From owner-freebsd-net  Tue Nov 26 12:54:26 2002
Delivered-To: freebsd-net@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id D2AA437B401
	for <freebsd-net@freebsd.org>; Tue, 26 Nov 2002 12:54:23 -0800 (PST)
Received: from ns1.interbgc.com (mail.interbgc.com [217.9.224.3])
	by mx1.FreeBSD.org (Postfix) with SMTP id D5EDD43E9C
	for <freebsd-net@freebsd.org>; Tue, 26 Nov 2002 12:54:19 -0800 (PST)
	(envelope-from misho@interbgc.com)
Received: (qmail 63099 invoked by alias); 26 Nov 2002 20:54:02 -0000
Message-ID: <20021126205402.63098.qmail@ns1.interbgc.com>
References: <127338536921.20021126141359@netasq.com>
In-Reply-To: <127338536921.20021126141359@netasq.com> 
From: Mihail Balikov <misho@interbgc.com>
To: Fabien THOMAS <fabien.thomas@netasq.com>
Cc: freebsd-net@freebsd.org
X-Priority: 3
Subject: Re: bpf_tap problem with PKTHDR
Date: Tue, 26 Nov 2002 22:54:02 +0200
Mime-Version: 1.0
Content-Type: text/plain; format=flowed; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-net@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-net.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-net>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-net>
X-Loop: FreeBSD.org

I found similar problem with bpf flag BIOCSSEESENT. Here is simple 
workaround: 

if_ethersubr.c: ether_input() 

       /* Check for a BPF tap */
       if (ifp->if_bpf != NULL) {
               /* This kludge is OK; BPF treats the "mbuf" as read-only */
               struct mbuf m0;

               m0.m_next = m;
               m0.m_data = (char *)eh;
               m0.m_len  = ETHER_HDR_LEN; 

               /* make BOICSSEESENT happy */
               m0.m_pkthdr.rcvif = ifp;
               bpf_mtap(ifp, &m0);
       } 

But there's no reason for such "kludge", if ethernet header is first mbuf. 

regards,
Mihail 


Fabien THOMAS writes: 

> Hi, 
> 
> It seems there is a problem in the bpf_mtap code: 
> 
> Actually the code assume in the seesent case that mbuf will have a pkthdr structure. 
> 
> There is 2 problems here:
>       + they did not check for that with (m_flag & M_PKTHDR)
>       + at the upper level the caller forge fake mbuf that did not
>       contain any pkthdr and did not initialize the m_flags field 
> 
> what do you think about that ?
>       
> if_ethersubr.c case: 
> 
>         /* Check for a BPF tap */
>         if (ifp->if_bpf != NULL) {
>                 struct m_hdr mh; 
> 
>                 /* This kludge is OK; BPF treats the "mbuf" as read-only */
>                 mh.mh_next = m;
>                 mh.mh_data = (char *)eh;
>                 mh.mh_len = ETHER_HDR_LEN;
>                 bpf_mtap(ifp, (struct mbuf *)&mh);
>         } 
> 
> 
> bpf_mtap function:
> /*
>  * Incoming linkage from device drivers, when packet is in an mbuf chain.
>  */
> void
> bpf_mtap(ifp, m)
>         struct ifnet *ifp;
>         struct mbuf *m;
> {
>         struct bpf_if *bp = ifp->if_bpf;
>         struct bpf_d *d;
>         u_int pktlen, slen;
>         struct mbuf *m0; 
> 
>         pktlen = 0;
>         for (m0 = m; m0 != 0; m0 = m0->m_next)
>                 pktlen += m0->m_len; 
> 
>         for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
>                 if (!d->bd_seesent && (m->m_pkthdr.rcvif == NULL))
>                         continue;
>                 ++d->bd_rcount;
>                 slen = bpf_filter(d->bd_filter, (u_char *)m, pktlen, 0);
>                 if (slen != 0)
>                         catchpacket(d, (u_char *)m, pktlen, slen, bpf_mcopy);
>         }
> } 
> 
> fabien
 

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-net" in the body of the message