From owner-cvs-all@FreeBSD.ORG Thu Aug 3 18:09:13 2006 Return-Path: X-Original-To: cvs-all@FreeBSD.org Delivered-To: cvs-all@FreeBSD.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BACB216A4E1; Thu, 3 Aug 2006 18:09:13 +0000 (UTC) (envelope-from yar@comp.chem.msu.su) Received: from comp.chem.msu.su (comp.chem.msu.su [158.250.32.97]) by mx1.FreeBSD.org (Postfix) with ESMTP id DC54E43D86; Thu, 3 Aug 2006 18:09:04 +0000 (GMT) (envelope-from yar@comp.chem.msu.su) Received: from comp.chem.msu.su (localhost [127.0.0.1]) by comp.chem.msu.su (8.13.4/8.13.3) with ESMTP id k73I8tLL005510; Thu, 3 Aug 2006 22:08:55 +0400 (MSD) (envelope-from yar@comp.chem.msu.su) Received: (from yar@localhost) by comp.chem.msu.su (8.13.4/8.13.3/Submit) id k73I8tqr005509; Thu, 3 Aug 2006 22:08:55 +0400 (MSD) (envelope-from yar) Date: Thu, 3 Aug 2006 22:08:55 +0400 From: Yar Tikhiy To: Sam Leffler Message-ID: <20060803180854.GI97316@comp.chem.msu.su> References: <200608030959.k739x9N6007207@repoman.freebsd.org> <44D22E2F.4070307@errno.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44D22E2F.4070307@errno.com> User-Agent: Mutt/1.5.9i Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/net if_vlan.c X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 03 Aug 2006 18:09:13 -0000 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. -- Yar