kern/81161: Images mounted through mdconfig on a read-only fs can be modified

[Ronny lam]

>Number:         81161
>Category:       kern
>Synopsis:       Images mounted through mdconfig on a read-only fs can be modified
>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:   Tue May 17 14:10:02 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Ronny lam
>Release:        5.4
>Organization:
Snow B.V.
>Environment:
FreeBSD helix.kateri.demon.nl 5.4-RELEASE-p1 FreeBSD 5.4-RELEASE-p1 #2: Tue May 17 14:26:04 CEST 2005     root at helix.kateri.demon.nl:/usr/local/obj/usr/local/src/sys/HELIX  i386
>Description:
When mounting an image through mdconfig which resides on a read-only filesystem, it is possible to changes the md-filesystem and thus change the read-only underlying filesystem. This could be by design but looks like a problem to me.
>How-To-Repeat:
boot single-user, the root filesystem is readonly
mdconfig -a -t vnode -f boot.flp 
mount /dev/md0 /mnt
touch /mnt/hello
ls /mnt
mount, root filesystem is still read-only, /mnt is read-write
umount /mnt
mdconfig -d -u 0
mdconfig -a -t vnode -f boot.flp 
mount /dev/md0 /mnt
ls /mnt


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