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Date:      Wed, 16 Sep 2015 11:30:33 -0500
From:      Kevin Day <toasty@dragondata.com>
To:        freebsd-fs@freebsd.org
Subject:   Neutered devices in jails (per FS flag?)
Message-ID:  <E0C9157B-0FB7-4B2B-9BA2-5779DA7877FF@dragondata.com>

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We=E2=80=99re currently using jails to allow servers to copy backups of =
themselves to a central backup server. The problem we=E2=80=99re having =
is with mknod/devices. Currently jails don=E2=80=99t allow device files =
to be created, which makes sense - you don=E2=80=99t want them to be =
able to bypass the jail by opening /dev/kmem or something. We want jails =
to be able to create device files, just not be able to open/use them.

Has anyone given any thought to changing this behavior? Allowing jails =
to create/manipulate device files, but not actually opening them? I.e. =
instead of returning EPERM on creating the device, instead return EPERM =
on opening it? This would likely need to be a filesystem flag, because =
jails still require some devices to work (a separate devfs mount or =
something). We could make the jail=E2=80=99s /dev read only or use devfs =
so those devices still work, but have the parent jail directory with a =
=E2=80=9Cnoopendev=E2=80=9D flag or something similar.

Has anyone gone down this path before?

=E2=80=94 Kevin





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