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From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Jens Axboe <axboe@kernel.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-api@vger.kernel.org
Cc:     Jonathan Corbet <corbet@lwn.net>, Serge Hallyn <serge@hallyn.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>, Tejun Heo <tj@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Saravana Kannan <saravanak@google.com>,
        Jan Kara <jack@suse.cz>, David Howells <dhowells@redhat.com>,
        Seth Forshee <seth.forshee@canonical.com>,
        David Rheinsberg <david.rheinsberg@gmail.com>,
        Tom Gundersen <teg@jklm.no>,
        Christian Kellner <ckellner@redhat.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        =?UTF-8?q?St=C3=A9phane=20Graber?= <stgraber@ubuntu.com>,
        linux-doc@vger.kernel.org, netdev@vger.kernel.org
Subject: [PATCH 8/8] loopfs: only show devices in their correct instance
Date:   Wed,  8 Apr 2020 17:21:51 +0200
Message-Id: <20200408152151.5780-9-christian.brauner@ubuntu.com>
In-Reply-To: <20200408152151.5780-1-christian.brauner@ubuntu.com>
References: <20200408152151.5780-1-christian.brauner@ubuntu.com>
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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@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 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 7a14fd3e4329..df75ca4ac040 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2155,8 +2155,10 @@ 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 fa04dfd22bbc..9fa438e3e4ca 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -525,6 +525,8 @@ 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
@@ -625,6 +627,7 @@ 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)
-- 
2.26.0