[CRIU] [PATCH v3 06/26] files: Allow to receive further fds

[Pavel Emelyanov]

On 12/06/2016 09:11 PM, Kirill Tkhai wrote:
> On 06.12.2016 21:13, Pavel Emelyanov wrote:
>> On 12/06/2016 08:19 PM, Kirill Tkhai wrote:
>>>
>>>
>>> On 06.12.2016 20:16, Pavel Emelyanov wrote:
>>>>
>>>>>  int recv_fd_from_peer(struct fdinfo_list_entry *fle)
>>>>>  {
>>>>>  	struct fdinfo_list_entry *tmp;
>>>>>  	int fd, ret;
>>>>>  
>>>>> +	if (fle->received)
>>>>> +		return fle->fe->fd;
>>>>> +again:
>>>>>  	ret = recv_fds(fle->fe->fd, &fd, 1, (void *)&tmp, sizeof(struct fdinfo_list_entry *));
>>>>>  	if (ret)
>>>>>  		return -1;
>>>>>  
>>>>>  	if (tmp != fle) {
>>>>> -		pr_err("Received wrong fle\n");
>>>>> -		return -1;
>>>>> +		pr_info("Further fle=%p, pid=%d\n", tmp, fle->pid);
>>>>> +		if (!task_fle(current, fle)) {
>>>>
>>>> OK, so this routine makes sure the fle received sits in current's list.
>>>> Two questions: 1. should we consider receiving of non-current fle as BUG()?
>>>
>>> Yes, it's a BUG. We fail restore if so.
>>
>> OK, so I'll change this return -1 to BUG() instead.
>>
>>>> and 2. can we make the same check by comparing fle->pid with current? All
>>>> fle's are in shmem, so contents is accessible by everyone.
>>>
>>> It seems to be worse, because if there is a problem with fle, it may point
>>> to a random memory. So fle->pid dereference will finish with SIGSEGV.
>>
>> But it can point to a random memory only if someone sends in this descriptor
>> anything, but fle, right? All fle-s are accessible by anyone.
> 
> If we do not consider the case with malefactor, then it's only fle, yes.

I will change this check for pid mismatch then, OK?

-- Pavel