linux-kernel - Re: [PATCH v2 7/7] loopfs: only show devices in their correct instance

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Message-ID: <20200423013754.GC2982@mail.hallyn.com>
Date:   Wed, 22 Apr 2020 20:37:54 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-api@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Serge Hallyn <serge@...lyn.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, Tejun Heo <tj@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saravana Kannan <saravanak@...gle.com>,
        Jan Kara <jack@...e.cz>, David Howells <dhowells@...hat.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        David Rheinsberg <david.rheinsberg@...il.com>,
        Tom Gundersen <teg@...m.no>,
        Christian Kellner <ckellner@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        linux-doc@...r.kernel.org, netdev@...r.kernel.org,
        Steve Barber <smbarber@...gle.com>,
        Dylan Reid <dgreid@...gle.com>,
        Filipe Brandenburger <filbranden@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Benjamin Elder <bentheelder@...gle.com>,
        Akihiro Suda <suda.kyoto@...il.com>
Subject: Re: [PATCH v2 7/7] loopfs: only show devices in their correct
 instance

On Wed, Apr 22, 2020 at 04:54:37PM +0200, Christian Brauner wrote:
> Since loopfs devices belong to a loopfs instance they have no business
> polluting the host's devtmpfs mount and should not propagate out of the
> namespace they belong to.
> 
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>

Reviewed-by: Serge Hallyn <serge@...lyn.com>

> ---
> /* v2 */
> unchanged
> ---
>  drivers/base/devtmpfs.c | 4 ++--
>  drivers/block/loop.c    | 4 +++-
>  include/linux/device.h  | 3 +++
>  3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index c9017e0584c0..77371ceb88fa 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -111,7 +111,7 @@ int devtmpfs_create_node(struct device *dev)
>  	const char *tmp = NULL;
>  	struct req req;
>  
> -	if (!thread)
> +	if (!thread || dev->no_devnode)
>  		return 0;
>  
>  	req.mode = 0;
> @@ -138,7 +138,7 @@ int devtmpfs_delete_node(struct device *dev)
>  	const char *tmp = NULL;
>  	struct req req;
>  
> -	if (!thread)
> +	if (!thread || dev->no_devnode)
>  		return 0;
>  
>  	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 2dc53bad4b48..5548151b9f11 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2213,8 +2213,10 @@ static int loop_add(struct loop_device **l, int i, struct inode *inode)
>  	disk->queue		= lo->lo_queue;
>  	sprintf(disk->disk_name, "loop%d", i);
>  #ifdef CONFIG_BLK_DEV_LOOPFS
> -	if (loopfs_i_sb(inode))
> +	if (loopfs_i_sb(inode)) {
>  		disk->user_ns = loopfs_i_sb(inode)->s_user_ns;
> +		disk_to_dev(disk)->no_devnode = true;
> +	}
>  #endif
>  
>  	add_disk(disk);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index ac8e37cd716a..c69ef1c5a0ef 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -523,6 +523,8 @@ struct dev_links_info {
>   *		  sync_state() callback.
>   * @dma_coherent: this particular device is dma coherent, even if the
>   *		architecture supports non-coherent devices.
> + * @no_devnode: whether device nodes associated with this device are kept out
> + *		of devtmpfs (e.g. due to separate filesystem)
>   *
>   * At the lowest level, every device in a Linux system is represented by an
>   * instance of struct device. The device structure contains the information
> @@ -622,6 +624,7 @@ struct device {
>      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
>  	bool			dma_coherent:1;
>  #endif
> +	bool			no_devnode:1;
>  };
>  
>  static inline struct device *kobj_to_dev(struct kobject *kobj)
> -- 
> 2.26.1