[CRIU] RPC support for --shell-job missing on restore

[Ruslan Kuprieiev]

On 16.05.2014 17:20, Andrew Vagin wrote:
> On Fri, May 16, 2014 at 05:16:02PM +0300, Ruslan Kuprieiev wrote:
>> On 16.05.2014 17:08, Andrew Vagin wrote:
>>> On Fri, May 16, 2014 at 04:49:16PM +0300, Ruslan Kuprieiev wrote:
>>>> On 16.05.2014 16:28, Andrew Vagin wrote:
>>>>> On Fri, May 16, 2014 at 08:33:41AM -0400, Christopher Covington wrote:
>>>>>> Hi Allan,
>>>>>>
>>>>>> On 05/16/2014 03:44 AM, Allan Cecil wrote:
>>>>>>> On 2014-05-15 06:59, Pavel Emelyanov wrote:
>>>>>>>> I'd like to notice here, that right now this is only possible if you
>>>>>>>> terminate the whole existing process and
>>>>>>>> restore one back from scratch using criu. However, we have a feature
>>>>>>>> called "applying images" (http://criu.org/Applying_images)
>>>>>>>> With it you will not have to kill the original process and the
>>>>>>>> revert-back should become MUCH faster.
>>>>>>> Applying images sounds very interesting - how do I do that?  I don't see it in
>>>>>>> the man page.  I've built from source so I can update or switch branches as
>>>>>>> needed.
>>>>>>>
>>>>>>>> You might b einterested in the --exec-cmd option for criu. It causes
>>>>>>>> criu to call execv() on whatever you want after
>>>>>>>> restore thus making _your_ code control the restored processes.
>>>>>>> I haven't figured out how to make this work, yet.  I'll keep experimenting.  I
>>>>>>> thought it was for saying "restore this into this screen session" but that did
>>>>>>> not work.
>>>>>>>
>>>>>>>>> that would still work.  Unfortunately, even if I set the suid bit and
>>>>>>>>> attempt to restore from the command line I still get denied
>>>>>>>>> bgecause the UID / GID doesn't match.
>>>>>>>> Can you shed more light on this? We tried to make it work like -- if
>>>>>>>> we have images for user X, then if we restore from
>>>>>>>> them from suid-ed criu and the user that does so is X as well, then we
>>>>>>>> allow for that. Has that get broken?
>>>>>>>>
>>>>>>> Here are the exact steps I'm taking.  First, I'm running as the unprivileged
>>>>>>> user named tas:
>>>>>>> $ id
>>>>>>> uid=1001(tas) gid=1001(tas) groups=1001(tas),110(kvm),119(nopasswdlogin)
>>>>>>>
>>>>>>> I start screen and inside of screen I start nethack.  This produces the
>>>>>>> following ps axf -o pid,sid,pgid,uid,gid,comm output:
>>>>>>>
>>>>>>>   9002  9002  9002  1001    43 screen
>>>>>>>   9003  9003  9003  1001  1001  \_ bash
>>>>>>>   9165  9003  9165  1001  1001      \_ nethack
>>>>>>>
>>>>>>> If outside of screen I attempt to issue the command criu dump -v4 -t 9002 as
>>>>>>> the same tas user I get this:
>>>>>>>
>>>>>>> (00.014062) Obtaining task stat ... (00.014126) Error (security.c:34): UID/GID
>>>>>>> mismatch 1001 != (1001,43,43)
>>>>>> It looks like the session ID isn't matching.
>>>>> I have reproduce this bug on my host.
>>>>>
>>>>> (00.012437) Obtaining task stat ... (00.012592) Error (security.c:34): UID/GID mismatch 1000 != (1000,20,20)
>>>>>
>>>>> [avagin at localhost criu]$ ps -C nethack
>>>>>    PID TTY          TIME CMD
>>>>> 10962 pts/2    00:00:00 nethack
>>>>> [avagin at localhost criu]$ cat /proc/10962/status | grep Gid
>>>>> Gid:	1000	20	20	20
>>>>>
>>>>> [avagin at localhost zzz]$ cat /etc/group | grep 20
>>>>> games:x:20:
>>>>>
>>>>> Add Ruslan Kuprieiev in CC. He is the main security specialist in CRIU;)
>>>> Thanks Andrew. =)
>>>>
>>>> If i get it right, there are some typos in check_ids() from security.c:
>>>> static bool check_ids(unsigned int crid, unsigned int rid, unsigned int eid,
>>>> unsigned int sid)
>>>> {
>>>>      if (crid == 0)
>>>>          return true;
>>>>      if (crid == rid && crid == eid && crid == sid) // Here probably should
>>>> be "||"s instead of "&&"s
>>>>          return true;
>>>>
>>>>      pr_err("UID/GID mismatch %u != (%u,%u,%u)\n", crid, rid, eid, sid);
>>>>      return false;
>>>> }
>>>>
>>>> Does it look right to you? If so, will send patch.
>>> Yes, it does. Is it correct that if we can kill a task, we should be
>>> able to dump it?
>> Looks correct to me.
>>
>>> static int kill_ok_by_cred(struct task_struct *t)
>>> {
>>>          const struct cred *cred = current_cred();
>>>          const struct cred *tcred = __task_cred(t);
>>>
>>>          if (uid_eq(cred->euid, tcred->suid) ||
>>>              uid_eq(cred->euid, tcred->uid)  ||
>>>              uid_eq(cred->uid,  tcred->suid) ||
>>>              uid_eq(cred->uid,  tcred->uid))
>>>                  return 1;
>>>
>>>          if (ns_capable(tcred->user_ns, CAP_KILL))
>>>                  return 1;
>>>
>>>          return 0;
>>> }
>>>
>> Sorry if I didn't get smth right, but where and why do you want to put this
>> function(kill_ok_by_cred)?
> This function from the linux kernel is used to check permission to kill
> a "t" task

Oh, I see.=) Thanks.
Will send patch ASAP.

>>>>>>> (00.014137) Error (cr-dump.c:1438): Check uid (pid: 9002) failed
>>>>>>>
>>>>>>> For the record, the criu process has the stuid bit set:
>>>>>>>
>>>>>>> -rwsr-xr-x 1 root root 779899 Apr 25 14:39 /usr/local/sbin/criu
>>>>>>>
>>>>>>> I'm not sure what to make of this.  Thanks for your thoughts,
>>>>>> Can you try `criu dump` of `setsid nethack` instead of `criu dump -j` of
>>>>>> `nethack`.
>>>>>>
>>>>>> Regards,
>>>>>> Christopher
>>>>>>
>>>>>> -- 
>>>>>> Employee of Qualcomm Innovation Center, Inc.
>>>>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>>>>> hosted by the Linux Foundation.
>>>> -- 
>>>> Signed-off-by: Ruslan Kuprieiev kupruser at gmail.com
>>>>
>>
>> -- 
>> Signed-off-by: Ruslan Kuprieiev kupruser at gmail.com
>>


-- 
Signed-off-by: Ruslan Kuprieiev kupruser at gmail.com