[Help] Problem when using overlayfs with LoadPin

[Help] Problem when using overlayfs with LoadPin

[Anders Dellien]

Hi all,

I have previously successfully used LoadPin [https://www.kernel.org/doc/html/latest/admin-guide/LSM/LoadPin.html]
together with overlayfs, however commit a6518f "vfs: don't open real" introduces a regression.

(from loadpin.c):

        /* file_dentry sees through overlays */
        load_root = file_dentry(file)->d_sb;  (here, load_root->s_bdev is NULL and not the actual block device from the lower layer)

Questions:
* Maybe this is expected behavior and I am doing something wrong? Maybe there is some build- or mount option that
could fix the problem?
* If this really is a bug in overlayfs then I would be happy to try to fix it - however as I am not familiar with the code
I would very much appreciate if someone more knowledgeable could point me in the right direction.

Thanks,
Anders

Re: [Help] Problem when using overlayfs with LoadPin

[Miklos Szeredi]

On Fri, Nov 8, 2019 at 9:42 AM Anders Dellien <anders.dellien@axis.com> wrote:
>
> Hi all,
>
> I have previously successfully used LoadPin [https://www.kernel.org/doc/html/latest/admin-guide/LSM/LoadPin.html]
> together with overlayfs, however commit a6518f "vfs: don't open real" introduces a regression.
>
> (from loadpin.c):
>
>         /* file_dentry sees through overlays */
>         load_root = file_dentry(file)->d_sb;  (here, load_root->s_bdev is NULL and not the actual block device from the lower layer)

Umm, where does the above line come from?

Mainline looks like this:

    load_root = file->f_path.mnt->mnt_sb;

What is the expected behavior?   Should loadpin see through overlayfs or not?

Thanks.
Miklos