mDNS parser: skip a 'Record' on parse error

src/src/dns.cpp

@@ -142,6 +142,9 @@ bool parseRecord(const QByteArray &packet, quint16 &offset, Record &record)
     record.setType(type);
     record.setFlushCache(class_ & 0x8000);
     record.setTtl(ttl);
+
+    quint16 next_offset = offset + dataLen;
+
     switch (type) {
     case A:
     {
@@ -234,6 +237,7 @@ bool parseRecord(const QByteArray &packet, quint16 &offset, Record &record)
         offset += dataLen;
         break;
     }
+    offset = next_offset;
     return true;
 }
 
@@ -297,6 +301,9 @@ void writeRecord(QByteArray &packet, quint16 &offset, Record &record, QMap<QByte
 
 bool fromPacket(const QByteArray &packet, Message &message)
 {
+    static int reported_errors = 0;
+    const int MAX_REPORTED_ERRORS = 10;
+
     quint16 offset = 0;
     quint16 transactionId, flags, nQuestion, nAnswer, nAuthority, nAdditional;
     if (!parseInteger<quint16>(packet, offset, transactionId) ||
@@ -325,14 +332,29 @@ bool fromPacket(const QByteArray &packet, Message &message)
         message.addQuery(query);
     }
     quint16 nRecord = nAnswer + nAuthority + nAdditional;
+    bool with_error = false;
+    uint records = 0;
     for (int i = 0; i < nRecord; ++i) {
         Record record;
         if (!parseRecord(packet, offset, record)) {
-            return false;
+            with_error = true;
+        }
+        else {
+            message.addRecord(record);
+            records++;
         }
-        message.addRecord(record);
     }
-    return true;
+
+    if (with_error && reported_errors < MAX_REPORTED_ERRORS) {
+        qWarning() << "qmdnsengine: mDNS parse error, UDP payload is" << packet.toHex();
+        reported_errors++;
+        if (reported_errors == MAX_REPORTED_ERRORS) {
+            qWarning() << "qmdnsengine: no more similar errors be reported: maximum report count is reached.";
+        }
+    }
+
+    // this message will be processed further if at least one record was parsed
+    return records > 0;
 }
 
 void toPacket(const Message &message, QByteArray &packet)

tests/CMakeLists.txt

@@ -4,6 +4,7 @@ set(TESTS
     TestBrowser
     TestCache
     TestDns
+    TestFromPacket
     TestHostname
     TestProber
     TestProvider

tests/TestFromPacket.cpp

@@ -0,0 +1,58 @@
+#include <QTest>
+
+#include <qmdnsengine/dns.h>
+#include <qmdnsengine/record.h>
+#include <qmdnsengine/message.h>
+
+unsigned char b0[] = {
+    0x00, 0x00, 0x84, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x04,
+    0x10, 0x5f, 0x75, 0x6e, 0x69, 0x70, 0x72, 0x6f, 0x2d, 0x6c, 0x61, 0x70,
+    0x74, 0x69, 0x6d, 0x65, 0x72, 0x04, 0x5f, 0x74, 0x63, 0x70, 0x05, 0x6c,
+    0x6f, 0x63, 0x61, 0x6c, 0x00, 0x00, 0x0c, 0x00, 0x01, 0x00, 0x00, 0x11,
+    0x94, 0x00, 0x0e, 0x0b, 0x75, 0x6e, 0x69, 0x67, 0x6f, 0x2d, 0x31, 0x32,
+    0x33, 0x34, 0x35, 0xc0, 0x0c, 0xc0, 0x33, 0x00, 0x21, 0x80, 0x01, 0x00,
+    0x00, 0x00, 0x78, 0x00, 0x14, 0x00, 0x00, 0x00, 0x00, 0x1f, 0x90, 0x0b,
+    0x75, 0x6e, 0x69, 0x67, 0x6f, 0x2d, 0x31, 0x32, 0x33, 0x34, 0x35, 0xc0,
+    0x22, 0xc0, 0x53, 0x00, 0x2f, 0x80, 0x01, 0x00, 0x00, 0x11, 0x94, 0x00,
+    0x0a, 0xc0, 0x53, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x08, 0xc0,
+    0x53, 0x00, 0x01, 0x80, 0x01, 0x00, 0x00, 0x00, 0x78, 0x00, 0x04, 0xc0,
+    0xa8, 0x32, 0x45, 0xc0, 0x33, 0x00, 0x10, 0x80, 0x01, 0x00, 0x00, 0x11,
+    0x94, 0x00, 0x3d, 0x10, 0x4f, 0x77, 0x6e, 0x65, 0x72, 0x3d, 0x55, 0x6e,
+    0x69, 0x70, 0x72, 0x6f, 0x20, 0x41, 0x70, 0x73, 0x07, 0x44, 0x72, 0x69,
+    0x76, 0x65, 0x72, 0x3d, 0x0f, 0x4d, 0x6f, 0x64, 0x65, 0x6c, 0x3d, 0x55,
+    0x6e, 0x69, 0x47, 0x6f, 0x20, 0x4f, 0x6e, 0x65, 0x13, 0x73, 0x65, 0x72,
+    0x69, 0x61, 0x6c, 0x2d, 0x6e, 0x75, 0x6d, 0x62, 0x65, 0x72, 0x3d, 0x31,
+    0x32, 0x33, 0x34, 0x35
+};
+
+
+class TestFromPacket : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+
+    void testParseB0();
+};
+
+
+
+void TestFromPacket::testParseB0()
+{
+    /* This code mimics
+     * void ServerPrivate::onReadyRead()
+     *    ...
+     *    socket->readDatagram(packet.data(), packet.size(), &address, &port);
+     */
+
+    QByteArray packet = QByteArray::fromRawData(
+                (const char *)b0, sizeof(b0));
+
+    QMdnsEngine::Message message;
+
+    QVERIFY(fromPacket(packet, message));
+}
+
+
+QTEST_MAIN(TestFromPacket)
+#include "TestFromPacket.moc"