Fix a bug where read-only volumes were recognized as read-write.

chromeos/disks/disk_mount_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chromeos/disks/disk_mount_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
@@ skipping 342 matching lines @@
          mount_info.mount_condition) &&
         mount_info.mount_type == MOUNT_TYPE_DEVICE &&
         !mount_info.source_path.empty() &&
         !mount_info.mount_path.empty()) {
       DiskMap::iterator iter = disks_.find(mount_info.source_path);
       if (iter != disks_.end()) {  // disk might have been removed by now?
         Disk* disk = iter->second;
         DCHECK(disk);
         // The is_read_only field in *disk may be incorrect when this is called
         // from CrosDisksClientImpl::OnMountCompleted.
-        // Overwrite based on the access mode option that was passed when
-        // issuing
-        // mount command to the same mount path last time.
+        // The disk should be treated as read-only when:
+        //  - the read-only option was passed when issuing mount command
+        //  - or the device hardware is read-only.
         // |source_path| should be same as |disk->device_path| because
         // |VolumeManager::OnDiskEvent()| passes the latter to cros-disks as a
         // source path when mounting a device.
         AccessModeMap::iterator it = access_modes_.find(entry.source_path());
-        if (it != access_modes_.end()) {
-          disk->set_read_only(it->second ==
-                              chromeos::MOUNT_ACCESS_MODE_READ_ONLY);
+        if (it != access_modes_.end() &&
+            it->second == chromeos::MOUNT_ACCESS_MODE_READ_ONLY) {
+          disk->set_read_only(true);
         }
         disk->set_mount_path(mount_info.mount_path);
       }
     }
     // Observers may read the values of disks_. So notify them after tweaking
     // values of disks_.
     NotifyMountStatusUpdate(MOUNTING, entry.error_code(), mount_info);
   }
 
   // Callback for UnmountPath.
@@ skipping 412 matching lines @@
   VLOG(1) << "DiskMountManager Shutdown completed";
 }
 
 // static
 DiskMountManager* DiskMountManager::GetInstance() {
   return g_disk_mount_manager;
 }
 
 }  // namespace disks
 }  // namespace chromeos