cvs commit: src/sys/net if_vlan.c

[Yar Tikhiy]

On Thu, Aug 03, 2006 at 02:58:00PM -0400, John Baldwin wrote:
> On Thursday 03 August 2006 14:08, Yar Tikhiy wrote:
> > On Thu, Aug 03, 2006 at 10:11:11AM -0700, Sam Leffler wrote:
> > > Yar Tikhiy wrote:
> > > > yar         2006-08-03 09:59:09 UTC
> > > > 
> > > >   FreeBSD src repository
> > > > 
> > > >   Modified files:
> > > >     sys/net              if_vlan.c 
> > > >   Log:
> > > >   Should vlan_input() ever be called with ifp pointing to a non-Ethernet
> > > >   interface, do not just assign -1 to tag because it breaks the logic of
> > > >   the code to follow.  The better way is to handle this case as an 
> unsupported
> > > >   protocol and return unless INVARIANTS is in effect and we can panic.
> > > >   Panic is good there because the scenario can happen only because of a
> > > >   coding error elsewhere.
> > > >   
> > > >   We also should show the interface name in the panic message for easier
> > > >   debugging of the problem, should it ever emerge.
> > > 
> > > Introducing a panic in a place where you can trivially recover is bad
> > > regardless of why you got there.  Many people run production systems
> > > with INVARIANTS turned on.  Is it now possible to send a "packet of
> > > death" by exploiting this code path?
> > 
> > No nastygram can ever achieve this; only FreeBSD commiters possess
> > the ability to :-)
> > 
> > The panic can never be reached unless one manages to attach a vlan
> > interface to a non-Ethernet physical interface in advance, which
> > is totally prohibited by the code at the beginning of vlan_config();
> > and vlan_config() is the only way to attach a vlan interface to a
> > physical interface.
> > 
> > I.e., it will take a developer breaking the logic in /sys/net to
> > make the code path expoloitable.
> > 
> > OTOH, you are right that we can at least attempt to recover from
> > the situation.  Perhaps it's time to introduce a common macro or
> > function that emits a message on the console and then just calls
> > kdb_backtrace() instead of dumping core and halting the system?
> > So users will be able to post the stack traces to the lists and
> > thus help to spot the possible bugs w/o having to go through panics.
> > I'm unsure if sticking raw kdb_backtrace() calls in such places
> > is a good idea, so I'm suggesting a wrapper function or macro.
> > It is to be used in "can absolutely never happen" cases that are
> > not fatal, like the one under discussion.
> 
> kdb_backtrace() is the wrapper function around other internals. :)

Of course, we can always grep /sys for its usage later ;-)

Just noticed that many calls to kdb_backtrace() are under "#ifdef
KDB" while subr_kdb.c is marked as standard in /sys/conf/files and
the function itself is always available (yet can do nothing.)

Should calls to kdb_backtrace() be put under "#ifdef KDB"?  If they
should, it can justify introducing the combined printf+trace function.

Thanks!

-- 
Yar