misc/172334: unionfs permits recursive union mounts; causes panic quickly

[Garrett Cooper]

>Number:         172334
>Category:       misc
>Synopsis:       unionfs permits recursive union mounts; causes panic quickly
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Oct 04 19:00:21 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Garrett Cooper
>Release:        9.0-RELEASE
>Organization:
EMC Isilon
>Environment:
9.0-RELEASE amd64 install media
>Description:
I accidentally got my invocation backwards, was impatient and tried the opposite form and it blew up looking in the VOP code when I did the following:

1. Boot 9.0-RELEASE as a LiveCD.
2. Execute the following commands:
   mkdir /tmp/etc
   mount_unionfs /tmp/etc /etc
   mount_unionfs /etc /tmp/etc
3. Accessing either /etc or /tmp/etc after that should result in a panic.
>How-To-Repeat:

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: