[Devel] Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

[Miklos Szeredi]

> As I said earlier, I see a case where two mounts that are peers of each
> other can become un-identical if we dont propagate the "allowusermnt".
> 
> As a practical example.
> 
> /tmp and /mnt are peers of each other.
> /tmp has its "allowusermnt" flag set, which has not been propagated
> to /mnt.
> 
> now a normal-user mounts an ext2 file system under /tmp at /tmp/1
> 
> unfortunately the mount wont appear under /mnt/1 

Argh, that is not true.  That's what I've been trying to explain to
you all along.

The propagation will be done _regardless_ of the flag.  The flag is
only checked for the parent of the _requested_ mount.  If it is
allowed there, the mount, including any propagations are allowed.  If
it's denied, then obviously it's denied everywhere.

> and in case if you allow the mount to appear under /mnt/1, you will
> break unpriviledge mounts semantics which promises: a normal user will
> not be able to mount at a location that does not allow user-mounts.

No, it does not promise that.  The flag just promises, that the user
cannot _request_ a mount on the parent mount.

Miklos