Re: [PATCH][V3] overlayfs: During copy up, first copy up data and then xattrs

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, Jan 11, 2019 at 7:37 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> If a file with capability set (and hence security.capability xattr) is
> written kernel clears security.capability xattr. For overlay, during file
> copy up if xattrs are copied up first and then data is, copied up. This
> means data copy up will result in clearing of security.capability xattr
> file on lower has. And this can result into surprises. If
> a lower file has CAP_SETUID, then it should not be cleared over
> copy up (if nothing was actually written to file).
>
> This also creates problems with chown logic where it first copies up file
> and then tries to clear setuid bit. But by that time security.capability
> xattr is already gone (due to data copy up), and caller gets -ENODATA.
> This has been reported by Giuseppe here.
>
> https://github.com/containers/libpod/issues/2015#issuecomment-447824842
>
> Fix this by copying up data first and then metadta. This is a regression
> which has been introduced by my commit as part of metadata only copy up
> patches.
>
> TODO: There will be some corner cases where a file is copied up metadata
>       only and later data copy up happens and that will clear
>       security.capability xattr. Something needs to be done about that too.
>
> Fixes: bd64e57586d3 ("ovl: During copy up, first copy up metadata and then data")
> Cc: <stable@vger.kernel.org> # v4.19+
> Reported-by: Giuseppe Scrivano <gscrivan@redhat.com>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Thanks, applied.

Miklos