The BDRV_O_ALLOW_RDWR flag allows / prohibits the changing of
the BDS 'read_only' state, but there are a few places where it
is ignored.  In the bdrv_set_read_only() helper, make sure to
honor the flag.

Signed-off-by: Jeff Cody <jcody@redhat.com>
---
 block.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block.c b/block.c
index c9eb613..68a18b0 100644
--- a/block.c
+++ b/block.c
@@ -201,6 +201,13 @@ int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
         return -EINVAL;
     }
 
+    /* Do not clear read_only if it is prohibited */
+    if (!read_only && !(bs->open_flags & BDRV_O_ALLOW_RDWR)) {
+        error_setg(errp, "Node '%s' is read only",
+                   bdrv_get_device_or_node_name(bs));
+        return -EPERM;
+    }
+
     bs->read_only = read_only;
     return 0;
 }
-- 
2.9.3