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

[Pavel Emelyanov]

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.

-- Pavel