Merge pull request #2077 in SNORT/snort3 from ~DERAMADA/snort3:gre_encode to master

Squashed commit of the following:

commit 14d1ebcee5a9b038c75e7c7ef2b5889dbe1e512f
Author: deramada <deramada@cisco.com>
Date:   Thu Mar 12 16:50:17 2020 -0400

    codecs: Update GRE flags and offset for injected packets

commit 2c99419277fa13e61819e54db9848c5fa523bf34
Author: Katura Harvey <katharve@cisco.com>
Date:   Thu Feb 20 13:24:39 2020 -0500

    codecs: GRE checksum updated for injected and rewritten packets

diff --git a/src/codecs/ip/cd_gre.cc b/src/codecs/ip/cd_gre.cc
index 8f4abc8577bdc263b0e840d89cc5122f4f8ea38d..d25e3a02cde1359cbf0ad22aeaaf16d258748831 100644 (file)
--- a/src/codecs/ip/cd_gre.cc
+++ b/src/codecs/ip/cd_gre.cc
@@ -29,6 +29,8 @@
 #include "main/snort_config.h"
 #include "protocols/gre.h"
 
+#include "checksum.h"
+
 #ifdef UNIT_TEST
 #include "catch/snort_catch.h"
 #endif
@@ -70,6 +72,8 @@ public:
     void log(TextLog* const, const uint8_t* pkt, const uint16_t len) override;
     bool encode(const uint8_t* const raw_in, const uint16_t raw_len,
         EncState&, Buffer&, Flow*) override;
+    void update(const ip::IpApi& api, const EncodeFlags flags, uint8_t* raw_pkt,
+        uint16_t lyr_len, uint32_t& updated_len) override;
 };
 
 static const uint32_t GRE_HEADER_LEN = 4;
@@ -101,16 +105,26 @@ void GreCodec::get_protocol_ids(std::vector<ProtocolId>& v)
  * see RFCs 1701, 2784 and 2637
  */
 
-bool GreCodec::encode(const uint8_t* const raw_in, const uint16_t raw_len,
-    EncState& enc, Buffer& buf, Flow*)
-
+void GreCodec::update(const ip::IpApi& api, const EncodeFlags /*flags*/, uint8_t* raw_pkt,
+    uint16_t lyr_len, uint32_t& updated_len)
 {
-    if (raw_len > GRE_HEADER_LEN)
+    UNUSED(api);
+    gre::GREHdr* const greh = reinterpret_cast<gre::GREHdr*>(raw_pkt);
+
+    updated_len += lyr_len;
+
+    if (GRE_CHKSUM(greh))
     {
-        ErrorMessage("Invalid GRE header length: %u",raw_len);
-        return false;
+        assert(lyr_len >= 6);
+        // Checksum field is zero for computing checksum
+        *(uint16_t*)(raw_pkt + 4) = 0;
+        *(uint16_t*)(raw_pkt + 4) = checksum::cksum_add((uint16_t*)raw_pkt, updated_len);
     }
+}
 
+bool GreCodec::encode(const uint8_t* const raw_in, const uint16_t raw_len,
+    EncState& enc, Buffer& buf, Flow*)
+{
     if (!buf.allocate(raw_len))
         return false;
 
@@ -119,7 +133,27 @@ bool GreCodec::encode(const uint8_t* const raw_in, const uint16_t raw_len,
     enc.next_proto = IpProtocol::GRE;
     enc.next_ethertype = greh_out->proto();
 
-    GRE_CHKSUM(greh_out);
+    if (GRE_SEQ(greh_out))
+    {
+        uint16_t len = 4; // Flags, version and protocol
+        
+        if (GRE_CHKSUM(greh_out))
+            len += 4;
+
+        if (GRE_KEY(greh_out))
+            len += 4;
+
+        *(uint32_t*)(buf.data() + len) += ntohl(1);
+    }
+
+    if (GRE_CHKSUM(greh_out))
+    {
+        assert(raw_len >= 6);
+        // Checksum field is zero for computing checksum
+        *(uint16_t*)(buf.data() + 4) = 0;
+        *(uint16_t*)(buf.data() + 4) = checksum::cksum_add((uint16_t*)buf.data(), 
+            buf.size());
+    }
 
     return true;
 }