linux-kernel - Re: [PATCH] Convert BUG_ON to WARN_ON in bond

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Date:   Thu, 22 Jun 2017 00:04:54 +0100
From:   Michael J Dilmore <michael.j.dilmore@...il.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     David Miller <davem@...emloft.net>, vfalico@...il.com,
        andy@...yhouse.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, joe@...ches.com
Subject: Re: [PATCH] Convert BUG_ON to WARN_ON in bond_options.c

On 21/06/17 23:39, Jay Vosburgh wrote:
> Michael J Dilmore <michael.j.dilmore@...il.com> wrote:
>
>> On 21/06/17 22:56, David Miller wrote:
>>
>>> From: Michael D <michael.j.dilmore@...il.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
>> }
> 	In general, yes, but in this case, the condition should be
> impossible to hit, so BUG_ON seems appropriate.
>
> 	If bond_slave_get_rtnl/rcu() returns NULL for an actual bonding
> slave, other code paths (bond_fill_slave_info, bond_handle_frame) will
> likely crash before getting to this one.
>
> 	-J
>
> ---
> 	-Jay Vosburgh, jay.vosburgh@...onical.com
That did cross my mind but I read that Linus that was quite averse to 
BUG_ON anywhere in the kernel so thought it might be have been worth doing.

Is it worth at least wrapping BUG_ON in an unlikely macro then?