From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202510 header.b=yJwTxpvS; dkim-atps=neutral Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by passt.top (Postfix) with ESMTPS id A7DE35A061A for ; Wed, 08 Oct 2025 02:39:00 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202510; t=1759883936; bh=nXNO6RQDfWG7pdgn8ETZl6W6P4hUfjc4pcM3ZIHPCYI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=yJwTxpvSQJ1DmLRkPrr9cXC9xwGRZFyrbldYsXIUTjYBI+J229/hxsU400DrSHmf3 iifdIKNzu2eWijwR1ekgf9VkhdiZLOhL27Z9yuRNqMFbfWBuARHre/TvckpqGvj44n Wkcwv6b7THY2RgMOsjvIE6ZPLcipFqH1+dR9WV3vmnpXQZNf+WMkFLbGIJxbN5m+aY CwkHwezqDNVc736uMUx0Im+6d8PAUJKC++vr8x/ST32ds4/NeIyoOQ9if/N9UhB/HZ zxdYumRM7qYvchyKr7GCQHozZd+O6SfH6hOteCQyaDseAWrmR4LxnrOZb2/PNDIifG +pRDBF2YTaIXA== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4chDdr73dnz4wCl; Wed, 8 Oct 2025 11:38:56 +1100 (AEDT) Date: Wed, 8 Oct 2025 11:27:32 +1100 From: David Gibson To: Stefano Brivio Subject: Re: [PATCH v12 3/9] arp/ndp: send ARP announcement / unsolicited NA when neigbour entry added Message-ID: References: <20251003003412.588801-1-jmaloy@redhat.com> <20251003003412.588801-4-jmaloy@redhat.com> <20251007121022.353a44fc@elisabeth> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="zWSDwLJTYGnIidwR" Content-Disposition: inline In-Reply-To: <20251007121022.353a44fc@elisabeth> Message-ID-Hash: Q5ECCRFPOK4JCE6NLDO3ZIQ3JTK77V7T X-Message-ID-Hash: Q5ECCRFPOK4JCE6NLDO3ZIQ3JTK77V7T X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Jon Maloy , dgibson@redhat.com, passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --zWSDwLJTYGnIidwR Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Oct 07, 2025 at 12:10:22PM +0200, Stefano Brivio wrote: > On Fri, 3 Oct 2025 14:41:56 +1000 > David Gibson wrote: >=20 > > On Thu, Oct 02, 2025 at 08:34:06PM -0400, Jon Maloy wrote: > > > ARP announcements and unsolicited NAs should be handled with caution > > > because of the risk of malignant users emitting them to disturb > > > network communication. > > >=20 > > > There is however one case we where we know it is legitimate > > > and safe for us to send out such messages: The one time we switch > > > from using ctx->own_tap_mac to a MAC address received via the > > > recently added neigbour subscription function. Later changes to > > > the MAC address of a host in an existing entry cannot be fully > > > trusted, so we abstain from doing it in such cases. > > >=20 > > > When sending this type of messages, we notice that the guest accepts > > > the update, but shortly later asks for a confirmation in the form of > > > a regular ARP/NS request. This is responded to with the new value, > > > and we have exactly the effect we wanted. > > >=20 > > > This commit adds this functionality. > > >=20 > > > Signed-off-by: Jon Maloy > > >=20 > > > --- > > > v10: -Made small changes based of feedback from David G. > > > v11: -Moved from 'Gratuitous ARP reply' model to 'ARP Announcement' > > > model. > > > v12: -Excluding loopback and default GW addresses from the ARP/NA > > > announcement to be sent to the guest > > > --- > > > arp.c | 42 ++++++++++++++++++++++++++++++++++++++++++ > > > arp.h | 2 ++ > > > fwd.c | 16 ++++++++++++++++ > > > ndp.c | 10 ++++++++++ > > > ndp.h | 1 + > > > 5 files changed, 71 insertions(+) > > >=20 > > > diff --git a/arp.c b/arp.c > > > index ad088b1..b08780f 100644 > > > --- a/arp.c > > > +++ b/arp.c > > > @@ -146,3 +146,45 @@ void arp_send_init_req(const struct ctx *c) > > > debug("Sending initial ARP request for guest MAC address"); > > > tap_send_single(c, &req, sizeof(req)); > > > } > > > + > > > +/** > > > + * arp_announce() - Send an ARP announcement for an IPv4 host > > > + * @c: Execution context > > > + * @ip: IPv4 address we announce as owned by @mac > > > + * @mac: MAC address to advertise for @ip > > > + */ > > > +void arp_announce(const struct ctx *c, struct in_addr *ip, > > > + const unsigned char *mac) > > > +{ > > > + char ip_str[INET_ADDRSTRLEN]; > > > + char mac_str[ETH_ADDRSTRLEN]; > > > + struct { > > > + struct ethhdr eh; > > > + struct arphdr ah; > > > + struct arpmsg am; > > > + } __attribute__((__packed__)) annc; > > > + > > > + /* Ethernet header */ > > > + annc.eh.h_proto =3D htons(ETH_P_ARP); > > > + memcpy(annc.eh.h_dest, MAC_BROADCAST, sizeof(annc.eh.h_dest)); > > > + memcpy(annc.eh.h_source, mac, sizeof(annc.eh.h_source)); > > > + > > > + /* ARP header */ > > > + annc.ah.ar_op =3D htons(ARPOP_REQUEST); > > > + annc.ah.ar_hrd =3D htons(ARPHRD_ETHER); > > > + annc.ah.ar_pro =3D htons(ETH_P_IP); > > > + annc.ah.ar_hln =3D ETH_ALEN; > > > + annc.ah.ar_pln =3D 4; > > > + > > > + /* ARP message */ > > > + memcpy(annc.am.sha, mac, sizeof(annc.am.sha)); > > > + memcpy(annc.am.sip, ip, sizeof(annc.am.sip)); > > > + memcpy(annc.am.tha, MAC_BROADCAST, sizeof(annc.am.tha)); > > > + memcpy(annc.am.tip, ip, sizeof(annc.am.tip)); =20 > >=20 > > As noted in several earlier revisions, having sip =3D=3D tip (but with > > different mac addresses) looks odd. Is that what the RFCs say to do > > for ARP announcements? > >=20 > > > + inet_ntop(AF_INET, ip, ip_str, sizeof(ip_str)); > > > + eth_ntop(mac, mac_str, sizeof(mac_str)); > > > + debug("Announcing ARP for %s / %s", ip_str, mac_str); > > > + > > > + tap_send_single(c, &annc, sizeof(annc)); > > > +} > > > diff --git a/arp.h b/arp.h > > > index d5ad0e1..4862e90 100644 > > > --- a/arp.h > > > +++ b/arp.h > > > @@ -22,5 +22,7 @@ struct arpmsg { > > > =20 > > > int arp(const struct ctx *c, struct iov_tail *data); > > > void arp_send_init_req(const struct ctx *c); > > > +void arp_announce(const struct ctx *c, struct in_addr *ip, > > > + const unsigned char *mac); > > > =20 > > > #endif /* ARP_H */ > > > diff --git a/fwd.c b/fwd.c > > > index c34bb1c..ade97c8 100644 > > > --- a/fwd.c > > > +++ b/fwd.c > > > @@ -26,6 +26,8 @@ > > > #include "passt.h" > > > #include "lineread.h" > > > #include "flow_table.h" > > > +#include "arp.h" > > > +#include "ndp.h" > > > =20 > > > /* Empheral port range: values from RFC 6335 */ > > > static in_port_t fwd_ephemeral_min =3D (1 << 15) + (1 << 14); > > > @@ -140,6 +142,20 @@ void fwd_neigh_table_update(const struct ctx *c,= const union inany_addr *addr, > > > =20 > > > memcpy(&e->addr, addr, sizeof(*addr)); > > > memcpy(e->mac, mac, ETH_ALEN); > > > + > > > + if (inany_equals(addr, &inany_loopback4)) > > > + return; > > > + if (inany_equals(addr, &inany_loopback6)) > > > + return; =20 > >=20 > > Since you need these explicit checks anyway, there's not much point to > > the dummy entries you created - you could exit on these addresses > > before even looking up the table. >=20 > I guess those entries make sense if we can drop all these checks as a > result. I think we should be able to. We couldn't in this version, because that might have allowed the entries for loopback to be updated, which is certainly wrong. But it will all need re-examination after moving everything over to guest side addresses which AIUI is the plan for the next spin. --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --zWSDwLJTYGnIidwR Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmjlr/MACgkQzQJF27ox 2Gcugw/7BRocHjPWPvvc0szCDWg0uKKRrpiLki+JgGYKG80+jx8C/lCXJg7S3cCR O76UhayufSD27vjdrYxNS/kK6Shg/llmom4NLaqOtGuwlWWc8SIAFGnrzhEmE4qU +rS8onQJFEqOk8IheHtMcol75K5yqkrfC/4JwKv62rj0oSMsQtSf2oFIVfu8fReG 6+ZR4LIWtZYAY4PuYwV5+Ow0hsfvkUs5gfb1Z+OFNXfYuyHlhenFoHT5efxHW8Dq I1KblDmrk2yPaVNOFcRQIFjGdTP2pcbVisvfZOIQ72CVdzMMNEf7mwPPRjMfq2Y9 G5KfT5n9+n6BwwQeDWEjXrNji8J3Q21UkKlvSTPPGDxYvbwt79Wk8Cx9OtjK2MLc qFJwxeDOagyYuGy5eP6T9aAOGBnAL1jGW4okdJyxZLtfEVFOPx9SEwh/ad+KBYrI hdGCwhEDk4U3wET5YzUpY8PZ1uqUcq5PejApZhrC+Wi8plkp99amRNcmlJn2yCg8 q/MiY3R8WnzvTfuplb20NLDhgyA/rOgMzXCQtb9hquzgWZzE82gpf8tWD5fJExLB X1nHTWYfikPClrDGKUWIRuzL5M9X4HakxMpEVjfqJ2WB2e79b5X5p9HmOOx+rZa5 uuaCJ61h5Ot4rZDRn6ebzpcP7T17MEbIxC3Czg3bFKecWKtYE+o= =X5is -----END PGP SIGNATURE----- --zWSDwLJTYGnIidwR--