From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=iFzU/SFw; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by passt.top (Postfix) with ESMTPS id 5B9445A061B for ; Sat, 27 Sep 2025 21:25:37 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759001136; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cg/58dWO/3h5HndOPUbqytrzbQJvRu88mzNICdtnOZw=; b=iFzU/SFwuJaqjaH2wA+4B8+V+QuKgWEma0m8c6y3HraQ47XvHBwbhTeXXnoKCH78TjxRiP ZwpANjHiLXYwyI5UAPCggVAeqgH0onrNaTSa/j1mc+J3d93tCBMdZY4zAE7gO3EW5xWZJv 6WsebEX4ROatlWHVZh+utm7dTwfbuFY= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-376-hRhjGpc2Oji1RDodt3Vl0Q-1; Sat, 27 Sep 2025 15:25:32 -0400 X-MC-Unique: hRhjGpc2Oji1RDodt3Vl0Q-1 X-Mimecast-MFC-AGG-ID: hRhjGpc2Oji1RDodt3Vl0Q_1759001131 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CEFBF19560A2; Sat, 27 Sep 2025 19:25:31 +0000 (UTC) Received: from jmaloy-thinkpadp16vgen1.rmtcaqc.csb (unknown [10.22.88.36]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id BA63630001A4; Sat, 27 Sep 2025 19:25:30 +0000 (UTC) From: Jon Maloy To: sbrivio@redhat.com, dgibson@redhat.com, david@gibson.dropbear.id.au, jmaloy@redhat.com, passt-dev@passt.top Subject: [PATCH v11 3/9] arp/ndp: send gratuitous ARP / unsolicitated NA when MAC cache entry added Date: Sat, 27 Sep 2025 15:25:16 -0400 Message-ID: <20250927192522.3024554-4-jmaloy@redhat.com> In-Reply-To: <20250927192522.3024554-1-jmaloy@redhat.com> References: <20250927192522.3024554-1-jmaloy@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: C8bLTUdng6mllNWxWlcwhfkMIqIIswNd-Ve_PRNkOHY_1759001131 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: RV5M2ZXFUGMMPU76NMN7UXQEPMTCQOBH X-Message-ID-Hash: RV5M2ZXFUGMMPU76NMN7UXQEPMTCQOBH X-MailFrom: jmaloy@redhat.com 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 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: Gratuitious ARP and unsolicitated NA should be handled with caution because of the risk of malignant users emitting them to disturb network communication. 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. When sending this type of messages, we notice that the guest accepts the update, but also 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. This commit adds this functionality. Signed-off-by: Jon Maloy --- v10: -Made small changes based of feedback from David G. v11: -Moved from 'Gratuitous ARP reply' model to 'ARP Announcement' model. --- arp.c | 41 +++++++++++++++++++++++++++++++++++++++++ arp.h | 2 ++ fwd.c | 8 ++++++++ ndp.c | 10 ++++++++++ ndp.h | 1 + 5 files changed, 62 insertions(+) diff --git a/arp.c b/arp.c index ad088b1..57e7b59 100644 --- a/arp.c +++ b/arp.c @@ -146,3 +146,44 @@ 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_send_gratuitous() - Send a gratuitous 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_send_gratuitous(const struct ctx *c, struct in_addr *ip, + const unsigned char *mac) +{ + char ip_str[INET_ADDRSTRLEN]; + struct { + struct ethhdr eh; + struct arphdr ah; + struct arpmsg am; + } __attribute__((__packed__)) annc; + + /* Ethernet header */ + annc.eh.h_proto = 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 = htons(ARPOP_REQUEST); + annc.ah.ar_hrd = htons(ARPHRD_ETHER); + annc.ah.ar_pro = htons(ETH_P_IP); + annc.ah.ar_hln = ETH_ALEN; + annc.ah.ar_pln = 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)); + + inet_ntop(AF_INET, ip, ip_str, sizeof(ip_str)); + debug("Sending ARP announcement for %s", ip_str); + + tap_send_single(c, &annc, sizeof(annc)); +} + diff --git a/arp.h b/arp.h index d5ad0e1..2cf1326 100644 --- a/arp.h +++ b/arp.h @@ -22,5 +22,7 @@ struct arpmsg { int arp(const struct ctx *c, struct iov_tail *data); void arp_send_init_req(const struct ctx *c); +void arp_send_gratuitous(const struct ctx *c, struct in_addr *ip, + const unsigned char *mac); #endif /* ARP_H */ diff --git a/fwd.c b/fwd.c index 2fd6cee..7f38b40 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" /* Empheral port range: values from RFC 6335 */ static in_port_t fwd_ephemeral_min = (1 << 15) + (1 << 14); @@ -131,6 +133,12 @@ void fwd_neigh_table_update(const struct ctx *c, memcpy(&e->addr, addr, sizeof(*addr)); memcpy(e->mac, mac, ETH_ALEN); + + /* Send gratuitous ARP / unsolicited NA for the new mapping */ + if (inany_v4(addr)) + arp_send_gratuitous(c, inany_v4(addr), e->mac); + else + ndp_send_unsolicited_na(c, &addr->a6); } /** diff --git a/ndp.c b/ndp.c index 588b48f..d7f64a3 100644 --- a/ndp.c +++ b/ndp.c @@ -218,6 +218,16 @@ static void ndp_na(const struct ctx *c, const struct in6_addr *dst, ndp_send(c, dst, &na, sizeof(na)); } +/** + * ndp_send_unsolicited_na() - Send unsolicited NA + * @c: Execution context + * @addr: IPv6 address to advertise + */ +void ndp_send_unsolicited_na(const struct ctx *c, const struct in6_addr *addr) +{ + ndp_na(c, &in6addr_ll_all_nodes, addr); +} + /** * ndp_ra() - Send an NDP Router Advertisement (RA) message * @c: Execution context diff --git a/ndp.h b/ndp.h index 781ea86..320009c 100644 --- a/ndp.h +++ b/ndp.h @@ -12,5 +12,6 @@ int ndp(const struct ctx *c, const struct in6_addr *saddr, struct iov_tail *data); void ndp_timer(const struct ctx *c, const struct timespec *now); void ndp_send_init_req(const struct ctx *c); +void ndp_send_unsolicited_na(const struct ctx *c, const struct in6_addr *addr); #endif /* NDP_H */ -- 2.50.1