add gretap support

1 files changed, 73 insertions, 14 deletions

diff --git a/gre.c b/gre.c
index 6ded69d..dff0a99 100644
--- a/gre.c
+++ b/gre.c
@@ -2,7 +2,7 @@
  * gre.c - userspace GRE tunnel
  *
  * Copyright (C) 2015 - 2017, Xiaoxiao <i@pxx.io>
- * Copyright (C) 2019, Mikael Magnusson <mikma@users.sourceforge.net>
+ * Copyright (C) 2019 - 2020, Mikael Magnusson <mikma@users.sourceforge.net>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -21,6 +21,7 @@
 #include <arpa/inet.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <getopt.h>
 #include <linux/if_tun.h>
 #include <net/ethernet.h>
 #include <net/if.h>
@@ -42,6 +43,7 @@ static int tun;
 static int sock;
 static struct sockaddr_storage remote;
 static size_t remote_len;
+static short type = IFF_TUN;
 
 uint8_t buf[4096];
 
@@ -50,7 +52,7 @@ static void gre_ipv4(const uint8_t *buf, int n);
 static void gre_ipv6(const uint8_t *buf, int n, const struct sockaddr_in6 *src);
 static void gre_any(const uint8_t *buf, int n);
 static int tun_cb(void);
-static int tun_new(const char *dev);
+static int tun_new(short type, const char *dev);
 static int setnonblock(int fd);
 static int runas(const char *user);
 static int daemonize(void);
@@ -60,22 +62,59 @@ int main(int argc, char **argv)
 {
     fd_set readset;
 
-    if (argc != 4)
+    while (1)
+    {
+        int option_index = 0;
+        static struct option long_options[] = {
+            {"tun", no_argument, 0,  'n' },
+            {"tap", no_argument, 0,  'p' },
+            {0,     0,           0,  0 }
+        };
+
+        char c = getopt_long(argc, argv, "np",
+                             long_options, &option_index);
+        if (c == -1)
+            break;
+
+        switch (c) {
+        case 'n':
+            printf("tun\n");
+            type = IFF_TUN;
+            break;
+
+        case 'p':
+            printf("tap\n");
+            type = IFF_TAP;
+            break;
+
+        case '?':
+            break;
+
+        default:
+            printf("?? getopt returned character code 0%o ??\n", c);
+        }
+    }
+
+    if ( (argc - optind) != 3)
     {
-        printf("usage: %s <tun> remote local\n", argv[0]);
+        printf("usage: %s [-n|--tun|-p|--tap] <tun> remote local\n", argv[0]);
         return EXIT_FAILURE;
     }
 
-    tun = tun_new(argv[1]);
+    const char *dev = argv[optind++];
+    const char *remote_opt = argv[optind++];
+    const char *local_opt = argv[optind++];
+
+    tun = tun_new(type, dev);
     if (tun < 0)
     {
-        printf("failed to init tun device\n");
+        printf("failed to init %s device\n", type == IFF_TAP ? "tap" : "tun");
         return EXIT_FAILURE;
     }
 
     struct sockaddr_storage local;
     size_t local_len = 0;
-    if (inet_addr_storage(argv[3], &local, &local_len))
+    if (inet_addr_storage(local_opt, &local, &local_len))
     {
         fprintf(stderr, "bad local address\n");
         return EXIT_FAILURE;
@@ -94,7 +133,7 @@ int main(int argc, char **argv)
         return EXIT_FAILURE;
     }
 
-    if (inet_addr_storage(argv[2], &remote, &remote_len))
+    if (inet_addr_storage(remote_opt, &remote, &remote_len))
     {
         fprintf(stderr, "bad remote address\n");
         return EXIT_FAILURE;
@@ -227,18 +266,38 @@ static int tun_cb(void)
 
         return 0;
     }
-    buf[0] = 0;
-    buf[1] = 0;
     uint16_t proto = ntohs(*(uint16_t *)(buf + 2));
-    if (proto != ETHERTYPE_IP && proto != ETHERTYPE_IPV6)
+    uint8_t *frame;
+
+    if (type == IFF_TAP)
     {
+        size_t ethsize = 6 + 6 + 2;
+        frame = buf + ethsize;
+        n = n - ethsize;
+        frame[2] = buf[2];
+        frame[3] = buf[3];
+    } else {
+        frame = buf;
+    }
+
+    frame[0] = 0;
+    frame[1] = 0;
+    switch (proto) {
+    case ETHERTYPE_IP:
+    case ETHERTYPE_IPV6:
+        break;
+    case ETHERTYPE_ARP:
+        if (type == IFF_TAP)
+            break;
+        return 0;
+    default:
         return 0;
     }
-    sendto(sock, buf, n, 0, (struct sockaddr *)&remote, remote_len);
+    sendto(sock, frame, n, 0, (struct sockaddr *)&remote, remote_len);
     return 0;
 }
 
-static int tun_new(const char *dev)
+static int tun_new(short type, const char *dev)
 {
     struct ifreq ifr;
     int fd, err;
@@ -251,7 +310,7 @@ static int tun_new(const char *dev)
 
     bzero(&ifr, sizeof(struct ifreq));
 
-    ifr.ifr_flags = IFF_TUN;
+    ifr.ifr_flags = type;
     if (*dev != '\0')
     {
         strncpy(ifr.ifr_name, dev, IFNAMSIZ);