devd in jail
Giulio Ferro
auryn at zirakzigil.org
Tue Sep 5 12:32:59 UTC 2017
Hi Alexander,
This set of patches doesn't seem to apply to 11.1 stable, am I right?
> Il giorno 10 ago 2017, alle ore 22:54, Alexander Leidinger <Alexander at leidinger.net> ha scritto:
>
>
> Quoting Alan Somers <asomers at freebsd.org> (from Wed, 9 Aug 2017 13:14:20 -0600):
>
>>> On Wed, Aug 9, 2017 at 12:47 PM, Giulio Ferro <auryn at zirakzigil.org> wrote:
>>> Hello all,
>>>
>>> Setup : 11.1-STABLE FreeBSD 11.1-STABLE #0 r321925M amd64
>>>
>>>
>>> I'm trying to create a fully virtualized desktop enviroment in a jail by
>>> means of installing there
>>> a xrdp-devel server + Xorg installation (xorg + xorgrdp).
>>>
>>> Everything seems to work until the moment when the X server actually tries
>>> to come up (after I choose session=xorg, username + password)
>>> In the X logs in the jail, in fact, I have this error:
>>>
>>> ...
>>> [ 9768.824] (EE) config/devd: fail to connect to devd
>>> [ 9768.824] [config] failed to initialise devd
>>>
>>>
>>> I've checked on the host machine, and I don't have that error as everything
>>> works fine there...
>>>
>>> In my jail, I've setup the devfs like this (/etc/jail.conf in the host):
>>>
>>> ---
>>> exec.start="/bin/sh /etc/rc";
>>> exec.stop="/bin/sh /etc/rc.shutdown";
>>> exec.clean;
>>> mount.devfs;
>>> devfs_ruleset=1;
>>>
>>> path="/usr/home/jail/$name";
>>>
>>> myjail {
>>> host.hostname="myjail.me.com";
>>> vnet;
>>> vnet.interface = epair0b, epair1b;
>>> persist;
>>> }
>>> ---
>>>
>>>
>>> and in the /etc/devfs.conf everythink is commented out.
>>>
>>> In the /dev directory in the jail, I get both the devctl and devctl2
>>> devices.
>>>
>>> As the devd demon is not running in the jail, I've tried adding
>>> devd_enable="YES"
>>>
>>> in the rc.conf (jail), but when I try to start it, I get:
>>>
>>> # /etc/rc.d/devd start
>>> Starting devd.
>>> devd: Can't open devctl device /dev/devctl: Device busy
>>> /etc/rc.d/devd: WARNING: failed to start devd
>>>
>>>
>>> Do you know if I'm doing something wrong, or there's a proper way to have
>>> devd running in the jail?
>>>
>>> I've thought that maybe I should use the devtcl2 device, as the devctl is
>>> used by the host,
>>> but I don't know how to specify that to devd...
>>>
>>> Thanks in advance for your help.
>>>
>>> Giulio
>>
>> Unfortunately, you're not going to be able to run devd(8) in the jail.
>> /dev/devctl can be opened by only one reader at a time, and that
>> reader is always devd(8). /dev/devctl2 is actually a completely
>> different device with a totally different interface. Apologies for
>> the confusing names. But you may not need to run a totally separate
>> instance of devd. The X server is probably trying to open either
>> /var/run/devd.pipe or /var/run/devd.seqpacket.pipe. ktrace would tell
>> you which. If you can bridge those sockets into the jail, then X
>> would probably run.
>
> Apart from using an explicit config of devices instead of HAL / devd, if this is a X server connecting to a graphics card (instead of just a remote accessible framebuffer), the X-in-a-jail patches are needed, as the X server needs access to /dev/(k)mem and /dev/io (and /dev/drm).
>
> ATTENTION: doing this compromises the complete security of the entire machine. The jail with the X-server can then access the entire memory of the machine, this means circumventing any kernel-level security protection / jail restrictions.
>
> Using the PR_ALLOW_* flags from current in 11.1 is ok (sys/sys/jail.h):
> ---snip---
> /* Flags for pr_allow */
> #define PR_ALLOW_SET_HOSTNAME 0x00000001
> #define PR_ALLOW_SYSVIPC 0x00000002
> #define PR_ALLOW_RAW_SOCKETS 0x00000004
> #define PR_ALLOW_CHFLAGS 0x00000008
> #define PR_ALLOW_MOUNT 0x00000010
> #define PR_ALLOW_QUOTAS 0x00000020
> #define PR_ALLOW_SOCKET_AF 0x00000040
> #define PR_ALLOW_MOUNT_DEVFS 0x00000080
> #define PR_ALLOW_MOUNT_NULLFS 0x00000100
> #define PR_ALLOW_MOUNT_ZFS 0x00000200
> #define PR_ALLOW_MOUNT_PROCFS 0x00000400
> #define PR_ALLOW_MOUNT_TMPFS 0x00000800
> #define PR_ALLOW_MOUNT_FDESCFS 0x00001000
> #define PR_ALLOW_MOUNT_LINPROCFS 0x00002000
> #define PR_ALLOW_MOUNT_LINSYSFS 0x00004000
> #define PR_ALLOW_RESERVED_PORTS 0x00008000
> #define PR_ALLOW_KMEM_ACCESS 0x00010000 /* reserved, not used yet */
> #define PR_ALLOW_ALL 0x0001ffff
> ---snip---
>
> Then kern_jail.c needs a little patch:
> ---snip---
> Index: sys/kern/kern_jail.c
> ===================================================================
> --- sys/kern/kern_jail.c (revision 321365)
> +++ sys/kern/kern_jail.c (working copy)
> @@ -200,6 +200,7 @@
> "allow.mount.linprocfs",
> "allow.mount.linsysfs",
> "allow.reserved_ports",
> + "allow.kmem_access",
> };
> const size_t pr_allow_names_size = sizeof(pr_allow_names);
>
> @@ -220,6 +221,7 @@
> "allow.mount.nolinprocfs",
> "allow.mount.nolinsysfs",
> "allow.noreserved_ports",
> + "allow.nokmem_access",
> };
> const size_t pr_allow_nonames_size = sizeof(pr_allow_nonames);
>
> @@ -3344,6 +3346,27 @@
> return (0);
>
> /*
> + * Allow access to /dev/io in a jail if the non-jailed admin
> + * requests this and if /dev/io exists in the jail. This
> + * allows Xorg to probe a card.
> + */
> + case PRIV_IO:
> + if (cred->cr_prison->pr_allow & PR_ALLOW_KMEM_ACCESS)
> + return (0);
> + else
> + return (EPERM);
> +
> + /*
> + * Allow low level access to KMEM-like devices (e.g. to
> + * allow Xorg to use DRI).
> + */
> + case PRIV_KMEM_WRITE:
> + if (cred->cr_prison->pr_allow & PR_ALLOW_KMEM_ACCESS)
> + return (0);
> + else
> + return (EPERM);
> +
> + /*
> * Allow jailed root to set loginclass.
> */
> case PRIV_PROC_SETLOGINCLASS:
> ---snip---
>
> For 11.1 one little change is needed to get DRM access... see https://svnweb.freebsd.org/changeset/base/320827
>
> The jail then needs to be started with "allow.kmem_access" and appropriate devfs rules (the jail needs rule 15 or 18, you may want to give more or less access, depending on your needs, review with care):
> ---snip---
> [devfsrules_unhide_audio=5]
> add path 'audio*' unhide
> add path 'dsp*' unhide
> add path midistat unhide
> add path 'mixer*' unhide
> add path 'music*' unhide
> add path 'sequencer*' unhide
> add path sndstat unhide
> add path speaker unhide
>
> [devfsrules_unhide_input=7]
> add path 'atkbd*' unhide
> add path 'kbd*' unhide
> add path 'joy*' unhide
> add path 'psm*' unhide
> add path sysmouse unhide
> add path 'ukbd*' unhide
> add path 'ums*' unhide
>
> [devfsrules_unhide_xorg=8]
> add path agpgart unhide
> #add path console unhide
> add path dri unhide
> add path 'dri/card*' unhide
> add path nvidiactl unhide
> add path 'nvidia*' unhide
> add path io unhide
> add path mem unhide
> add path pci unhide
> add path tty unhide
> add path ttyv0 unhide
> add path ttyv1 unhide
> add path ttyv8 unhide
>
> [devfsrules_unhide_kmem=11]
> add path kmem unhide
>
> [devfsrules_unhide_zfs=12]
> add path zfs unhide
>
> #
> # This allows to run a desktop system in a jail. Think about what you want to
> # achieve before you use this, it opens up the entire machine to access from
> # this jail to any sophisticated program.
> #
> [devfsrules_jail_desktop=15]
> add include $devfsrules_hide_all
> add include $devfsrules_unhide_basic
> add include $devfsrules_unhide_login
> add include $devfsrules_unhide_audio
> add include $devfsrules_unhide_input
> add include $devfsrules_unhide_xorg
> add include $devfsrules_unhide_kmem
>
> [devfsrules_jail_desktop_withzfs=18]
> add include $devfsrules_hide_all
> add include $devfsrules_unhide_basic
> add include $devfsrules_unhide_login
> add include $devfsrules_unhide_audio
> add include $devfsrules_unhide_input
> add include $devfsrules_unhide_xorg
> add include $devfsrules_unhide_kmem
> add include $devfsrules_unhide_zfs
> ---snip---
>
> Bye,
> Alexander.
>
> --
> http://www.Leidinger.net Alexander at Leidinger.net: PGP 0x8F31830F9F2772BF
> http://www.FreeBSD.org netchild at FreeBSD.org : PGP 0x8F31830F9F2772BF
More information about the freebsd-hackers
mailing list