Date: Fri, 4 Aug 2006 11:03:48 +0400 From: Yar Tikhiy <yar@comp.chem.msu.su> To: John Baldwin <jhb@FreeBSD.org> Cc: Sam Leffler <sam@errno.com>, src-committers@FreeBSD.org, cvs-all@FreeBSD.org, cvs-src@FreeBSD.org Subject: Re: cvs commit: src/sys/net if_vlan.c Message-ID: <20060804070348.GR97316@comp.chem.msu.su> In-Reply-To: <200608031458.01134.jhb@freebsd.org> References: <200608030959.k739x9N6007207@repoman.freebsd.org> <44D22E2F.4070307@errno.com> <20060803180854.GI97316@comp.chem.msu.su> <200608031458.01134.jhb@freebsd.org>
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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
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