rbd: disallow read-write partitions on images mapped read-only

If an image is mapped read-only, don't allow setting its partition(s)
to read-write via BLKROSET: with the previous patch all writes to such
images are failed anyway.

If an image is mapped read-write, its partition(s) can be set to
read-only (and back to read-write) as before.  Note that at the rbd
level the image will remain writeable: anything sent down by the block
layer will be executed, including any write from internal kernel users.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 02cd2a7..978e4d8 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -706,9 +706,16 @@ static int rbd_ioctl_set_ro(struct rbd_device *rbd_dev, unsigned long arg)
        if (get_user(ro, (int __user *)arg))
                return -EFAULT;
 
-       /* Snapshots can't be marked read-write */
-       if (rbd_is_snap(rbd_dev) && !ro)
-               return -EROFS;
+       /*
+        * Both images mapped read-only and snapshots can't be marked
+        * read-write.
+        */
+       if (!ro) {
+               if (rbd_is_ro(rbd_dev))
+                       return -EROFS;
+
+               rbd_assert(!rbd_is_snap(rbd_dev));
+       }
 
        /* Let blkdev_roset() handle it */
        return -ENOTTY;