Fix vold vulnerability in FrameworkListener

Modify FrameworkListener to ignore commands that exceed the maximum
buffer length and send an error message.

Bug: 29831647
Change-Id: I9e57d1648d55af2ca0191bb47868e375ecc26950
Signed-off-by: Connor O'Brien <connoro@google.com>
(cherry picked from commit baa126dc158a40bc83c17c6d428c760e5b93fb1a)

include/sysutils/FrameworkListener.h

@@ -32,6 +32,7 @@ private:
     int mCommandCount;
     bool mWithSeq;
     FrameworkCommandCollection *mCommands;
+    bool mSkipToNextNullByte;
 
 public:
     FrameworkListener(const char *socketName);

libsysutils/src/FrameworkListener.cpp

@@ -42,6 +42,7 @@ void FrameworkListener::init(const char *socketName, bool withSeq) {
     errorRate = 0;
     mCommandCount = 0;
     mWithSeq = withSeq;
+    mSkipToNextNullByte = false;
 }
 
 bool FrameworkListener::onDataAvailable(SocketClient *c) {
@@ -52,10 +53,15 @@ bool FrameworkListener::onDataAvailable(SocketClient *c) {
     if (len < 0) {
         SLOGE("read() failed (%s)", strerror(errno));
         return false;
-    } else if (!len)
+    } else if (!len) {
         return false;
-   if(buffer[len-1] != '\0')
+    } else if (buffer[len-1] != '\0') {
         SLOGW("String is not zero-terminated");
+        android_errorWriteLog(0x534e4554, "29831647");
+        c->sendMsg(500, "Command too large for buffer", false);
+        mSkipToNextNullByte = true;
+        return false;
+    }
 
     int offset = 0;
     int i;
@@ -63,11 +69,16 @@ bool FrameworkListener::onDataAvailable(SocketClient *c) {
     for (i = 0; i < len; i++) {
         if (buffer[i] == '\0') {
             /* IMPORTANT: dispatchCommand() expects a zero-terminated string */
-            dispatchCommand(c, buffer + offset);
+            if (mSkipToNextNullByte) {
+                mSkipToNextNullByte = false;
+            } else {
+                dispatchCommand(c, buffer + offset);
+            }
             offset = i + 1;
         }
     }
 
+    mSkipToNextNullByte = false;
     return true;
 }