Re: sys_chroot+sys_fchdir Fix

["Serge E. Hallyn" <serge@hallyn.com>]

Quoting David Newall (david@davidnewall.com):
> Bill Davidsen wrote:
>> there is no question that pivot_root is intended to have breadth for more 
>> than one process. 
>
> I think it's clear from the man page that the original idea was to be able 
> to pivot_root for individual processes.  The reason it doesn't do that, the 
> reason it affects all processes, is to work around the bootstrap problem, 
> where processes that don't care what their root (or current) directory is 
> are still using the original root.
>
> An extra parameter could be added to specify which behavior is desired, 
> probably defaulting to the current behavior. That would remove the need to 
> use a chroot bug.

No reason for any new parameters to pivot_root.  Just clone your mounts
namespace first.

	unshare(CLONE_NEWNS);
	chdir(new_dir);
	pivot_root(new_dir, oldroot);

Since pivot_root actually fiddles with the vfsmnts, this is really the
only way to go about having it "work with just one process".

-serge

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