Subject: Re: [ABI REVIEW][PATCH 0/8] Namespace file descriptors

From: Daniel Lezcano <[email-masked]>
Date: Fri, 24 Sep 2010 15:49:48 +0200

On 09/24/2010 03:02 PM, Andrew Lutomirski wrote:
> Eric W. Biederman wrote:
>> Introduce file for manipulating namespaces and related syscalls.
>> files:
>> /proc/self/ns/<nstype>
>>
>> syscalls:
>> int setns(unsigned long nstype, int fd);
>> socketat(int nsfd, int family, int type, int protocol);
>>
>
> How does security work?  Are there different kinds of fd that give (say) pin-the-namespace permission, socketat permission, and setns permission?

AFAICS, socketat, setns and "set netns by fd" only accept fd from 
/proc/<pid>/ns/<ns>.

setns does :

	file = proc_ns_fget(fd);
	if (IS_ERR(file))
		return PTR_ERR(file);

proc_ns_fget checks if (file->f_op != &ns_file_operations)

socketat and get_net_ns_by_fd:

	net = get_net_ns_by_fd(fd);

this one calls proc_ns_fget.

We have the guarantee here, the fd is resulting from an open of the file 
with the right permissions.

Another way to pin the namespace, would be to mount --bind 
/proc/<pid>/ns/<ns> but we have to be root to do that ...