Re: when is VFCF_JAIL allowed?

On Mon, Feb 12, 2024, at 10:16 AM, Brooks Davis wrote:
> On Mon, Feb 12, 2024 at 10:02:01AM -0800, Chuck Tuffli wrote:
> > I was experimenting with a workflow and needed to allow a jail to mount an ISO image. This fails because the cd9660 file system does not set VFCF_JAIL:
> >                       can be mounted from within a jail if allow.mount and
> >                       allow.mount.<vfc_name> jail parameters are set
> > Is there a reason jails should not be allowed to mount an ISO or is it because no one has added the support?
> 
> File systems where the kernel parses a binary disk image aren't generally
> safe because a bad image can corrupt kernel state.  It should be safe
> and allowed to mount an ISO via fusefs (not sure if we have a module
> available in ports, but I'd guess so.)
Thanks for the feedback, Brooks. This makes sense, but I must be missing the safety difference between host and the jail. On the host, I can do:

# mdconfig -a -t vnode -f ./seed.iso -u 1
# mount_cd9660 /dev/iso9660/cidata /media/

Does this not run the same risk of corrupting kernel state, or maybe this is a bug?

I'm also noticing the msdosfs cannot be mounted in a jail either:

$ lsvfs cd9660 msdosfs
Filesystem                              Num  Refs  Flags
-------------------------------- ---------- -----  ---------------
cd9660                           0x000000bd     0  read-only
msdosfs                          0x00000032     1

Is there a similar issue with this file system as well?

--chuck