Warn rather than segv on access after closing input source (fixes #495)

ChangeLog

@@ -1,3 +1,8 @@
+2021-01-06  Jay Berkenbilt  <ejb@ql.org>
+
+	* Give warnings instead of segfaulting if a QPDF operation is
+	attempted after calling closeInputSource(). Fixes #495.
+
 2021-01-05  Jay Berkenbilt  <ejb@ql.org>
 
 	* 10.1.0: release

libqpdf/QPDF.cc

@@ -45,6 +45,51 @@ static char const* EMPTY_PDF =
     "110\n"
     "%%EOF\n";
 
+class InvalidInputSource: public InputSource
+{
+  public:
+    virtual ~InvalidInputSource() = default;
+    virtual qpdf_offset_t findAndSkipNextEOL() override
+    {
+        throwException();
+        return 0;
+    }
+    virtual std::string const& getName() const override
+    {
+        static std::string name("closed input source");
+        return name;
+    }
+    virtual qpdf_offset_t tell() override
+    {
+        throwException();
+        return 0;
+    }
+    virtual void seek(qpdf_offset_t offset, int whence) override
+    {
+        throwException();
+    }
+    virtual void rewind() override
+    {
+        throwException();
+    }
+    virtual size_t read(char* buffer, size_t length) override
+    {
+        throwException();
+        return 0;
+    }
+    virtual void unreadCh(char ch) override
+    {
+        throwException();
+    }
+
+  private:
+    void throwException()
+    {
+        throw std::runtime_error(
+            "QPDF operation attempted after closing input source");
+    }
+};
+
 QPDF::ForeignStreamData::ForeignStreamData(
     PointerHolder<EncryptionParameters> encp,
     PointerHolder<InputSource> file,
@@ -254,7 +299,7 @@ QPDF::processInputSource(PointerHolder<InputSource> source,
 void
 QPDF::closeInputSource()
 {
-    this->m->file = 0;
+    this->m->file = new InvalidInputSource();
 }
 
 void

qpdf/qtest/qpdf.test

@@ -1215,7 +1215,13 @@ $td->runtest("check output",
 show_ntests();
 # ----------
 $td->notify("--- Invalid objects ---");
-$n_tests += 2;
+$n_tests += 3;
+
+$td->runtest("closed input source",
+	     {$td->COMMAND => "test_driver 73 minimal.pdf"},
+	     {$td->FILE => "test73.out",
+	      $td->EXIT_STATUS => 0},
+	     $td->NORMALIZE_NEWLINES);
 
 $td->runtest("empty object",
 	     {$td->COMMAND => "qpdf -show-object=7,0 empty-object.pdf"},

qpdf/qtest/qpdf/test73.out

@@ -0,0 +1,2 @@
+WARNING: closed input source: object 2/0: error reading object: QPDF operation attempted after closing input source
+test 73 done

qpdf/test_driver.cc

@@ -2300,6 +2300,11 @@ void runtest(int n, char const* filename1, char const* arg2)
             buf->getSize());
         assert(s.find("/bye") != std::string::npos);
     }
+    else if (n == 73)
+    {
+        pdf.closeInputSource();
+        pdf.getRoot().getKey("/Pages").unparseResolved();
+    }
     else
     {
 	throw std::runtime_error(std::string("invalid test ") +