Separate local IP address query into a seaprate function
This change moves the local IP address query into its own function.
We then move it after the recvfrom() as the IP address may be stale by
the time recvfrom() returns.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/inarp.c b/inarp.c
index b87bcd8..deb25f3 100644
--- a/inarp.c
+++ b/inarp.c
@@ -110,6 +110,32 @@
return;
}
+static int get_local_ipaddr(int fd, const char *ifname, struct in_addr *addr)
+{
+ struct sockaddr_in *sa;
+ struct ifreq ifreq;
+ int rc;
+
+ memset(&ifreq, 0, sizeof(ifreq));
+ strcpy(ifreq.ifr_name, ifname);
+
+ rc = ioctl(fd, SIOCGIFADDR, &ifreq);
+ if (rc) {
+ warn("Error querying local address for %s", ifname);
+ return -1;
+ }
+
+ if (ifreq.ifr_addr.sa_family != AF_INET) {
+ warnx("Unknown address family %d in address response",
+ ifreq.ifr_addr.sa_family);
+ return -1;
+ }
+
+ sa = (struct sockaddr_in *)&ifreq.ifr_addr;
+ memcpy(addr, &sa->sin_addr, sizeof(*addr));
+ return 0;
+}
+
static void usage(const char *progname)
{
fprintf(stderr, "Usage: %s <interface>\n", progname);
@@ -135,7 +161,7 @@
errx(EXIT_FAILURE, "Interface name '%s' is invalid", ifname);
static unsigned char src_mac[6];
- static struct in_addr src_ip;
+ static struct in_addr local_ip;
int ifindex;
fd = socket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
@@ -167,25 +193,6 @@
static struct arp_packet inarp_resp;
while (1) {
- /* get local ip address */
- memset(&ifreq_buffer, 0x00, sizeof(ifreq_buffer));
- strcpy(ifreq_buffer.ifr_name, ifname);
- ret = ioctl(fd, SIOCGIFADDR, &ifreq_buffer);
- if (ret == -1) {
- sleep(1);
- continue;
- }
-
- if (AF_INET == ifreq_buffer.ifr_addr.sa_family) {
- memcpy(&src_ip, &ifreq_buffer.ifr_addr.sa_data[2],
- sizeof(src_ip));
- } else {
- warnx("Unknown address family %d in request!",
- ifreq_buffer.ifr_addr.sa_family);
- sleep(1);
- continue;
- }
-
memset((void *)&inarp_resp, 0, sizeof inarp_resp);
length = recvfrom(fd, buffer, ETH_ARP_FRAME_LEN, 0, NULL, NULL);
@@ -213,6 +220,12 @@
printf("src ip = %s\n", inet_ntoa(inarp_req->src_ip));
+ ret = get_local_ipaddr(fd, ifname, &local_ip);
+ /* if we don't have a local IP address to send, just drop the
+ * request */
+ if (ret)
+ continue;
+
int fd_1;
fd_1 = socket(AF_PACKET, SOCK_RAW, 0);
if (fd_1 < 0)
@@ -220,7 +233,7 @@
send_result = send_arp_packet(fd_1, ifindex, &inarp_resp,
ARPOP_InREPLY,
inarp_req->dest_mac,
- &src_ip,
+ &local_ip,
inarp_req->src_mac,
&inarp_req->src_ip);
close(fd_1);