Merge pull request #3675 from authmillenon/gnrc_ipv6/fix/check-mtu

gnrc_ipv6: check link MTU before sending

sys/include/net/gnrc/ipv6/netif.h

@@ -28,6 +28,7 @@
 #include "kernel_macros.h"
 #include "kernel_types.h"
 #include "mutex.h"
+#include "net/ipv6.h"
 #include "net/ipv6/addr.h"
 #include "vtimer.h"
 
@@ -51,11 +52,19 @@ extern "C" {
 /**
  * @brief   Default MTU
  *
- * @see <a href="https://tools.ietf.org/html/rfc2460#section-5">
+ * An interface will choose this MTU if the link-layer's maximum packet size
- *          RFC 2460, section 5
+ * (see @ref NETOPT_MAX_PACKET_SIZE) is lesser than the @ref IPV6_MIN_MTU or if it just not
- *      </a>
+ * provide it. For RFC-compatible communication it must be at least @ref IPV6_MIN_MTU.
+ *
+ * @note    If the scenario the node is used in allows for it and the packet size is predictable,
+ *          a user might choose to set @ref GNRC_IPV6_NETIF_DEFAULT_MTU to a lesser value than
+ *          @ref IPV6_MIN_MTU to optimize for code size (e.g. because it is then possible to omit
+ *          @ref net_gnrc_sixlowpan_frag) and memory usage (e.g. because @ref GNRC_PKTBUF_SIZE
+ *          can be much smaller).
  */
-#define GNRC_IPV6_NETIF_DEFAULT_MTU (1280)
+#ifndef GNRC_IPV6_NETIF_DEFAULT_MTU
+#define GNRC_IPV6_NETIF_DEFAULT_MTU (IPV6_MIN_MTU)
+#endif
 
 /**
  * @brief   Default hop limit

sys/include/net/ipv6.h

@@ -32,6 +32,15 @@
 extern "C" {
 #endif
 
+/**
+ * @brief   minimum **M**aximum **T**ransition **U**nit
+ *
+ * @see <a href="https://tools.ietf.org/html/rfc4944#section-5.3">
+ *          RFC 2460, section 5.3
+ *      </a>
+ */
+#define IPV6_MIN_MTU    (1280)
+
 #ifdef __cplusplus
 }
 #endif

sys/net/gnrc/link_layer/netdev_eth/gnrc_netdev_eth.c

@@ -223,7 +223,7 @@ static inline int _get_max_pkt_sz(uint16_t *value, size_t max_len)
         return -EOVERFLOW;
     }
 
-    *value = ETHERNET_MAX_LEN;
+    *value = ETHERNET_DATA_LEN;
 
     return sizeof(uint16_t);
 }

sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c

@@ -11,6 +11,7 @@
  *
  * @file
  */
+#include <assert.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <stdbool.h>
@@ -205,31 +206,29 @@ static void *_event_loop(void *args)
     return NULL;
 }
 
-#ifdef MODULE_GNRC_SIXLOWPAN
 static void _send_to_iface(kernel_pid_t iface, gnrc_pktsnip_t *pkt)
 {
+    ((gnrc_netif_hdr_t *)pkt->data)->if_pid = iface;
     gnrc_ipv6_netif_t *if_entry = gnrc_ipv6_netif_get(iface);
 
-    ((gnrc_netif_hdr_t *)pkt->data)->if_pid = iface;
+    assert(if_entry != NULL);
-
+    if (gnrc_pkt_len(pkt->next) > if_entry->mtu) {
+        DEBUG("ipv6: packet too big\n");
+        gnrc_pktbuf_release(pkt);
+        return;
+    }
+#ifdef MODULE_GNRC_SIXLOWPAN
     if ((if_entry != NULL) && (if_entry->flags & GNRC_IPV6_NETIF_FLAGS_SIXLOWPAN)) {
         DEBUG("ipv6: send to 6LoWPAN instead\n");
         if (!gnrc_netapi_dispatch_send(GNRC_NETTYPE_SIXLOWPAN, GNRC_NETREG_DEMUX_CTX_ALL, pkt)) {
             DEBUG("ipv6: no 6LoWPAN thread found");
             gnrc_pktbuf_release(pkt);
         }
+        return;
     }
-    else {
-        gnrc_netapi_send(iface, pkt);
-    }
-}
-#else
-static inline void _send_to_iface(kernel_pid_t iface, gnrc_pktsnip_t *pkt)
-{
-    ((gnrc_netif_hdr_t *)pkt->data)->if_pid = iface;
-    gnrc_netapi_send(iface, pkt);
-}
 #endif
+    gnrc_netapi_send(iface, pkt);
+}
 
 /* functions for sending */
 static void _send_unicast(kernel_pid_t iface, uint8_t *dst_l2addr,

sys/net/gnrc/network_layer/ipv6/netif/gnrc_ipv6_netif.c

@@ -695,6 +695,7 @@ void gnrc_ipv6_netif_init_by_dev(void)
     for (size_t i = 0; i < ifnum; i++) {
         ipv6_addr_t addr;
         eui64_t iid;
+        uint16_t mtu;
         gnrc_ipv6_netif_t *ipv6_if = gnrc_ipv6_netif_get(ifs[i]);
 
         if (ipv6_if == NULL) {
@@ -730,6 +731,7 @@ void gnrc_ipv6_netif_init_by_dev(void)
         }
 #endif
 
+        /* set link-local address */
         if ((gnrc_netapi_get(ifs[i], NETOPT_IPV6_IID, 0, &iid,
                              sizeof(eui64_t)) < 0)) {
             mutex_unlock(&ipv6_if->mutex);
@@ -740,6 +742,16 @@ void gnrc_ipv6_netif_init_by_dev(void)
         ipv6_addr_set_link_local_prefix(&addr);
         _add_addr_to_entry(ipv6_if, &addr, 64, 0);
 
+        /* set link MTU */
+        if ((gnrc_netapi_get(ifs[i], NETOPT_MAX_PACKET_SIZE, 0, &mtu,
+                             sizeof(uint16_t)) >= 0)) {
+            if (mtu >= IPV6_MIN_MTU) {
+                ipv6_if->mtu = mtu;
+            }
+            /* otherwise leave at GNRC_IPV6_NETIF_DEFAULT_MTU as initialized in
+             * gnrc_ipv6_netif_add() */
+        }
+
         mutex_unlock(&ipv6_if->mutex);
     }
 }

sys/shell/commands/sc_netif.c

@@ -89,6 +89,11 @@ static void _set_usage(char *cmd_name)
          "       * \"state\" - set the device state\n");
 }
 
+static void _mtu_usage(char *cmd_name)
+{
+    printf("usage: %s <if_id> mtu <n>\n", cmd_name);
+}
+
 static void _flag_usage(char *cmd_name)
 {
     printf("usage: %s <if_id> [-]{promisc|autoack|preload|6lo|iphc}\n", cmd_name);
@@ -259,8 +264,11 @@ static void _netif_list(kernel_pid_t dev)
     }
 
 #ifdef MODULE_GNRC_IPV6_NETIF
-    if ((entry != NULL) && (entry->flags & GNRC_IPV6_NETIF_FLAGS_SIXLOWPAN)) {
+    if (entry != NULL) {
+        printf("MTU:%" PRIu16 "  ", entry->mtu);
+        if (entry->flags & GNRC_IPV6_NETIF_FLAGS_SIXLOWPAN) {
             printf("6LO  ");
+        }
         linebreak = true;
     }
 #endif
@@ -683,6 +691,33 @@ static int _netif_del(kernel_pid_t dev, char *addr_str)
 #endif
 }
 
+static int _netif_mtu(kernel_pid_t dev, char *mtu_str)
+{
+#ifdef MODULE_GNRC_IPV6_NETIF
+    int mtu;
+    gnrc_ipv6_netif_t *entry;
+    if (((mtu = atoi(mtu_str)) < IPV6_MIN_MTU) || (mtu > UINT16_MAX)) {
+        printf("error: MTU must be between %" PRIu16 " and %" PRIu16 "\n",
+               IPV6_MIN_MTU, UINT16_MAX);
+        return 1;
+    }
+    if ((entry = gnrc_ipv6_netif_get(dev)) == NULL) {
+        puts("error: unable to set MTU.");
+        return 1;
+    }
+    entry->mtu = IPV6_MIN_MTU;
+    printf("success: set MTU %" PRIu16 " interface %" PRIkernel_pid "\n", mtu,
+           dev);
+    return 0;
+#else
+    (void)dev;
+    (void)mtu_str;
+    puts("error: unable to set MTU.");
+    return 1;
+#endif
+}
+
+
 /* shell commands */
 int _netif_send(int argc, char **argv)
 {
@@ -777,6 +812,14 @@ int _netif_config(int argc, char **argv)
 
                 return _netif_del((kernel_pid_t)dev, argv[3]);
             }
+            else if (strcmp(argv[2], "mtu") == 0) {
+                if (argc < 4) {
+                    _mtu_usage(argv[0]);
+                    return 1;
+                }
+
+                return _netif_mtu((kernel_pid_t)dev, argv[3]);
+            }
             else {
                 return _netif_flag(argv[0], dev, argv[2]);
             }
@@ -789,6 +832,7 @@ int _netif_config(int argc, char **argv)
 
     printf("usage: %s [<if_id>]\n", argv[0]);
     _set_usage(argv[0]);
+    _mtu_usage(argv[0]);
     _flag_usage(argv[0]);
     _add_usage(argv[0]);
     _del_usage(argv[0]);