Date: Tue, 3 Jan 2006 09:57:28 +0200 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Tzachi Tager <tzachi_tager@yahoo.com> Cc: freebsd-bugs@freebsd.org Subject: Re: using /dev/null in chrooted enviroment Message-ID: <20060103075728.GA81689@flame.pc> In-Reply-To: <20051228091604.48873.qmail@web30805.mail.mud.yahoo.com> References: <20051228032332.GA30303@flame.pc> <20051228091604.48873.qmail@web30805.mail.mud.yahoo.com>
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On 2005-12-28 01:16, Tzachi Tager <tzachi_tager@yahoo.com> wrote:
> Hi,
>
> Giorgos Keramidas <keramida@freebsd.org> wrote: On 2005-12-27 06:49, Tzachi Tager wrote:
> > Hi,
> > I'm trying to create chrooted enviroment, i did the folllowing
> > in the chrooted enviroment:
> >
> > mknode c null 0 24
> > mknode c zero 0 25
> >
> > And then i did chroot and those files are under /dev, but when
> > i wrote a short program in C that tries to open /dev/null
> > (within the chrooted env.) i got:
> >
> > "/dev/null-operation is not supported"
>
> > You forgot to mention what version of FreeBSD you are using. It
> > may also help to see the contents of the chrooted /dev directory.
>
> We are using:
>
> FreeBSD freebsd6.0 6.0-RELEASE FreeBSD 6.0-RELEASE #0:
> Thu Nov 3 09:36:13 UTC 2005
> root@x64.samsco.home:/usr/obj/usr/src/sys/GENERIC i386
>
> We tried:
>
> 1) To create only /dev/null and /dev/zero (that configuration worked in FreeBSD 5.4)
> 2) To create the same /dev contents via: tar -cf - /dev | tar -xf -
>
> The original system has /dev mounted as: devfs on /dev (devfs, local)
That's not the correct way to populate a /dev directory in a chroot
anymore. None of the above will work as expected, AFAIK. The best way
to create a second devfs mount-point that only contains /dev/zero and
/dev/null is to remount devfs and 'hide' all teh rest of the device
nodes:
> PS: It seems like if we mount devfs to the chrooted env - everything
> works. The problem is that chroot directory can be placed everywhere,
> but mount doesn't accept very long path:
>
> # mount -t devfs none dev
> mount_devfs: File name too long
>
> # pwd
> /tmp/build.debugger-php-4.0.6.5269/debugger-php-4.0.6-DEBUG_SERVER_5_1_0_RC3_20051215
This is where you hit an internal limit of the kernel. The limit is
defined as 88 bytes at /usr/src/sys/sys/mount.h:
# root@flame:/usr/src/sys/sys# grep MNAMELEN mount*
# #define MNAMELEN 88 /* size of on/from name bufs */
# char f_mntfromname[MNAMELEN]; /* mounted filesystem */
# char f_mntonname[MNAMELEN]; /* directory on which mounted */
I'm not sure if this is easy to bump. The best person to answer is
someone with more experience with the kernel internals.
A workaround that you can use in the mean time is to use shorter names
for the chroot directories, i.e.:
# mkdir -p /tmp/chroot/100/dev
# mount -t devfs devfs /tmp/chroot/100/dev
Regards,
Giorgos
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