added GetMask

[ppp.git] / pppd / sys-linux.c

diff --git a/pppd/sys-linux.c b/pppd/sys-linux.c
index 7d203c7a3a8cd0b6a2aafd729cde519b687a9643..34830f06ba0a11e94433b814397e00dd553071b5 100644 (file)
--- a/pppd/sys-linux.c
+++ b/pppd/sys-linux.c
@@ -1147,6 +1147,73 @@ int get_ether_addr (u_int32_t ipaddr, struct sockaddr *hwaddr)
     return 1;
   }
 
+/*
+ * Return user specified netmask, modified by any mask we might determine
+ * for address `addr' (in network byte order).
+ * Here we scan through the system's list of interfaces, looking for
+ * any non-point-to-point interfaces which might appear to be on the same
+ * network as `addr'.  If we find any, we OR in their netmask to the
+ * user-specified netmask.
+ */
+u_int32_t
+GetMask(addr)
+    u_int32_t addr;
+{
+    u_int32_t mask, nmask, ina;
+    struct ifreq *ifr, *ifend, ifreq;
+    struct ifconf ifc;
+    struct ifreq ifs[MAX_IFS];
+
+    addr = ntohl(addr);
+    if (IN_CLASSA(addr))       /* determine network mask for address class */
+       nmask = IN_CLASSA_NET;
+    else if (IN_CLASSB(addr))
+       nmask = IN_CLASSB_NET;
+    else
+       nmask = IN_CLASSC_NET;
+    /* class D nets are disallowed by bad_ip_adrs */
+    mask = netmask | htonl(nmask);
+
+    /*
+     * Scan through the system's network interfaces.
+     */
+    ifc.ifc_len = sizeof(ifs);
+    ifc.ifc_req = ifs;
+    if (ioctl(sockfd, SIOCGIFCONF, &ifc) < 0) {
+       syslog(LOG_WARNING, "ioctl(SIOCGIFCONF): %m");
+       return mask;
+    }
+    ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
+    for (ifr = ifc.ifc_req; ifr < ifend; ifr = (struct ifreq *)
+               ((char *)&ifr->ifr_addr + ifr->ifr_addr.sa_len)) {
+       /*
+        * Check the interface's internet address.
+        */
+       if (ifr->ifr_addr.sa_family != AF_INET)
+           continue;
+       ina = ((struct sockaddr_in *) &ifr->ifr_addr)->sin_addr.s_addr;
+       if ((ntohl(ina) & nmask) != (addr & nmask))
+           continue;
+       /*
+        * Check that the interface is up, and not point-to-point or loopback.
+        */
+       strncpy(ifreq.ifr_name, ifr->ifr_name, sizeof(ifreq.ifr_name));
+       if (ioctl(sockfd, SIOCGIFFLAGS, &ifreq) < 0)
+           continue;
+       if ((ifreq.ifr_flags & (IFF_UP|IFF_POINTOPOINT|IFF_LOOPBACK))
+           != IFF_UP)
+           continue;
+       /*
+        * Get its netmask and OR it into our mask.
+        */
+       if (ioctl(sockfd, SIOCGIFNETMASK, &ifreq) < 0)
+           continue;
+       mask |= ((struct sockaddr_in *)&ifreq.ifr_addr)->sin_addr.s_addr;
+    }
+
+    return mask;
+}
+
 /*
  * Internal routine to decode the version.modification.patch level
  */