Re: [PATCH v6 8/8] icmp: let icmp use mac address from flowside structure

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Sep 09, 2025 at 09:59:19PM -0400, Jon Maloy wrote:
> Even ICMP needs to be updated to use the external MAC address instead
> of just the own tap address when applicable. We do that here.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> 
> ---
> v3: - Adapted to the move of external MAC address from struct flowside
>       to struct flow_common
> v4: - Adapted to name changes in previous commits in this series
> v5: - Added conditional lookup in ARP/NDP if the flow's tap_omac is
>       undefined
> v6: - Looking up MAC of ICMP generating node in udp_send_tap_icmp4/6()
>       when available, instead trusting the contents of flow->tap_omac.
> ---
>  icmp.c |  8 ++++++--
>  ndp.c  |  2 +-
>  tap.c  | 10 ++++++----
>  tap.h  |  4 ++--
>  udp.c  | 12 ++++++++++--
>  5 files changed, 25 insertions(+), 11 deletions(-)
> 
> diff --git a/icmp.c b/icmp.c
> index 6dffafb..1d99632 100644
> --- a/icmp.c
> +++ b/icmp.c
> @@ -125,17 +125,21 @@ void icmp_sock_handler(const struct ctx *c, union epoll_ref ref)
>  	flow_dbg(pingf, "echo reply to tap, ID: %"PRIu16", seq: %"PRIu16,
>  		 ini->eport, seq);
>  
> +	/* Try to find true MAC address in ARP/NDP table if needed */
> +	if (MAC_IS_ZERO(pingf->f.tap_omac))
> +		fwd_neigh_mac_get(c, &ini->oaddr, pingf->f.tap_omac);
> +
>  	if (pingf->f.type == FLOW_PING4) {
>  		const struct in_addr *saddr = inany_v4(&ini->oaddr);
>  		const struct in_addr *daddr = inany_v4(&ini->eaddr);
>  
>  		ASSERT(saddr && daddr); /* Must have IPv4 addresses */
> -		tap_icmp4_send(c, *saddr, *daddr, buf, n);
> +		tap_icmp4_send(c, *saddr, *daddr, buf, pingf->f.tap_omac, n);
>  	} else if (pingf->f.type == FLOW_PING6) {
>  		const struct in6_addr *saddr = &ini->oaddr.a6;
>  		const struct in6_addr *daddr = &ini->eaddr.a6;
>  
> -		tap_icmp6_send(c, saddr, daddr, buf, n);
> +		tap_icmp6_send(c, saddr, daddr, buf, pingf->f.tap_omac, n);
>  	}
>  	return;
>  
> diff --git a/ndp.c b/ndp.c
> index 944371c..1e9d0f4 100644
> --- a/ndp.c
> +++ b/ndp.c
> @@ -184,7 +184,7 @@ static void ndp_send(const struct ctx *c, const struct in6_addr *dst,
>  {
>  	const struct in6_addr *src = &c->ip6.our_tap_ll;
>  
> -	tap_icmp6_send(c, src, dst, buf, l4len);
> +	tap_icmp6_send(c, src, dst, buf, c->our_tap_mac, l4len);
>  }
>  
>  /**
> diff --git a/tap.c b/tap.c
> index a390be8..8b10e14 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -277,13 +277,14 @@ void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
>   * @src:	IPv4 source address
>   * @dst:	IPv4 destination address
>   * @in:		ICMP packet, including ICMP header
> + * @src_mac:	MAC address to be used as source for message
>   * @l4len:	ICMP packet length, including ICMP header
>   */
>  void tap_icmp4_send(const struct ctx *c, struct in_addr src, struct in_addr dst,
> -		    const void *in, size_t l4len)
> +		    const void *in, const void *src_mac, size_t l4len)
>  {
>  	char buf[USHRT_MAX];
> -	struct iphdr *ip4h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IP);
> +	struct iphdr *ip4h = tap_push_l2h(c, buf, src_mac, ETH_P_IP);
>  	struct icmphdr *icmp4h = tap_push_ip4h(ip4h, src, dst,
>  					       l4len, IPPROTO_ICMP);
>  
> @@ -384,14 +385,15 @@ void tap_udp6_send(const struct ctx *c,
>   * @src:	IPv6 source address
>   * @dst:	IPv6 destination address
>   * @in:		ICMP packet, including ICMP header
> + * @src_mac:	MAC address to be used as source for message
>   * @l4len:	ICMP packet length, including ICMP header
>   */
>  void tap_icmp6_send(const struct ctx *c,
>  		    const struct in6_addr *src, const struct in6_addr *dst,
> -		    const void *in, size_t l4len)
> +		    const void *in, const void *src_mac, size_t l4len)
>  {
>  	char buf[USHRT_MAX];
> -	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, c->our_tap_mac, ETH_P_IPV6);
> +	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, src_mac, ETH_P_IPV6);
>  	struct icmp6hdr *icmp6h = tap_push_ip6h(ip6h, src, dst, l4len,
>  						IPPROTO_ICMPV6, 0);
>  
> diff --git a/tap.h b/tap.h
> index 02f7761..1864173 100644
> --- a/tap.h
> +++ b/tap.h
> @@ -91,7 +91,7 @@ void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
>  		   struct in_addr dst, in_port_t dport,
>  		   const void *in, size_t dlen);
>  void tap_icmp4_send(const struct ctx *c, struct in_addr src, struct in_addr dst,
> -		    const void *in, size_t l4len);
> +		    const void *in, const void *src_mac, size_t l4len);
>  const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
>  				     const struct in6_addr *src);
>  void *tap_push_ip6h(struct ipv6hdr *ip6h,
> @@ -103,7 +103,7 @@ void tap_udp6_send(const struct ctx *c,
>  		   uint32_t flow, void *in, size_t dlen);
>  void tap_icmp6_send(const struct ctx *c,
>  		    const struct in6_addr *src, const struct in6_addr *dst,
> -		    const void *in, size_t l4len);
> +		    const void *in, const void *src_mac, size_t l4len);
>  void tap_send_single(const struct ctx *c, const void *data, size_t l2len);
>  size_t tap_send_frames(const struct ctx *c, const struct iovec *iov,
>  		       size_t bufs_per_frame, size_t nframes);
> diff --git a/udp.c b/udp.c
> index eb57f05..ff15e37 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -400,6 +400,8 @@ static void udp_send_tap_icmp4(const struct ctx *c,
>  	struct in_addr eaddr = toside->eaddr.v4mapped.a4;
>  	in_port_t eport = toside->eport;
>  	in_port_t oport = toside->oport;
> +	union inany_addr saddr_any;
> +	uint8_t tap_omac[ETH_ALEN];
>  	struct {
>  		struct icmphdr icmp4h;
>  		struct iphdr ip4h;
> @@ -421,7 +423,10 @@ static void udp_send_tap_icmp4(const struct ctx *c,
>  	tap_push_uh4(&msg.uh, eaddr, eport, oaddr, oport, in, dlen);
>  	memcpy(&msg.data, in, dlen);
>  
> -	tap_icmp4_send(c, saddr, eaddr, &msg, msglen);
> +	/* Try to obtain the MAC address of the generating node */
> +	saddr_any = inany_from_v4(saddr);
> +	fwd_neigh_mac_get(c, &saddr_any, tap_omac);
> +	tap_icmp4_send(c, saddr, eaddr, &msg, tap_omac, msglen);
>  }
>  
>  
> @@ -445,6 +450,7 @@ static void udp_send_tap_icmp6(const struct ctx *c,
>  	const struct in6_addr *eaddr = &toside->eaddr.a6;
>  	in_port_t eport = toside->eport;
>  	in_port_t oport = toside->oport;
> +	uint8_t tap_omac[ETH_ALEN];
>  	struct {
>  		struct icmp6_hdr icmp6h;
>  		struct ipv6hdr ip6h;
> @@ -466,7 +472,9 @@ static void udp_send_tap_icmp6(const struct ctx *c,
>  	tap_push_uh6(&msg.uh, eaddr, eport, oaddr, oport, in, dlen);
>  	memcpy(&msg.data, in, dlen);
>  
> -	tap_icmp6_send(c, saddr, eaddr, &msg, msglen);
> +	/* Try to obtain the MAC address of the generating node */
> +	fwd_neigh_mac_get(c, (union inany_addr *) saddr, tap_omac);
> +	tap_icmp6_send(c, saddr, eaddr, &msg, tap_omac, msglen);
>  }
>  
>  /**
> -- 
> 2.50.1
> 

-- 
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

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