From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael J Dilmore <michael.j.dilmore@gmail.com>
Subject: Re: [PATCH] Convert BUG_ON to WARN_ON in bond_options.c
Date: Wed, 21 Jun 2017 23:27:41 +0100
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To: David Miller <davem@davemloft.net>
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On 21/06/17 22:56, David Miller wrote:

> From: Michael D <michael.j.dilmore@gmail.com>
> Date: Wed, 21 Jun 2017 22:41:07 +0100
>
>> I don't think you can stop it being dereferenced... you just need to
>> prevent an attacker from exploiting the null pointer dereference
>> vulnerability right? And this is done by returning the function right
>> away?
> What's all of this about an "attacker"?
>
> If there is a bug, we dererence a NULL pointer, and we should
> fix that bug.
>
> The BUG_ON() helps us see where the problem is while at the
> same time stopping the kernel before the NULL deref happens.
Ok this is starting to make sense now - went a bit off track but think 
my general thinking is ok - i.e. if we return the function with an error 
code before the dereference then this basically does the same thing as 
BUG_ON but without crashing the kernel.

Something like:

if (WARN_ON(!new_active_slave) {
     netdev_dbg("Can't add new active slave - pointer null");
     return ERROR_CODE
}