netdev - Re: [PATCH 1/3] dev: Prevent creating network devices with negative ifindex

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Date:   Fri, 16 Jun 2017 19:44:45 +0300
From:   Serhey Popovych <serhe.popovych@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH 1/3] dev: Prevent creating network devices with negative
 ifindex


> On Fri, 16 Jun 2017 17:23:51 +0300
> Serhey Popovych <serhe.popovych@...il.com> wrote:
> 
>> Interface index is signed integer, we can pass ifm->ifi_index
>> from userspace via netlink and create network device with
>> negative ifindex value.
>>
>> Fixes: 9c7dafbfab15 ("net: Allow to create links with given ifindex")
>> Signed-off-by: Serhey Popovych <serhe.popovych@...il.com>
>> ---
>>  net/core/dev.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 8658074..dae8010 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -7491,7 +7491,7 @@ int register_netdevice(struct net_device *dev)
>>  	}
>>  
>>  	ret = -EBUSY;
>> -	if (!dev->ifindex)
>> +	if (dev->ifindex <= 0)
>>  		dev->ifindex = dev_new_index(net);
>>  	else if (__dev_get_by_index(net, dev->ifindex))
>>  		goto err_uninit;
> 
> You should fix this by adding error check in the netlink portion
> that allows creating devices with given ifindex. Passing < 0
> should be an error.But should this break some setups if I add such check to netlink
portion? In my opinion it is better to choose silently different
ifindex rather than reporting failure. That's why I prefer doing
this in register_netdevice().

Also there is similar problem for drivers/net/veth.c, it might
happen that other places will be added later that setup
dev->ifindex and then call register_netdevice().

What do you think?

Thanks for quick review!

> 

-- 
Thanks, Serhey