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

[Michael J Dilmore]

On 21/06/17 23:39, Jay Vosburgh wrote:
> 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.
>
> 	-J
>
> ---
> 	-Jay Vosburgh, jay.vosburgh@xxxxxxxxxxxxx
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?