Support translating ICMP errors.

When receiving ICMPv6 messages from IPv6-only nodes, use
255.0.0.<ttl> as a fake IPv4 source address. It's better than
nothing.

Bug: 8276725
Change-Id: Iae93f75764cb9cd875af9bb5f1862a0dce2c2fa7

1 files changed, 181 insertions, 0 deletions

diff --git a/icmp.c b/icmp.c
new file mode 100644
index 0000000..af96b83
--- /dev/null
+++ b/icmp.c
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * icmp.c - convenience functions for translating ICMP and ICMPv6 packets.
+ */
+
+#include <netinet/in.h>
+#include <netinet/ip_icmp.h>
+#include <netinet/icmp6.h>
+#include <linux/icmp.h>
+
+#include "logging.h"
+#include "icmp.h"
+
+/* function: icmp_guess_ttl
+ * Guesses the number of hops a received packet has traversed based on its TTL.
+ * ttl - the ttl of the received packet.
+ */
+uint8_t icmp_guess_ttl(uint8_t ttl) {
+  if (ttl > 128) {
+    return 255 - ttl;
+  } else if (ttl > 64) {
+    return 128 - ttl;
+  } else if (ttl > 32) {
+    return 64 - ttl;
+  } else {
+    return 32 - ttl;
+  }
+}
+
+/* function: is_icmp_error
+ * Determines whether an ICMP type is an error message.
+ * type: the ICMP type
+ */
+int is_icmp_error(uint8_t type) {
+  return type == 3 || type == 11 || type == 12;
+}
+
+/* function: is_icmp6_error
+ * Determines whether an ICMPv6 type is an error message.
+ * type: the ICMPv6 type
+ */
+int is_icmp6_error(uint8_t type) {
+  return type < 128;
+}
+
+/* function: icmp_to_icmp6_type
+ * Maps ICMP types to ICMPv6 types. Partial implementation of RFC 6145, section 4.2.
+ * type - the ICMPv6 type
+ */
+uint8_t icmp_to_icmp6_type(uint8_t type, uint8_t code) {
+  switch (type) {
+    case ICMP_ECHO:
+      return ICMP6_ECHO_REQUEST;
+
+    case ICMP_ECHOREPLY:
+      return ICMP6_ECHO_REPLY;
+
+    case ICMP_TIME_EXCEEDED:
+      return ICMP6_TIME_EXCEEDED;
+
+    case ICMP_DEST_UNREACH:
+      // These two types need special translation which we don't support yet.
+      if (code != ICMP_UNREACH_PROTOCOL && code != ICMP_UNREACH_NEEDFRAG) {
+        return ICMP6_DST_UNREACH;
+      }
+  }
+
+  // We don't understand this ICMP type. Return parameter problem so the caller will bail out.
+  logmsg_dbg(ANDROID_LOG_DEBUG, "icmp_to_icmp6_type: unhandled ICMP type %d", type);
+  return ICMP6_PARAM_PROB;
+}
+
+/* function: icmp_to_icmp6_code
+ * Maps ICMP codes to ICMPv6 codes. Partial implementation of RFC 6145, section 4.2.
+ * type - the ICMP type
+ * code - the ICMP code
+ */
+uint8_t icmp_to_icmp6_code(uint8_t type, uint8_t code) {
+  switch (type) {
+    case ICMP_ECHO:
+    case ICMP_ECHOREPLY:
+      return 0;
+
+    case ICMP_TIME_EXCEEDED:
+      return code;
+
+    case ICMP_DEST_UNREACH:
+      switch (code) {
+        case ICMP_UNREACH_NET:
+        case ICMP_UNREACH_HOST:
+          return ICMP6_DST_UNREACH_NOROUTE;
+
+        case ICMP_UNREACH_PORT:
+          return ICMP6_DST_UNREACH_NOPORT;
+
+        case ICMP_UNREACH_NET_PROHIB:
+        case ICMP_UNREACH_HOST_PROHIB:
+        case ICMP_UNREACH_FILTER_PROHIB:
+        case ICMP_UNREACH_PRECEDENCE_CUTOFF:
+          return ICMP6_DST_UNREACH_ADMIN;
+
+        // Otherwise, we don't understand this ICMP type/code combination. Fall through.
+      }
+  }
+  logmsg_dbg(ANDROID_LOG_DEBUG, "icmp_to_icmp6_code: unhandled ICMP type/code %d/%d", type, code);
+  return 0;
+}
+
+/* function: icmp6_to_icmp_type
+ * Maps ICMPv6 types to ICMP types. Partial implementation of RFC 6145, section 5.2.
+ * type - the ICMP type
+ */
+uint8_t icmp6_to_icmp_type(uint8_t type, uint8_t code) {
+  switch (type) {
+    case ICMP6_ECHO_REQUEST:
+      return ICMP_ECHO;
+
+    case ICMP6_ECHO_REPLY:
+      return ICMP_ECHOREPLY;
+
+    case ICMP6_DST_UNREACH:
+      return ICMP_DEST_UNREACH;
+
+    case ICMP6_TIME_EXCEEDED:
+      return ICMP_TIME_EXCEEDED;
+  }
+
+  // We don't understand this ICMP type. Return parameter problem so the caller will bail out.
+  logmsg_dbg(ANDROID_LOG_DEBUG, "icmp6_to_icmp_type: unhandled ICMP type %d", type);
+  return ICMP_PARAMETERPROB;
+}
+
+/* function: icmp6_to_icmp_code
+ * Maps ICMPv6 codes to ICMP codes. Partial implementation of RFC 6145, section 5.2.
+ * type - the ICMPv6 type
+ * code - the ICMPv6 code
+ */
+uint8_t icmp6_to_icmp_code(uint8_t type, uint8_t code) {
+  switch (type) {
+    case ICMP6_ECHO_REQUEST:
+    case ICMP6_ECHO_REPLY:
+    case ICMP6_TIME_EXCEEDED:
+      return code;
+
+    case ICMP6_DST_UNREACH:
+      switch (code) {
+        case ICMP6_DST_UNREACH_NOROUTE:
+          return ICMP_UNREACH_HOST;
+
+        case ICMP6_DST_UNREACH_ADMIN:
+          return ICMP_UNREACH_HOST_PROHIB;
+
+        case ICMP6_DST_UNREACH_BEYONDSCOPE:
+          return ICMP_UNREACH_HOST;
+
+        case ICMP6_DST_UNREACH_ADDR:
+          return ICMP_HOST_UNREACH;
+
+        case ICMP6_DST_UNREACH_NOPORT:
+          return ICMP_UNREACH_PORT;
+
+        // Otherwise, we don't understand this ICMPv6 type/code combination. Fall through.
+      }
+  }
+
+  logmsg_dbg(ANDROID_LOG_DEBUG, "icmp6_to_icmp_code: unhandled ICMP type/code %d/%d", type, code);
+  return 0;
+}