cvs commit: src/sys/net if_vlan.c
yar at comp.chem.msu.su
Sat Aug 5 21:11:59 UTC 2006
On Fri, Aug 04, 2006 at 09:27:56AM -0700, Sam Leffler wrote:
> 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.
> It is my experience that problems like the "packet of death" come about
> from (well-meaning) planting of a landmine of this sort followed,
> sometime later, by another person enabling the code path. I work by the
> rule that panic should be used only in places where you have no way to
> recover or recovery is so hard as to be not worthwhile (based on the
Sounds fair! if_vlan.c appears to use quite a few KASSERT's and
panic's in places where it could recover by, e.g., failing the
current operation. I'll revise them.
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