Re: [RFC][PATCH 0/8][v2]: Enable multiple mounts of devpts

[Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>]

>>> When a task does mq_open(name, flag), then name is in the mqueuefs
>>> found in current->nsproxy->mnt_namespace->mqns.
>>>
>>> But if a task does
>>>
>>> 	clone(CLONE_NEWMNT);
>>> 	mount --move /dev/mqueue /oldmqueue
>>> 	mount -o newinstance -t mqueue none /dev/mqueue
>>>
>>> then that task can find files for the old mqueuefs under
>>> /oldmqueue, while mq_open() uses /dev/mqueue since that's
>>> what it finds through its mnt_namespace.
>> That I don't like. 
>>
>> Even though posix mqueue objects can outlive a process, I don't think 
>> a process should be able to peek and poke in a message queue namespace 
>> other than his. this is the basic principle of the namespaces : 
>> isolation. Am I wrong ?
> 
> Yes you are wrong in this case.  In particular consider mounts
> propagation, which allows you to to examine both a child namespace's
> mounts namespace, and, through the child's /sys (presumably
> mounted under /vs1/sys), his network namespace and eventually
> device namespace.

but there are some accounting done which could be fooled, like the 
max number of mqueues or the number of bytes used by the mqueues which 
is on a user_struct basis. 

>> couldn't we just return EACCES ? (not posix) 
> 
> We could.  And if we think there is really no value in viewing
> a child namespace's mqueuefs then we may as well.  I just want
> to make it clear that the proposed semantics support it as an
> option.

This make sense

C.