[v3] alfred: Request MAC resolution for IPv4 address not in ARP cache

Message ID 20181029175759.20637-1-jhaws@sdl.usu.edu
State Accepted, archived
Commit 5610d5bf8f4447b4d689aede638b4e92ae343340
Delegated to: Simon Wunderlich
Headers
Series [v3] alfred: Request MAC resolution for IPv4 address not in ARP cache |

Commit Message

Jonathan Haws Oct. 29, 2018, 5:57 p.m. UTC
  When using IPv4, if the remote server is not yet in the ARP cache, the
MAC resolution will fail and data appear to not be shared via alfred.
Add a routine (modified from batctl sources) to request MAC resolution
by simply sending a datagram to the discard port (UDP/9). This adds the
remote MAC to the ARP cache, resulting in successful MAC resolution.

Fixes: c7da798113a2 ("alfred: IPv4 multicast distribution support.")
Signed-off-by: Jonathan Haws <jhaws@sdl.usu.edu>
---
 util.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)
  

Comments

gary Nov. 1, 2018, 1:30 a.m. UTC | #1
Tested-by: Gary Zou <guohuizou2000@sina.com>

-----Original Message-----
From: Jonathan Haws <jhaws@sdl.usu.edu> 
Sent: 2018年10月30日 1:58
To: guohuizou2000@sina.com; b.a.t.m.a.n@lists.open-mesh.org
Cc: Jonathan Haws <jhaws@sdl.usu.edu>
Subject: [B.A.T.M.A.N.][PATCH v3] alfred: Request MAC resolution for IPv4
address not in ARP cache


When using IPv4, if the remote server is not yet in the ARP cache, the MAC
resolution will fail and data appear to not be shared via alfred.
Add a routine (modified from batctl sources) to request MAC resolution by
simply sending a datagram to the discard port (UDP/9). This adds the remote
MAC to the ARP cache, resulting in successful MAC resolution.

Fixes: c7da798113a2 ("alfred: IPv4 multicast distribution support.")
Signed-off-by: Jonathan Haws <jhaws@sdl.usu.edu>
---
 util.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/util.c b/util.c
index dd3f00f..0794792 100644
--- a/util.c
+++ b/util.c
@@ -30,6 +30,7 @@
 #include <sys/ioctl.h>
 #include <sys/time.h>
 #include <time.h>
+#include <unistd.h>
 #include "alfred.h"
 
 int time_diff(struct timespec *tv1, struct timespec *tv2, @@ -80,11 +81,35
@@ bool is_valid_ether_addr(uint8_t addr[ETH_ALEN])
 	return true;
 }
 
+static void ipv4_request_mac_resolve(const alfred_addr *addr) {
+	const struct sockaddr *sockaddr;
+	struct sockaddr_in inet4;
+	size_t sockaddr_len;
+	int sock;
+	char t = 0;
+
+	sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (sock < 0)
+		return;
+
+	memset(&inet4, 0, sizeof(inet4));
+	inet4.sin_family = AF_INET;
+	inet4.sin_port = htons(9);
+	inet4.sin_addr.s_addr = addr->ipv4.s_addr;
+	sockaddr = (const struct sockaddr *)&inet4;
+	sockaddr_len = sizeof(inet4);
+
+	sendto(sock, &t, sizeof(t), 0, sockaddr, sockaddr_len);
+	close(sock);
+}
+
 int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,
 		     struct ether_addr *mac)
 {
 	struct arpreq arpreq;
 	struct sockaddr_in *sin;
+	int retries = 1;
 
 	memset(&arpreq, 0, sizeof(arpreq));
 	memset(mac, 0, ETH_ALEN);
@@ -96,8 +121,13 @@ int ipv4_arp_request(struct interface *interface, const
alfred_addr *addr,
 	strncpy(arpreq.arp_dev, interface->interface,
sizeof(arpreq.arp_dev));
 	arpreq.arp_dev[sizeof(arpreq.arp_dev) - 1] = '\0';
 
-	if (ioctl(interface->netsock, SIOCGARP, &arpreq) < 0)
-		return -1;
+	while ((ioctl(interface->netsock, SIOCGARP, &arpreq) < 0) ||
!(arpreq.arp_flags & ATF_COM)) {
+		ipv4_request_mac_resolve(addr);
+		usleep(200000);
+
+		if (retries-- == 0)
+			break;
+	}
 
 	if (arpreq.arp_flags & ATF_COM) {
 		memcpy(mac, arpreq.arp_ha.sa_data, sizeof(*mac));
--
2.17.1
  
Sven Eckelmann Nov. 1, 2018, 6:15 a.m. UTC | #2
On Montag, 29. Oktober 2018 18:57:59 CET Jonathan Haws wrote:
> When using IPv4, if the remote server is not yet in the ARP cache, the
> MAC resolution will fail and data appear to not be shared via alfred.
> Add a routine (modified from batctl sources) to request MAC resolution
> by simply sending a datagram to the discard port (UDP/9). This adds the
> remote MAC to the ARP cache, resulting in successful MAC resolution.
> 
> Fixes: c7da798113a2 ("alfred: IPv4 multicast distribution support.")
> Signed-off-by: Jonathan Haws <jhaws@sdl.usu.edu>
> ---
>  util.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)


Applied as 5610d5bf8f44 [1]

Thanks,
	Sven

[1] https://git.open-mesh.org/alfred.git/commit/5610d5bf8f4447b4d689aede638b4e92ae343340
  

Patch

diff --git a/util.c b/util.c
index dd3f00f..0794792 100644
--- a/util.c
+++ b/util.c
@@ -30,6 +30,7 @@ 
 #include <sys/ioctl.h>
 #include <sys/time.h>
 #include <time.h>
+#include <unistd.h>
 #include "alfred.h"
 
 int time_diff(struct timespec *tv1, struct timespec *tv2,
@@ -80,11 +81,35 @@  bool is_valid_ether_addr(uint8_t addr[ETH_ALEN])
 	return true;
 }
 
+static void ipv4_request_mac_resolve(const alfred_addr *addr)
+{
+	const struct sockaddr *sockaddr;
+	struct sockaddr_in inet4;
+	size_t sockaddr_len;
+	int sock;
+	char t = 0;
+
+	sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (sock < 0)
+		return;
+
+	memset(&inet4, 0, sizeof(inet4));
+	inet4.sin_family = AF_INET;
+	inet4.sin_port = htons(9);
+	inet4.sin_addr.s_addr = addr->ipv4.s_addr;
+	sockaddr = (const struct sockaddr *)&inet4;
+	sockaddr_len = sizeof(inet4);
+
+	sendto(sock, &t, sizeof(t), 0, sockaddr, sockaddr_len);
+	close(sock);
+}
+
 int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,
 		     struct ether_addr *mac)
 {
 	struct arpreq arpreq;
 	struct sockaddr_in *sin;
+	int retries = 1;
 
 	memset(&arpreq, 0, sizeof(arpreq));
 	memset(mac, 0, ETH_ALEN);
@@ -96,8 +121,13 @@  int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,
 	strncpy(arpreq.arp_dev, interface->interface, sizeof(arpreq.arp_dev));
 	arpreq.arp_dev[sizeof(arpreq.arp_dev) - 1] = '\0';
 
-	if (ioctl(interface->netsock, SIOCGARP, &arpreq) < 0)
-		return -1;
+	while ((ioctl(interface->netsock, SIOCGARP, &arpreq) < 0) || !(arpreq.arp_flags & ATF_COM)) {
+		ipv4_request_mac_resolve(addr);
+		usleep(200000);
+
+		if (retries-- == 0)
+			break;
+	}
 
 	if (arpreq.arp_flags & ATF_COM) {
 		memcpy(mac, arpreq.arp_ha.sa_data, sizeof(*mac));