Date: Sun, 6 Aug 2006 01:11:40 +0400 From: Yar Tikhiy <yar@comp.chem.msu.su> To: Sam Leffler <sam@errno.com> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/net if_vlan.c Message-ID: <20060805211140.GG29277@comp.chem.msu.su> In-Reply-To: <44D3758C.1000609@errno.com> References: <200608030959.k739x9N6007207@repoman.freebsd.org> <44D22E2F.4070307@errno.com> <20060803180854.GI97316@comp.chem.msu.su> <44D3758C.1000609@errno.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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 > circumstances). 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. -- Yar
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20060805211140.GG29277>