Date: Tue, 30 May 2000 18:19:27 -0700 (PDT) From: Archie Cobbs <archie@whistle.com> To: itojun@iijlab.net Cc: freebsd-net@FreeBSD.ORG Subject: Re: BPF fix to if_loop.c Message-ID: <200005310119.SAA86718@bubba.whistle.com> In-Reply-To: <4814.959735171@coconut.itojun.org> from "itojun@iijlab.net" at "May 31, 2000 10:06:11 am"
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itojun@iijlab.net writes:
> >> sorry this was incorrect. however, I think there should be check
> >> if ifp really wants DLT_NULL encapsulation or not.
> >Hmm.. maybe a better fix is to remove this BPF section altogether.. ?
> >It's only going to result in showing the same packet twice, right?
>
> there are couple of different stories here.
> note that you can pass any ifp to if_simloop().
>
> a. when if_simloop(ifp = lo0), there must be call to bpf_mtap,
> with DLT_NULL encapsulation. if we don't do it here, nobody will.
> b. when if_simloop(ifp = non-lo0), there are two cases.
> b1. if it was called from layer 2 specific code like
> if_ethersubr.c, if_simloop may want to inject the packet
> with no encapsulation change.
> b2. if it was called from ip{6,}_mloopback, if_simloop() must
> not call bpf_mtap. with the current code, ifp_simloop
> injects packet as is (with no layer 2 header) into, for
> example to bpf for ethernet interface, passing junk to bpf
> listeners. this is the problem I experienced.
>
> in case of b1, your description should be correct (seeing same
> packet twice). in case of b2, I'm still not sure how to resolve it.
> maybe I don't get the ultimate goal for this change from 4.4BSD.
The commit comment to revision 1.33 of if_loop.c may be slightly
enlightening..
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/net/if_loop.c
For an example of the resulting cleanup, see:
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/net/if_ethersubr.c.diff?r1=1.48&r2=1.49
Maybe the caller of if_simloop() should be responsible for the BPF part..
-Archie
___________________________________________________________________________
Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
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