implement mgre for tap device

Use MAC addresses with 2e:2e: prefix and IPv4 address.

1 files changed, 98 insertions, 12 deletions

diff --git a/gre.c b/gre.c
index d66fd36..68f155c 100644
--- a/gre.c
+++ b/gre.c
@@ -43,6 +43,7 @@ static int tun;
 static int sock;
 static struct sockaddr_storage remote;
 static size_t remote_len;
+static int remote_any;
 static short type = IFF_TUN;
 static uint8_t mac[6];
 static int foreground;
@@ -59,6 +60,7 @@ static int setnonblock(int fd);
 static int runas(const char *user);
 static int daemonize(void);
 static int inet_addr_storage(const char *cp, struct sockaddr_storage *sp, size_t *sp_len);
+static int is_any(const struct sockaddr_storage *ss);
 
 int main(int argc, char **argv)
 {
@@ -101,15 +103,22 @@ int main(int argc, char **argv)
         }
     }
 
-    if ( (argc - optind) != 3)
+    int optnum = argc - optind;
+
+    if (optnum < 2 || optnum  > 3)
     {
-        printf("usage: %s [-n|--tun|-p|--tap] <tun> remote local\n", argv[0]);
+        printf("usage: %s [-n|--tun|-p|--tap] <tun> [remote] local\n", argv[0]);
         return EXIT_FAILURE;
     }
 
     const char *dev = argv[optind++];
-    const char *remote_opt = argv[optind++];
-    const char *local_opt = argv[optind++];
+    const char *remote_opt = NULL;
+    const char *local_opt = NULL;
+
+    if (optnum == 3)
+        remote_opt = argv[optind++];
+
+    local_opt = argv[optind++];
 
     tun = tun_new(type, dev);
     if (tun < 0)
@@ -139,12 +148,36 @@ int main(int argc, char **argv)
         return EXIT_FAILURE;
     }
 
+    if (!remote_opt)
+    {
+        if (local.ss_family == AF_INET)
+            remote_opt = "0.0.0.0";
+        else
+            remote_opt = "::";
+    }
+
     if (inet_addr_storage(remote_opt, &remote, &remote_len))
     {
         fprintf(stderr, "bad remote address\n");
         return EXIT_FAILURE;
     }
 
+    remote_any = is_any(&remote);
+    if (remote_any)
+    {
+        if (type == IFF_TUN)
+        {
+            fprintf(stderr, "tun required specifying remote\n");
+            return EXIT_FAILURE;
+        }
+
+        if (local.ss_family != AF_INET)
+        {
+            fprintf(stderr, "IPv4 required for mGRE\n");
+            return EXIT_FAILURE;
+        }
+    }
+
     setnonblock(sock);
     setnonblock(tun);
     runas("nobody");
@@ -214,7 +247,7 @@ static void gre_cb(void)
 
     if (res < 0)
     {
-        printf("Failed GRE decode");
+        printf("Failed GRE decode\n");
         return;
     }
 
@@ -318,6 +351,14 @@ static int gre_any(const uint8_t *buf, int n)
 static int tun_cb(void)
 {
     int n;
+    struct sockaddr_storage dest;
+
+    if (!remote_any)
+    {
+        memcpy(&dest, &remote, sizeof(struct sockaddr_storage));
+    } else {
+        memset(&dest, 0, sizeof(struct sockaddr_storage));
+    }
 
     n = read(tun, buf, sizeof(buf));
     if (n < 0)
@@ -330,14 +371,36 @@ static int tun_cb(void)
         return 0;
     }
     uint16_t proto = ntohs(*(uint16_t *)(buf + 2));
-    uint8_t *frame;
+    uint8_t *frame = buf;
+
+    if (remote_any)
+    {
+        printf("%02x:%02x:%02x:%02x:%02x:%02x\n",
+          frame[4 + 0],
+          frame[4 + 1],
+          frame[4 + 2],
+          frame[4 + 3],
+          frame[4 + 4],
+          frame[4 + 5]
+        );
+
+        if (frame[4] != 0x2e || frame[5] != 0x2e)
+        {
+            printf("Bad magic number!\n");
+            return 0;
+        }
 
-    if (type == IFF_TAP)
+        struct sockaddr_in *sin = (struct sockaddr_in *)&dest;
+        sin->sin_family = AF_INET;
+        memcpy(&sin->sin_addr.s_addr, frame + 4 + 2, 4);
+
+        int offset = 2 + 6 + 6;
+        frame += offset;
+        n -= offset;
+    }
+    else if (type == IFF_TAP)
     {
-        frame = buf;
         *(uint16_t*)(frame + 2) = htons(ETH_P_TEB);
-    } else {
-        frame = buf;
     }
 
     frame[0] = 0;
@@ -347,13 +410,20 @@ static int tun_cb(void)
     case ETHERTYPE_IPV6:
         break;
     case ETHERTYPE_ARP:
-        if (type == IFF_TAP)
+        if (type == IFF_TAP && !remote_any)
             break;
         return 0;
     default:
         return 0;
     }
-    sendto(sock, frame, n, 0, (struct sockaddr *)&remote, remote_len);
+
+    if (is_any(&dest))
+    {
+        printf("Remote unset!\n");
+        return -1;
+    }
+
+    sendto(sock, frame, n, 0, (struct sockaddr *)&dest, remote_len);
     return 0;
 }
 
@@ -487,3 +557,19 @@ static int inet_addr_storage(const char *cp, struct sockaddr_storage *sp, size_t
 
     return 0;
 }
+
+static int is_any(const struct sockaddr_storage *ss)
+{
+    switch(ss->ss_family) {
+    case AF_INET: {
+        const struct sockaddr_in *sin = (const struct sockaddr_in*)ss;
+        return sin->sin_addr.s_addr == INADDR_ANY;
+    }
+    case AF_INET6: {
+        const struct sockaddr_in6 *sin6 = (const struct sockaddr_in6*)ss;
+        return !memcmp(&in6addr_any, sin6->sin6_addr.s6_addr, sizeof(struct in6_addr));
+    }
+    default:
+        return -1;
+    }
+}