Re: [PATCH] Convert BUG_ON to WARN_ON in bond_options.c

From: Jay Vosburgh
Date: Wed Jun 21 2017 - 18:39:42 EST

Michael J Dilmore <michael.j.dilmore@xxxxxxxxx> wrote:

>On 21/06/17 22:56, David Miller wrote:
>> From: Michael D <michael.j.dilmore@xxxxxxxxx>
>> 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.


-Jay Vosburgh, jay.vosburgh@xxxxxxxxxxxxx