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Date: Sat, 25 Sep 2004 12:07:00 +0900
Message-ID: <m2hdpnf3mz.wl@minion.local.neville-neil.com>
From: "George V. Neville-Neil" <gnn@neville-neil.com>
To: ming fu <fming@borderware.com>
In-Reply-To: <41541355.50800@borderware.com>
References: <41541355.50800@borderware.com>
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cc: freebsd-net@freebsd.org
Subject: Re: promisc coding question
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At Fri, 24 Sep 2004 08:30:13 -0400,
ming fu wrote:
> 
> Hi,
> 
> in if.h
> #define    IFF_PROMISC    0x100        /* receive all packets */
> #define    IFF_PPROMISC    0x20000        /* user-requested promisc mode */
> 
> Do I have to set both on for the promisc to work?
> If I only need one of them, then what is the difference?
> 

The first flag (IFF_PROMISC) is the one that the kernel code uses and
sets on an interface's ifp structure.  The second one is the one that
comes from user space programs and is sent to the routine ifhwioctl()
to set the first flag.

Having reviewed this flags usage I believe that there are at least two
bugs in the kernel related to its handling:

I beleieve it is only used correctly at:

if.c[1160]                if (new_flags & IFF_PPROMISC) {

but that at:

if.c[1478]                if (ifp->if_flags & IFF_PPROMISC) {

and

if_ethersubr.c[664]                 && (ifp->if_flags & IFF_PPROMISC)== 0) {

neither of those checks can ever succeed because I can find nowhere in
the code that the IFF_PPROMISCx flag is set on an interface.  I suggest
two changes to remedy this:

1) Change IFF_PPROMISC to IFF_USERPROMISC to disambiguate the names.

2) Change if.c[1478] and if_ethersubr.c[664] to check for the correct
   flag, IFF_PROMISC.


Or, someone can tell me that I'm wrong :-)

I will send out a patch next.

Later,
George