netdev - Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

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Message-ID: <m1lje2qzf4.fsf@fess.ebiederm.org>
Date:	Mon, 08 Mar 2010 13:25:03 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Daniel Lezcano <daniel.lezcano@...e.fr>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Serge Hallyn <serue@...ibm.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Ben Greear <greearb@...delatech.com>
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

Daniel Lezcano <daniel.lezcano@...e.fr> writes:

> Eric W. Biederman wrote:
>> Daniel Lezcano <daniel.lezcano@...e.fr> writes:
>>
>>   
>>> Eric W. Biederman wrote:
>>>     
>>>> Daniel Lezcano <daniel.lezcano@...e.fr> writes:
>>>>
>>>>         
>>>>> Eric W. Biederman wrote:
>>>>>             
>>>>>> Daniel Lezcano <daniel.lezcano@...e.fr> writes:
>>>>>>
>>>>>>                   
>>>>>>> Eric W. Biederman wrote:
>>>>>>>                         
>>>>>>>> I have take an snapshot of my development tree and placed it at.
>>>>>>>>
>>>>>>>>
>>>>>>>> git://git.kernel.org/pub/scm/linux/people/ebiederm/linux-2.6.33-nsfd-v5.git
>>>>>>>>                                 
>>>>>>> Hi Eric,
>>>>>>>
>>>>>>> thanks for the pointer.
>>>>>>>
>>>>>>> I tried to boot the kernel under qemu and I got this oops:
>>>>>>>                         
>>>>>> I am clearly running an old userspace on my test machine.  No udev.
>>>>>> It looks like udev has a long standing netlink misfeature, where
>>>>>> it does not initializing NETLINK_CB....
>>>>>>
>>>>>>
>>>>>> >From 8d85e3ab88718eda3d94cf8e1be14b69dae2b8f1 Mon Sep 17 00:00:00 2001
>>>>>> From: Eric W. Biederman <ebiederm@...ssion.com>
>>>>>> Date: Mon, 8 Mar 2010 09:25:20 -0800
>>>>>> Subject: [PATCH] kobject_uevent:  Use the netlink allocator helper...
>>>>>>
>>>>>> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
>>>>>>                   
>>>>> Thanks.
>>>>>
>>>>> I was able to boot but I have the following warning:
>>>>>             
>>>> Thanks for the bug report.
>>>>         
>>> Thanks to you for the patchset :)
>>>
>>>     
>>>> For the moment you might want to drop:
>>>> af_netlink:  Allow credentials to work across namespaces.
>>>> af_netlink: Debugging in case I have missed something.
>>>>
>>>> Although I am curious if you hit my debugging messages in
>>>> netlink recv.
>>>>         
>>> No, it does not appear (looked for "missing NETLINK_CB proto").
>>>
>>>     
>>>> I guess if the goal is to test my nsfd bits you can drop everything
>>>> starting with my 'scm: Reorder scm_cookie.' commit.  The rest is what
>>>> it takes to get get uids, gid and pids translated when the cross
>>>> namespaces on an af_unix of an af_netlink socket.
>>>>
>>>> At least in the af_netlink case it appears clear I am have missed
>>>> something.
>>>>
>>>> This is a warning that netlink throws when the packet accounting messed
>>>> up.  So it sounds like you are exercising another path that I failed
>>>> to exercise and fix.
>>>>         
>>> I will look forward if I find more clues for this warning.
>>>
>>> In the meantime  was able to enter the container with the ugly following
>>> program:
>>>
>>> #include <unistd.h>
>>> #include <stdlib.h>
>>> #include <stdio.h>
>>> #include <syscall.h>
>>> #include <sys/types.h>
>>> #include <sys/stat.h>
>>> #include <fcntl.h>
>>> #include <sys/param.h>
>>>
>>> #define __NR_setns 300
>>>
>>> int setns(int nstype, int fd)
>>> {
>>>    return syscall (__NR_setns, nstype, fd);
>>> }
>>>
>>> int main(int argc, char *argv[])
>>> {
>>>    char path[MAXPATHLEN];
>>>    char *ns[] = { "pid", "mnt", "net", "pid", "uts" };
>>>    const int size = sizeof(ns) / sizeof(char *);
>>>    int fd[size];
>>>    int i;
>>>
>>>    if (argc != 3) {
>>>        fprintf(stderr, "mynsenter <pid> <command>\n");
>>>        exit(1);
>>>    }
>>>
>>>    for (i = 0; i < size; i++) {
>>>            sprintf(path, "/proc/%s/ns/%s", argv[1], ns[i]);
>>>
>>>        fd[i] = open(path, O_RDONLY);
>>>        if (fd[i] < 0) {
>>>            perror("open");
>>>            return -1;
>>>        }
>>>
>>>    }
>>>
>>>    for (i = 0; i < size; i++) {
>>>
>>>        if (setns(0, fd[i])) {
>>>            perror("setns");
>>>            return -1;
>>>        }
>>>    }
>>>
>>>    execve(argv[2], &argv[2], NULL);
>>>    perror("execve");
>>>
>>>    return 0;
>>> }
>>>
>>> At the fist glance, no problem :)
>>>     
>>
>> No fork() so your processes is completely in the pid namespace?
>>   
> What I do is to attach "/bin/sh" to the container with this program.
> The container is a VPS running busybox with the full isolation.
>
> echo $$ gives the real pid.
> All the forked processes appears in the pid namespace, they are visible through
> /proc with the virtual pid.
> I am not able to change to the /proc/self directory (I assume this is normal).

I guess my meaning is I was expecting.
child = fork();
if (child == 0) {
	execve(...);
}
waitpid(child);

This puts /bin/sh in the container as well.

I'm not certain about the /proc/self thing I have never encountered that.
But I guess if your pid is outside of the pid namespace of that instance
of proc /proc/self will be a broken symlink.

Eric

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