu, Aug 31, 2023 at 07:29:53PM +0800, Gao Xiang wrote:
> commit e4c1cf523d820730a86cae2c6d55924833b6f7ac upstream.
> 
> This was accidentally fixed up in commit e4c1cf523d82 but we can't
> take the full change due to other dependancy issues, so here is just
> the actual bugfix that is needed.
> 
> [Background]
> 
> keltargw reported an issue [1] that with mmaped I/Os, sometimes the
> tail of the last page (after file ends) is not filled with zeroes.
> 
> The root cause is that such tail page could be wrongly selected for
> inplace I/Os so the zeroed part will then be filled with compressed
> data instead of zeroes.
> 
> A simple fix is to avoid doing inplace I/Os for such tail parts,
> actually that was already fixed upstream in commit e4c1cf523d82
> ("erofs: tidy up z_erofs_do_read_page()") by accident.
> 
> [1] https://lore.kernel.org/r/3ad8b469-25db-a297-21f9-75db2d6ad224@linux.alibaba.com
> 
> Reported-by: keltargw <keltar.gw at gmail.com>
> Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> ---
>  fs/erofs/zdata.c | 2 ++
>  1 file changed, 2 insertions(+)

All now queued up, thanks.

greg k-h