Date: Thu, 3 Aug 2006 14:58:00 -0400 From: John Baldwin <jhb@freebsd.org> To: Yar Tikhiy <yar@comp.chem.msu.su> 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: <200608031458.01134.jhb@freebsd.org> In-Reply-To: <20060803180854.GI97316@comp.chem.msu.su> References: <200608030959.k739x9N6007207@repoman.freebsd.org> <44D22E2F.4070307@errno.com> <20060803180854.GI97316@comp.chem.msu.su>
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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. :) -- John Baldwin
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