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Date:   Wed,  8 Apr 2020 17:21:51 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     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
Cc:     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>,
        Christian Brauner <christian.brauner@...ntu.com>,
        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>,
        St├ęphane Graber <stgraber@...ntu.com>,
        linux-doc@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH 8/8] loopfs: only show devices in their correct instance

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>
---
 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

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