misc/121385: unionfs cross mount -> kernel panic

[Rick van der Zwet]

>Number:         121385
>Category:       misc
>Synopsis:       unionfs cross mount -> kernel panic
>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:   Wed Mar 05 11:20:03 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Rick van der Zwet
>Release:        FreeBSD-7-STABLE
>Organization:
Stichting Wireless Leiden
>Environment:
FreeBSD  7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sun Feb 24 19:59:52 UTC 2008     root at logan.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386

>Description:
Able to crash/freeze kernel when accidentally mounting to directories on top of each-other using unionfs 
>How-To-Repeat:
# mkdir -p /unionfs/disk1
# mkdir -p /unionfs/disk2
# mount -t unionfs /unionfs/disk1 /unionfs/disk2
# mount -t unionfs /unionfs/disk2 /unionfs/disk1
# touch /unionfs/disk1/foo
<freeze or crash>
>Fix:
Workaround: carefully check your syntax when mounting

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