Harden AEAD-4 bounds checks and add nonce wrap logging

- Fix potential unsigned overflow in createDatagram size check by
subtracting constants from MAX_PACKET_PAYLOAD instead of adding to
data_len
- Add upper-bound validation on src_len and assoc_len in aeadEncrypt and
aeadDecrypt
- Log peer name on AEAD nonce wraparound for debug builds

src/Mesh.cpp

@@ -531,7 +531,8 @@ Packet* Mesh::createDatagram(uint8_t type, const Identity& dest, const uint8_t*
   if (type == PAYLOAD_TYPE_TXT_MSG || type == PAYLOAD_TYPE_REQ || type == PAYLOAD_TYPE_RESPONSE) {
     size_t hash_prefix = PATH_HASH_SIZE * 2;  // dest_hash + src_hash
     size_t max_overhead = aead_nonce ? (AEAD_NONCE_SIZE + AEAD_TAG_SIZE) : (CIPHER_MAC_SIZE + CIPHER_BLOCK_SIZE-1);
-    if (data_len + hash_prefix + max_overhead > MAX_PACKET_PAYLOAD) return NULL;
+    size_t max_payload_data = MAX_PACKET_PAYLOAD - hash_prefix - max_overhead;
+    if (data_len > max_payload_data) return NULL;
   } else {
     return NULL;  // invalid type
   }

src/Utils.cpp

@@ -122,7 +122,8 @@ int Utils::aeadEncrypt(const uint8_t* shared_secret,
                        const uint8_t* assoc_data, int assoc_len,
                        uint16_t nonce_counter,
                        uint8_t dest_hash, uint8_t src_hash) {
-  if (src_len <= 0) return 0;
+  if (src_len <= 0 || src_len > MAX_PACKET_PAYLOAD) return 0;
+  if (assoc_len < 0 || assoc_len > MAX_PACKET_PAYLOAD) return 0;
 
   // Write nonce to output
   dest[0] = (uint8_t)(nonce_counter >> 8);
@@ -166,7 +167,8 @@ int Utils::aeadDecrypt(const uint8_t* shared_secret,
                        const uint8_t* assoc_data, int assoc_len,
                        uint8_t dest_hash, uint8_t src_hash) {
   // Minimum: nonce(2) + at least 1 byte ciphertext + tag(4)
-  if (src_len < AEAD_NONCE_SIZE + 1 + AEAD_TAG_SIZE) return 0;
+  if (src_len < AEAD_NONCE_SIZE + 1 + AEAD_TAG_SIZE || src_len > MAX_PACKET_PAYLOAD) return 0;
+  if (assoc_len < 0 || assoc_len > MAX_PACKET_PAYLOAD) return 0;
 
   int ct_len = src_len - AEAD_NONCE_SIZE - AEAD_TAG_SIZE;
 

src/helpers/ContactInfo.h

@@ -23,7 +23,10 @@ struct ContactInfo {
   // When 0, callers use ECB encryption.
   uint16_t nextAeadNonce() const {
     if (flags & CONTACT_FLAG_AEAD) {
-      if (++aead_nonce == 0) ++aead_nonce;  // skip 0 (sentinel for ECB)
+      if (++aead_nonce == 0) {
+        ++aead_nonce;  // skip 0 (sentinel for ECB)
+        MESH_DEBUG_PRINTLN("AEAD nonce wrapped for peer: %s", name);
+      }
       return aead_nonce;
     }
     return 0;