LocalIP: consider preferred source address when retrieving default route

src/common/netif/netif.c

@@ -7,15 +7,18 @@
     #include <iphlpapi.h>
 #endif
 
-bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex);
+bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr);
 enum { IF_INDEX_UNINITIALIZED = (uint32_t) -1, IF_INDEX_INVALID = (uint32_t) -2 };
 static uint32_t ifIndex = IF_INDEX_UNINITIALIZED;
 static char ifName[IF_NAMESIZE + 1];
+static uint32_t preferredSourceAddr = 0;
 
 static inline void init()
 {
-    if (ifIndex == (uint32_t) IF_INDEX_UNINITIALIZED && !ffNetifGetDefaultRouteImpl(ifName, &ifIndex))
-        ifIndex = (uint32_t) IF_INDEX_INVALID;
+    if (ifIndex == (uint32_t) IF_INDEX_UNINITIALIZED) {
+        if (!ffNetifGetDefaultRouteImpl(ifName, &ifIndex, &preferredSourceAddr))
+            ifIndex = (uint32_t) IF_INDEX_INVALID;
+    }
 }
 
 const char* ffNetifGetDefaultRouteIfName()
@@ -29,3 +32,9 @@ uint32_t ffNetifGetDefaultRouteIfIndex()
     init();
     return ifIndex;
 }
+
+uint32_t ffNetifGetDefaultRoutePreferredSourceAddr()
+{
+    init();
+    return preferredSourceAddr;
+}

src/common/netif/netif.h

@@ -4,3 +4,4 @@
 
 const char* ffNetifGetDefaultRouteIfName();
 uint32_t ffNetifGetDefaultRouteIfIndex();
+uint32_t ffNetifGetDefaultRoutePreferredSourceAddr();

src/common/netif/netif_bsd.c

@@ -50,7 +50,7 @@ get_rt_address(struct rt_msghdr *rtm, int desired)
     return NULL;
 }
 
-bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
+bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr)
 {
     #if defined(__OpenBSD__) || defined(__DragonFly__)
     int mib[6] = {CTL_NET, PF_ROUTE, 0, AF_INET, NET_RT_FLAGS, RTF_GATEWAY};
@@ -80,6 +80,12 @@ bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
                 memcpy(iface, sdl->sdl_data, sdl->sdl_nlen);
                 iface[sdl->sdl_nlen] = '\0';
                 *ifIndex = sdl->sdl_index;
+
+                // Get the preferred source address
+                struct sockaddr_in* src = (struct sockaddr_in*)get_rt_address(rtm, RTA_IFA);
+                if (preferredSourceAddr && src && src->sin_family == AF_INET)
+                    *preferredSourceAddr = src->sin_addr.s_addr;
+
                 return true;
             }
         }
@@ -108,7 +114,7 @@ bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
             .rtm_type = RTM_GET,
             .rtm_flags = RTF_UP | RTF_GATEWAY,
             .rtm_version = RTM_VERSION,
-            .rtm_addrs = RTA_DST | RTA_IFP,
+            .rtm_addrs = RTA_DST | RTA_IFP | RTA_IFA,
             .rtm_msglen = sizeof(rtmsg.hdr) + sizeof(rtmsg.dst),
             .rtm_pid = pid,
             .rtm_seq = 1,
@@ -139,6 +145,12 @@ bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
                 memcpy(iface, sdl->sdl_data, sdl->sdl_nlen);
                 iface[sdl->sdl_nlen] = '\0';
                 *ifIndex = sdl->sdl_index;
+
+                // Get the preferred source address
+                struct sockaddr_in* src = (struct sockaddr_in*)get_rt_address(&rtmsg.hdr, RTA_IFA);
+                if (preferredSourceAddr && src && src->sin_family == AF_INET)
+                    *preferredSourceAddr = src->sin_addr.s_addr;
+
                 return true;
             }
             return false;

src/common/netif/netif_haiku.c

@@ -11,7 +11,7 @@
 
 // loosely based on Haiku's src/bin/network/route/route.cpp
 
-bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
+bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr)
 {
     // TODO: AF_INET6
     FF_AUTO_CLOSE_FD int pfRoute = socket(AF_INET, SOCK_RAW, AF_INET);

src/common/netif/netif_linux.c

@@ -1,27 +1,176 @@
 #include "netif.h"
 #include "common/io/io.h"
+#include "util/mallocHelper.h"
 
+#include <arpa/inet.h>
+#include <linux/rtnetlink.h>
 #include <net/if.h>
-#include <stdio.h>
 
 #define FF_STR_INDIR(x) #x
 #define FF_STR(x) FF_STR_INDIR(x)
 
-static bool getDefaultRouteIPv4(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
+struct req_t {
+    struct nlmsghdr nlh;
+    struct rtmsg rtm;
+    struct rtattr rta;
+    uint32_t table;
+};
+
+struct Route4Entry {
+    uint32_t dest;
+    uint32_t gateway;
+    uint32_t src;
+    uint8_t prefix_length;
+    uint32_t metric;
+    uint32_t ifindex;
+};
+
+static bool getDefaultRouteIPv4(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr)
 {
-    FILE* FF_AUTO_CLOSE_FILE netRoute = fopen("/proc/net/route", "r");
-    if (!netRoute) return false;
+    FF_AUTO_CLOSE_FD int sock_fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
+    if (sock_fd < 0)
+        return false;
 
-    // skip first line
-    FF_UNUSED(fscanf(netRoute, "%*[^\n]\n"));
+    // Bind socket
+    struct sockaddr_nl addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.nl_family = AF_NETLINK;
+    addr.nl_pid = 0;  // Let kernel assign PID
+    addr.nl_groups = 0;
 
-    unsigned long long destination; //, gateway, flags, refCount, use, metric, mask, mtu, ...
-    while (fscanf(netRoute, "%" FF_STR(IF_NAMESIZE) "s%llx%*[^\n]", iface, &destination) == 2)
-    {
-        if (destination != 0) continue;
-        *ifIndex = if_nametoindex(iface);
+    if (bind(sock_fd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
+        return false;
+    }
+
+    struct req_t req;
+    memset(&req, 0, sizeof(req));
+
+    // Netlink message header
+    req.nlh.nlmsg_len = sizeof(req);
+    req.nlh.nlmsg_type = RTM_GETROUTE;
+    req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+    req.nlh.nlmsg_seq = 0;
+    req.nlh.nlmsg_pid = 0;
+
+    // Route message
+    req.rtm.rtm_family = AF_INET;
+    req.rtm.rtm_dst_len = 0;
+    req.rtm.rtm_src_len = 0;
+    req.rtm.rtm_tos = 0;
+    req.rtm.rtm_table = RT_TABLE_UNSPEC;
+    req.rtm.rtm_protocol = RTPROT_UNSPEC;
+    req.rtm.rtm_scope = RT_SCOPE_UNIVERSE;
+    req.rtm.rtm_type = RTN_UNSPEC;
+    req.rtm.rtm_flags = 0;
+
+    // Route attribute for main table
+    req.rta.rta_len = RTA_LENGTH(sizeof(uint32_t));
+    req.rta.rta_type = RTA_TABLE;
+    req.table = RT_TABLE_MAIN;
+
+    struct sockaddr_nl dest_addr;
+    memset(&dest_addr, 0, sizeof(dest_addr));
+    dest_addr.nl_family = AF_NETLINK;
+    dest_addr.nl_pid = 0;
+    dest_addr.nl_groups = 0;
+
+    ssize_t sent = sendto(sock_fd, &req, sizeof(req), 0,
+                          (struct sockaddr*)&dest_addr, sizeof(dest_addr));
+
+    if (sent != sizeof(req)) {
+        return false;
+    }
+
+    struct sockaddr_nl src_addr;
+    socklen_t src_addr_len = sizeof(src_addr);
+    struct iovec iov = {NULL, 0};
+    struct msghdr msg;
+
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_name = &src_addr;
+    msg.msg_namelen = sizeof(src_addr);
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+
+    ssize_t peek_size = recvmsg(sock_fd, &msg, MSG_PEEK | MSG_TRUNC);
+    if (peek_size < 0) {
+        return false;
+    }
+
+    FF_AUTO_FREE uint8_t* buffer = malloc((size_t)peek_size);
+
+    ssize_t received = recvfrom(sock_fd, buffer, (size_t)peek_size, 0,
+                                (struct sockaddr*)&src_addr, &src_addr_len);
+
+    struct Route4Entry best_gw;
+    memset(&best_gw, 0, sizeof(best_gw));
+
+    for (const struct nlmsghdr* nlh = (struct nlmsghdr*)buffer;
+        NLMSG_OK(nlh, received);
+        nlh = NLMSG_NEXT(nlh, received)) {
+
+        if (nlh->nlmsg_type == NLMSG_DONE)
+            break;
+
+        if (nlh->nlmsg_type != RTM_NEWROUTE)
+            continue;
+
+        struct rtmsg* rtm = (struct rtmsg*)NLMSG_DATA(nlh);
+        if (rtm->rtm_family != AF_INET)
+            continue;
+
+        struct Route4Entry entry;
+        memset(&entry, 0, sizeof(struct Route4Entry));
+        entry.prefix_length = rtm->rtm_dst_len;
+
+        // Parse route attributes
+        uint64_t rtm_len = RTM_PAYLOAD(nlh);
+        for (struct rtattr* rta = RTM_RTA(rtm);
+            RTA_OK(rta, rtm_len);
+            rta = RTA_NEXT(rta, rtm_len)) {
+
+            switch (rta->rta_type) {
+                case RTA_DST:
+                    entry.dest = *(uint32_t*)RTA_DATA(rta);
+                    break;
+                case RTA_GATEWAY:
+                    entry.gateway = *(uint32_t*)RTA_DATA(rta);
+                    break;
+                case RTA_PREFSRC:
+                    entry.src = *(uint32_t*)RTA_DATA(rta);
+                    break;
+                case RTA_PRIORITY:
+                    entry.metric = *(uint32_t*)RTA_DATA(rta);
+                    break;
+                case RTA_OIF:
+                    entry.ifindex = *(uint32_t*)RTA_DATA(rta);
+                    break;
+            }
+        }
+
+        if (entry.gateway == 0 || entry.dest != 0 || entry.prefix_length != 0)
+            continue;
+
+        if (best_gw.gateway == 0 || entry.metric < best_gw.metric) {
+            memcpy(&best_gw, &entry, sizeof(struct Route4Entry));
+        }
+    }
+
+    if (best_gw.gateway != 0) {
+        if (ifIndex) {
+            *ifIndex = best_gw.ifindex;
+        }
+        if (iface) {
+            if (if_indextoname(best_gw.ifindex, iface) == NULL) {
+                iface[0] = '\0';
+            }
+        }
+        if (preferredSourceAddr) {
+            *preferredSourceAddr = best_gw.src;
+        }
         return true;
     }
+
     iface[0] = '\0';
     return false;
 }
@@ -43,9 +192,9 @@ static bool getDefaultRouteIPv6(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
     return false;
 }
 
-bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
+bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr)
 {
-    if (getDefaultRouteIPv4(iface, ifIndex))
+    if (getDefaultRouteIPv4(iface, ifIndex, preferredSourceAddr))
         return true;
 
     return getDefaultRouteIPv6(iface, ifIndex);

src/common/netif/netif_windows.c

@@ -4,7 +4,7 @@
 #include <ws2tcpip.h> // AF_INET6, IN6_IS_ADDR_UNSPECIFIED
 #include <iphlpapi.h>
 
-bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex)
+bool ffNetifGetDefaultRouteImpl(char iface[IF_NAMESIZE + 1], uint32_t* ifIndex, uint32_t* preferredSourceAddr)
 {
     PMIB_IPFORWARD_TABLE2 pIpForwardTable = NULL;
 

src/detection/localip/localip_linux.c

@@ -136,6 +136,7 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
         return "getifaddrs(&ifAddrStruct) failed";
 
     const char* defaultRouteIfName = ffNetifGetDefaultRouteIfName();
+    const uint32_t preferredSourceAddr = ffNetifGetDefaultRoutePreferredSourceAddr();
 
     for (struct ifaddrs* ifa = ifAddrStruct; ifa; ifa = ifa->ifa_next)
     {
@@ -146,8 +147,8 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
             continue;
 #endif
 
-        bool isDefaultRoute = ffStrEquals(defaultRouteIfName, ifa->ifa_name);
-        if ((options->showType & FF_LOCALIP_TYPE_DEFAULT_ROUTE_ONLY_BIT) && !isDefaultRoute)
+        bool isDefaultRouteIf = ffStrEquals(defaultRouteIfName, ifa->ifa_name);
+        if ((options->showType & FF_LOCALIP_TYPE_DEFAULT_ROUTE_ONLY_BIT) && !isDefaultRouteIf)
             continue;
 
         if ((ifa->ifa_flags & IFF_LOOPBACK) && !(options->showType & FF_LOCALIP_TYPE_LOOP_BIT))
@@ -164,6 +165,11 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
                 continue;
 
             struct sockaddr_in* ipv4 = (struct sockaddr_in*) ifa->ifa_addr;
+
+            bool isDefaultRoute = isDefaultRouteIf && (preferredSourceAddr == 0 || ipv4->sin_addr.s_addr == preferredSourceAddr);
+            if ((options->showType & FF_LOCALIP_TYPE_DEFAULT_ROUTE_ONLY_BIT) && !isDefaultRoute)
+                continue;
+
             char addressBuffer[INET_ADDRSTRLEN + 16];
             inet_ntop(AF_INET, &ipv4->sin_addr, addressBuffer, INET_ADDRSTRLEN);
 
@@ -203,7 +209,7 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
                 }
             }
 
-            addNewIp(results, ifa->ifa_name, addressBuffer, AF_INET6, isDefaultRoute, flags, !(options->showType & FF_LOCALIP_TYPE_ALL_IPS_BIT));
+            addNewIp(results, ifa->ifa_name, addressBuffer, AF_INET6, isDefaultRouteIf, flags, !(options->showType & FF_LOCALIP_TYPE_ALL_IPS_BIT));
         }
         #if __FreeBSD__ || __OpenBSD__ || __APPLE__ || __NetBSD__ || __HAIKU__
         else if (ifa->ifa_addr->sa_family == AF_LINK)
@@ -215,7 +221,7 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
             uint8_t* ptr = (uint8_t*) LLADDR((struct sockaddr_dl *)ifa->ifa_addr);
             snprintf(addressBuffer, ARRAY_SIZE(addressBuffer), "%02x:%02x:%02x:%02x:%02x:%02x",
                         ptr[0], ptr[1], ptr[2], ptr[3], ptr[4], ptr[5]);
-            addNewIp(results, ifa->ifa_name, addressBuffer, -1, isDefaultRoute, flags, false);
+            addNewIp(results, ifa->ifa_name, addressBuffer, -1, isDefaultRouteIf, flags, false);
         }
         #else
         else if (ifa->ifa_addr->sa_family == AF_PACKET)
@@ -227,7 +233,7 @@ const char* ffDetectLocalIps(const FFLocalIpOptions* options, FFlist* results)
             uint8_t* ptr = ((struct sockaddr_ll *)ifa->ifa_addr)->sll_addr;
             snprintf(addressBuffer, ARRAY_SIZE(addressBuffer), "%02x:%02x:%02x:%02x:%02x:%02x",
                         ptr[0], ptr[1], ptr[2], ptr[3], ptr[4], ptr[5]);
-            addNewIp(results, ifa->ifa_name, addressBuffer, -1, isDefaultRoute, flags, false);
+            addNewIp(results, ifa->ifa_name, addressBuffer, -1, isDefaultRouteIf, flags, false);
         }
         #endif
     }