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From: "Leibowitz, Michael" <michael.leibowitz@intel.com>
To: <serge@hallyn.com>
Cc: <linux-kernel@vger.kernel.org>
Subject: RE: CLONE_NEWNS and bind mounts to make "chroot" jail
Date: Sun, 2 Mar 2008 22:56:40 -0800	[thread overview]
Message-ID: <645B0EE4078B7C49A6C12F5E7B3B6C2603D3D7BF@orsmsx418.amr.corp.intel.com> (raw)
In-Reply-To: <20080302022655.GA28450@vino.hallyn.com>

If I understand correctly, the following should accomplish what I'm
looking for.  However, pivot_root gives me EBUSY.  I played around with
moving the mount --bind /jail /jail to before the unshared, as well as
making old_root a bind mount to itself.  However, pivot_root always
seems to fail.  Is there something obvious that I'm doing wrong?  The
following is my test code (error checking has been removed for clarity,
except for pivot_root).  

  char *newargv[]= { "sh", NULL };

  chdir("/jail");
  unshare(CLONE_NEWNS));
  mount("/jail", "/jail", NULL, MS_BIND, NULL));
  mount("/bin", "bin", NULL, MS_BIND, NULL));
  mount("/usr", "usr", NULL, MS_BIND, NULL));
  mount("/lib", "lib", NULL, MS_BIND, NULL));
  if (pivot_root(".", "old_root")) perror("pivot_root . old_root");
  exec("./bash-static"); /* copied to /jail prior to running */

Thanks. 

>Serge replies:
 [snip...snip]
>Try a few more things.  Since you had entered /jail, you can view '/'
by
>looking at .. .  But if you look at /, you dereference your
>task->fsroot.  You never changed that, so it points to the original
>mount.  If however you 'ls ..', you should see your 'jail' directory.
>However it won't have the /bin and /lib mounted because you didn't
>	mount --rbind /jail /
>What you really want to do is
>	mount --bind /jail /jail
>to make sure it's a mountpoint, then set up the new /jail using bind
>mounts like you're doing (and likely some rbinds in some places), then
>use pivot_root() to change your root.  Then umount2("/old_root",
>MNT_DETACH).
>
>-serge

--
Michael Leibowitz
Software Engineer, UMG
Intel Corporation
michael.leibowitz at intel.com



  reply	other threads:[~2008-03-03  6:58 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-01 17:05 Leibowitz, Michael
2008-03-02  2:26 ` serge
2008-03-03  6:56   ` Leibowitz, Michael [this message]
2008-03-04 21:45     ` serge
2008-03-05  6:23       ` Leibowitz, Michael
     [not found] <a2DnP-4KR-9@gated-at.bofh.it>
     [not found] ` <a2M7M-1rM-5@gated-at.bofh.it>
     [not found]   ` <a3cOQ-1eQ-3@gated-at.bofh.it>
2008-03-03 15:54     ` Bodo Eggert

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