Re: [vserver] /proc/mounts

[Paul Sladen]

On Thu, 14 Aug 2003, Herbert P�tzl wrote:
> On Thu, Aug 14, 2003 at 01:38:36AM +0200, Bodo Eggert wrote:
> > Maybe you could change /proc/mounts into a symlink to /etc/mtab.
> would also be an option ... other suggestions?

`/proc/mounts' is actually already a symlink to `/proc/self/mounts' which is
the individual calling processes' namespace;  this could probably be
hard-coded to `../etc/mtab' [BUT, see below]:

  $ grep 'self/mounts' fs/proc/*.c
  fs/proc/proc_misc.c:    proc_symlink("mounts", NULL, "self/mounts");

The problem is that that would do it globally (it is done on bootup when
procfs is first mounted), whereas leaving `/proc/mounts' pointing at the
task's namespace will make it easier to do it per-task (really per-context).

I think the fiddling needs doing in `fs/name{space,i}.c', although I haven't
found where...  There various things along the line of:

          while (mnt->mnt_parent != mnt)
                mnt = mnt->mnt_parent;

So if it is within the current chroot, it stops iterating upwards, otherwise
if it is outside.  --We need to remove it if it is outside.

Also, have a quick skim (read) over:

  
http://www.paul.sladen.org/vserver/aspcomplete/2000-08-25/ve-0.4.2-for-2.4.0-test6.diff.gz

I just looked at it recently and noticed there are a couple of things in
there. -It seems that virtuozzo sys_reboot() is causing all the processes in
that context to be killed (something we could do with a function to cause).

Secondly, grepping the virtuozzo diff, there's some patching to:

  follow_dotdot(),  in  fs/namei.c

+#ifdef CONFIG_VE
+               if (nd->dentry == current->envid->fs_root &&
+                   nd->mnt == current->envid->fs_rootmnt)  {
+                       read_unlock(&current->fs->lock);
+                       break;
+               }
+#endif

  [envid is equivalent to vserver's ctx]

which maybe related...?  (Or that could be chroot() protection).

Happy investigating!

        -Paul
-- 
War is inconsistent with Truth.  Nottingham, GB