lib/barrier: Disconnect client on too long input packets

This commit is the 3/3 part of the fix for the following security
vulnerability:
 - CVE-2021-42076 DoS via excess length messages

The issue has been reported by Matthias Gerstner <mgerstner@suse.de>.

src/lib/barrier/PacketStreamFilter.cpp

@@ -17,6 +17,7 @@
  */
 
 #include "barrier/PacketStreamFilter.h"
+#include "barrier/protocol_types.h"
 #include "base/IEventQueue.h"
 #include "mt/Lock.h"
 #include "base/TMethodEventJob.h"
@@ -133,8 +134,7 @@ PacketStreamFilter::isReadyNoLock() const
     return (m_size != 0 && m_buffer.getSize() >= m_size);
 }
 
-void
-PacketStreamFilter::readPacketSize()
+bool PacketStreamFilter::readPacketSize()
 {
     // note -- m_mutex must be locked on entry
 
@@ -146,7 +146,13 @@ PacketStreamFilter::readPacketSize()
                  ((UInt32)buffer[1] << 16) |
                  ((UInt32)buffer[2] <<  8) |
                   (UInt32)buffer[3];
+
+        if (m_size > PROTOCOL_MAX_MESSAGE_LENGTH) {
+            m_events->addEvent(Event(m_events->forIStream().inputFormatError(), getEventTarget()));
+            return false;
+        }
     }
+    return true;
 }
 
 bool
@@ -160,13 +166,17 @@ PacketStreamFilter::readMore()
     UInt32 n = getStream()->read(buffer, sizeof(buffer));
     while (n > 0) {
         m_buffer.write(buffer, n);
+
+        // if we don't yet have the next packet size then get it, if possible.
+        // Note that we can't wait for whole pending data to arrive because it may be huge in
+        // case of malicious or erroneous peer.
+        if (!readPacketSize()) {
+            break;
+        }
+
         n = getStream()->read(buffer, sizeof(buffer));
     }
 
-    // if we don't yet have the next packet size then get it,
-    // if possible.
-    readPacketSize();
-
     // note if we now have a whole packet
     bool isReady = isReadyNoLock();
 

src/lib/barrier/PacketStreamFilter.h

@@ -47,7 +47,9 @@ protected:
 
 private:
     bool                isReadyNoLock() const;
-    void                readPacketSize();
+
+    // returns false on erroneous packet size
+    bool readPacketSize();
     bool                readMore();
 
 private:

src/lib/barrier/protocol_types.h

@@ -20,6 +20,8 @@
 
 #include "base/EventTypes.h"
 
+#include <cstdint>
+
 // protocol version number
 // 1.0:  initial protocol
 // 1.1:  adds KeyCode to key press, release, and repeat
@@ -53,6 +55,7 @@ static const double        kHeartBeatsUntilDeath = 3.0;
 
 // Messages of very large size indicate a likely protocol error. We don't parse such messages and
 // drop connection instead. Note that e.g. the clipboard messages are already limited to 32kB.
+static constexpr std::uint32_t PROTOCOL_MAX_MESSAGE_LENGTH = 4 * 1024 * 1024;
 static constexpr std::uint32_t PROTOCOL_MAX_LIST_LENGTH = 1024 * 1024;
 static constexpr std::uint32_t PROTOCOL_MAX_STRING_LENGTH = 1024 * 1024;
 

src/lib/base/EventTypes.cpp

@@ -56,6 +56,7 @@ REGISTER_EVENT(IStream, outputFlushed)
 REGISTER_EVENT(IStream, outputError)
 REGISTER_EVENT(IStream, inputShutdown)
 REGISTER_EVENT(IStream, outputShutdown)
+REGISTER_EVENT(IStream, inputFormatError)
 
 //
 // IpcClient

src/lib/base/EventTypes.h

@@ -133,6 +133,11 @@ public:
     */
     Event::Type        outputShutdown();
 
+    /** Get input format error event type
+
+        This is sent when a stream receives an irrecoverable input format error.
+    */
+    Event::Type inputFormatError();
     //@}
 
 private:
@@ -141,6 +146,7 @@ private:
     Event::Type        m_outputError;
     Event::Type        m_inputShutdown;
     Event::Type        m_outputShutdown;
+    Event::Type m_inputFormatError;
 };
 
 class IpcClientEvents : public EventTypes {

src/lib/server/ClientProxy1_0.cpp

@@ -51,6 +51,10 @@ ClientProxy1_0::ClientProxy1_0(const std::string& name, barrier::IStream* stream
                             stream->getEventTarget(),
                             new TMethodEventJob<ClientProxy1_0>(this,
                                 &ClientProxy1_0::handleDisconnect, NULL));
+    m_events->adoptHandler(m_events->forIStream().inputFormatError(),
+                           stream->getEventTarget(),
+                           new TMethodEventJob<ClientProxy1_0>(this,
+                                &ClientProxy1_0::handleDisconnect, NULL));
     m_events->adoptHandler(m_events->forIStream().outputShutdown(),
                             stream->getEventTarget(),
                             new TMethodEventJob<ClientProxy1_0>(this,
@@ -90,6 +94,8 @@ ClientProxy1_0::removeHandlers()
                             getStream()->getEventTarget());
     m_events->removeHandler(m_events->forIStream().outputShutdown(),
                             getStream()->getEventTarget());
+    m_events->removeHandler(m_events->forIStream().inputFormatError(),
+                            getStream()->getEventTarget());
     m_events->removeHandler(Event::kTimer, this);
 
     // remove timer

src/lib/server/ClientProxyUnknown.cpp

@@ -118,6 +118,10 @@ ClientProxyUnknown::addStreamHandlers()
                             m_stream->getEventTarget(),
                             new TMethodEventJob<ClientProxyUnknown>(this,
                                 &ClientProxyUnknown::handleDisconnect));
+    m_events->adoptHandler(m_events->forIStream().inputFormatError(),
+                           m_stream->getEventTarget(),
+                           new TMethodEventJob<ClientProxyUnknown>(this,
+                                &ClientProxyUnknown::handleDisconnect));
     m_events->adoptHandler(m_events->forIStream().outputShutdown(),
                             m_stream->getEventTarget(),
                             new TMethodEventJob<ClientProxyUnknown>(this,
@@ -149,6 +153,8 @@ ClientProxyUnknown::removeHandlers()
                             m_stream->getEventTarget());
         m_events->removeHandler(m_events->forIStream().inputShutdown(),
                             m_stream->getEventTarget());
+        m_events->removeHandler(m_events->forIStream().inputFormatError(),
+                                m_stream->getEventTarget());
         m_events->removeHandler(m_events->forIStream().outputShutdown(),
                             m_stream->getEventTarget());
     }