netns : close all sockets at unshare ?

[Daniel Lezcano]

Eric W. Biederman wrote:
> Daniel Lezcano <dlezcano at fr.ibm.com> writes:
> 
>> Hi,
>>
>> I was looking at some cornercases and trying to figure out what happens if
>> someone does:
>>
>> 1 - fd = socket(...)
>> 2 - unshare(CLONE_NEWNET)
>> 3 - bind(fd, ...) / listen(fd, ...)
>>
>> There is here an interaction between two namespaces.
>> Trying to catch all these little tricky paths everywhere with the network
>> namespace is painful, perhaps we should consider a more radical solution.
> 
> Huh?
> 
> socket() puts the namespace on struct sock.
> bind/listen etc just look at that namespace. 
> 
> Unless I'm blind it is simple and it works now.

Yes, it will work.

Do we want to be inside a network namespace and to use a socket 
belonging to another network namespace ? If yes, then my remark is 
irrelevant.

>> Shall we close all fd sockets when doing an unshare ? like a close-on-exec
>> behavior ?
> 
> I think adopting that policy would dramatically reduce the usefulness
> of network namespaces.
> 
> Making the mix and match cases gives the implementation much more flexibility
> and it doesn't appear that hard right now.

I am curious, why such functionality is useful ?