linux-kernel - Re: d_path() and overlay fs

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Date:	Fri, 20 Mar 2015 09:41:25 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Karel Zak <kzak@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: d_path() and overlay fs

On Fri, Mar 20, 2015 at 9:29 AM, Karel Zak <kzak@...hat.com> wrote:
>
>  Hi,
>
>  kernel-4.0.0-0.rc4.git1.3.fc23 (I have nothing more recent right now,
>  sorry it the problem is already fixed).

That equates to Linux v4.0-rc4-88-g7b09ac704bac upstream.

Fedora has Linux v4.0-rc4-199-gb314acaccd7e queued to build today,
which does include an overlayfs fix pull but I have no idea if it
solves the issue.

josh

>
>  It seems like d_path() kernel function returns nonsenses for overlay fs.
>
>  Example:
>
>    # mount -t overlay overlay -olowerdir=/mnt/low,upperdir=/mnt/up/data,workdir=/mnt/up/work /mnt/merged
>    # dd if=/dev/zero of=/mnt/merged/image count=1 bs=1MiB
>
>    # losetup -f /mnt/merged/image
>
>    # cat /sys/block/loop0/loop/backing_file
>    /image
>
>
>  ...should be /mnt/merged/image.
>
>  drivers/block/loop.c: loop_attr_backing_file_show() uses d_path()
>
>  It seems like serious problem because kernel uses d_path() (and
>  friends) on many places to generate path strings for userspace in
>  /proc and /sys and people already use overlay fs in containers.
>
>  Another example:
>
>    # cat /proc/swaps
>    Filename               Type        Size    Used    Priority
>    /dev/sda6              partition   8191996 258308  -1
>    /image                 file        1020    0       -2
>
>
>     Karel
>
> --
>  Karel Zak  <kzak@...hat.com>
>  http://karelzak.blogspot.com
> --
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