[net] Sanitize private keys recevied from SAM proxy

src/i2p.cpp

@@ -77,6 +77,19 @@ static Binary DecodeI2PBase64(const std::string& i2p_b64)
     return std::move(*decoded);
 }
 
+static Binary SanitizePrivKey(Binary&& binary)
+{
+    if (binary.size() < 387) {
+        throw std::runtime_error("Private key too small (size < 387 bytes)");
+    }
+
+    if (binary.size() > (387 + std::numeric_limits<uint16_t>::max())) {
+        throw std::runtime_error("Private key too large");
+    }
+
+    return binary;
+}
+
 /**
  * Derive the .b32.i2p address of an I2P destination (binary).
  * @param[in] dest I2P destination.
@@ -327,7 +340,7 @@ void Session::DestGenerate(const Sock& sock)
     // If SIGNATURE_TYPE is not specified, then the default one is DSA_SHA1.
     const Reply& reply = SendRequestAndGetReply(sock, "DEST GENERATE SIGNATURE_TYPE=7", false);
 
-    m_private_key = DecodeI2PBase64(reply.Get("PRIV"));
+    m_private_key = SanitizePrivKey(DecodeI2PBase64(reply.Get("PRIV")));
 }
 
 void Session::GenerateAndSavePrivateKey(const Sock& sock)
@@ -356,6 +369,10 @@ Binary Session::MyDestination() const
 
     const size_t dest_len = DEST_LEN_BASE + cert_len;
 
+    if (dest_len > m_private_key.size()) {
+        throw std::runtime_error("Certificate length did not match the actual private key length");
+    }
+
     return Binary{m_private_key.begin(), m_private_key.begin() + dest_len};
 }
 
@@ -382,13 +399,13 @@ void Session::CreateIfNotCreatedAlready()
                       "inbound.quantity=1 outbound.quantity=1",
                       session_id));
 
-        m_private_key = DecodeI2PBase64(reply.Get("DESTINATION"));
+        m_private_key = SanitizePrivKey(DecodeI2PBase64(reply.Get("DESTINATION")));
     } else {
         // Read our persistent destination (private key) from disk or generate
         // one and save it to disk. Then use it when creating the session.
         const auto& [read_ok, data] = ReadBinaryFile(m_private_key_file);
         if (read_ok) {
-            m_private_key.assign(data.begin(), data.end());
+            m_private_key = SanitizePrivKey(Binary{data.begin(), data.end()});
         } else {
             GenerateAndSavePrivateKey(*sock);
         }