[PATCH v3 6/7] loopfs: start attaching correct namespace during loop_add()

[Christian Brauner]

Tag loop devices with the namespace the loopfs instance was mounted in.
This has the consequence that loopfs devices carry the correct sysfs
permissions for all their core files. All other devices files will
continue to be correctly owned by the initial namespaces. Here is sample
output:

root@b1:~# mount -t loop loop /mnt
root@b1:~# ln -sf /mnt/loop-control /dev/loop-control
root@b1:~# losetup -f
/dev/loop8
root@b1:~# ln -sf /mnt/loop8 /dev/loop8
root@b1:~# ls -al /sys/class/block/loop8
lrwxrwxrwx 1 root root 0 Apr  7 13:06 /sys/class/block/loop8 -> ../../devices/virtual/block/loop8
root@b1:~# ls -al /sys/class/block/loop8/
total 0
drwxr-xr-x  9 root   root       0 Apr  7 13:06 .
drwxr-xr-x 18 nobody nogroup    0 Apr  7 13:07 ..
-r--r--r--  1 root   root    4096 Apr  7 13:06 alignment_offset
lrwxrwxrwx  1 nobody nogroup    0 Apr  7 13:07 bdi -> ../../bdi/7:8
-r--r--r--  1 root   root    4096 Apr  7 13:06 capability
-r--r--r--  1 root   root    4096 Apr  7 13:06 dev
-r--r--r--  1 root   root    4096 Apr  7 13:06 discard_alignment
-r--r--r--  1 root   root    4096 Apr  7 13:06 events
-r--r--r--  1 root   root    4096 Apr  7 13:06 events_async
-rw-r--r--  1 root   root    4096 Apr  7 13:06 events_poll_msecs
-r--r--r--  1 root   root    4096 Apr  7 13:06 ext_range
-r--r--r--  1 root   root    4096 Apr  7 13:06 hidden
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 holders
-r--r--r--  1 root   root    4096 Apr  7 13:06 inflight
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 integrity
drwxr-xr-x  3 nobody nogroup    0 Apr  7 13:07 mq
drwxr-xr-x  2 root   root       0 Apr  7 13:06 power
drwxr-xr-x  3 nobody nogroup    0 Apr  7 13:07 queue
-r--r--r--  1 root   root    4096 Apr  7 13:06 range
-r--r--r--  1 root   root    4096 Apr  7 13:06 removable
-r--r--r--  1 root   root    4096 Apr  7 13:06 ro
-r--r--r--  1 root   root    4096 Apr  7 13:06 size
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 slaves
-r--r--r--  1 root   root    4096 Apr  7 13:06 stat
lrwxrwxrwx  1 nobody nogroup    0 Apr  7 13:07 subsystem -> ../../../../class/block
drwxr-xr-x  2 root   root       0 Apr  7 13:06 trace
-rw-r--r--  1 root   root    4096 Apr  7 13:06 uevent
root@b1:~#

Cc: Jens Axboe <axboe@xxxxxxxxx>
Reviewed-by: Serge Hallyn <serge@xxxxxxxxxx>
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
/* v2 */
unchanged
- Christian Brauner <christian.brauner@xxxxxxxxxx>:
  - Adapted commit message otherwise unchanged.

/* v3 */
unchanged
---
 drivers/block/loop.c          | 3 +++
 drivers/block/loopfs/loopfs.c | 6 ++++++
 drivers/block/loopfs/loopfs.h | 1 +
 3 files changed, 10 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 40705f5aeabd..a5fe05cba896 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2207,6 +2207,9 @@ static int loop_add(struct loop_device **l, int i, struct inode *inode)
 	disk->private_data	= lo;
 	disk->queue		= lo->lo_queue;
 	sprintf(disk->disk_name, "loop%d", i);
+#ifdef CONFIG_BLK_DEV_LOOPFS
+	loopfs_init(disk, inode);
+#endif
 
 	add_disk(disk);
 
diff --git a/drivers/block/loopfs/loopfs.c b/drivers/block/loopfs/loopfs.c
index 09cd5a919ea2..9fa60c1bcc05 100644
--- a/drivers/block/loopfs/loopfs.c
+++ b/drivers/block/loopfs/loopfs.c
@@ -74,6 +74,12 @@ bool loopfs_wants_remove(const struct loop_device *lo)
 	       (lo->lo_info->lo_flags & LOOPFS_FLAGS_INACTIVE);
 }
 
+void loopfs_init(struct gendisk *disk, struct inode *inode)
+{
+	if (loopfs_i_sb(inode))
+		disk->user_ns = loopfs_i_sb(inode)->s_user_ns;
+}
+
 /**
  * loopfs_add - allocate inode from super block of a loopfs mount
  * @lo:		loop device for which we are creating a new device entry
diff --git a/drivers/block/loopfs/loopfs.h b/drivers/block/loopfs/loopfs.h
index 225d844f5a01..7ca1b872b36e 100644
--- a/drivers/block/loopfs/loopfs.h
+++ b/drivers/block/loopfs/loopfs.h
@@ -31,6 +31,7 @@ extern void loopfs_remove(struct loop_device *lo);
 extern bool loopfs_wants_remove(const struct loop_device *lo);
 extern void loopfs_evict_locked(struct loop_device *lo);
 extern int loopfs_rundown_locked(struct loop_device *lo);
+extern void loopfs_init(struct gendisk *disk, struct inode *inode);
 
 #endif
 
-- 
2.26.2