Detect recoverable but invalid zlib data streams (fixes #562)

ChangeLog

@@ -1,5 +1,18 @@
 2021-11-02  Jay Berkenbilt  <ejb@ql.org>
 
+	* zlib-flate: warn and exit with code 3 when there is corrupted
+	input data even when decompression is possible. We do this in the
+	zlib-flate CLI so that it can be more reliably used to test the
+	validity of zlib streams, but we don't warn by default in qpdf
+	itself because PDF files in the wild exist with this problem and
+	other readers appear to tolerate it. There is a PDF in the qpdf
+	test suite (form-filled-by-acrobat.pdf) that was written by a
+	version of Adobe Acrobat that exhibits this problem. Fixes #562.
+
+	* Add Pl_Flate::setWarnCallback to make it possible to be notified
+	of data errors that are recoverable but still indicate invalid
+	data.
+
 	* Improve error reporting when someone forgets the -- after
 	--pages. Fixes #555.
 

include/qpdf/Pl_Flate.hh

@@ -23,6 +23,7 @@
 #define PL_FLATE_HH
 
 #include <qpdf/Pipeline.hh>
+#include <functional>
 
 class Pl_Flate: public Pipeline
 {
@@ -52,9 +53,13 @@ class Pl_Flate: public Pipeline
     QPDF_DLL
     static void setCompressionLevel(int);
 
+    QPDF_DLL
+    void setWarnCallback(std::function<void(char const*, int)> callback);
+
   private:
     void handleData(unsigned char* data, size_t len, int flush);
     void checkError(char const* prefix, int error_code);
+    void warn(char const*, int error_code);
 
     class Members
     {
@@ -73,6 +78,7 @@ class Pl_Flate: public Pipeline
         action_e action;
         bool initialized;
         void* zdata;
+        std::function<void(char const*, int)> callback;
     };
 
     PointerHolder<Members> m;

libqpdf/Pl_Flate.cc

@@ -71,6 +71,21 @@ Pl_Flate::~Pl_Flate()
 {
 }
 
+void
+Pl_Flate::setWarnCallback(std::function<void(char const*, int)> callback)
+{
+    this->m->callback = callback;
+}
+
+void
+Pl_Flate::warn(char const* msg, int code)
+{
+    if (this->m->callback != nullptr)
+    {
+        this->m->callback(msg, code);
+    }
+}
+
 void
 Pl_Flate::write(unsigned char* data, size_t len)
 {
@@ -164,7 +179,14 @@ Pl_Flate::handleData(unsigned char* data, size_t len, int flush)
 	    // Probably shouldn't be able to happen, but possible as a
 	    // boundary condition: if the last call to inflate exactly
 	    // filled the output buffer, it's possible that the next
-	    // call to inflate could have nothing to do.
+	    // call to inflate could have nothing to do. There are PDF
+	    // files in the wild that have this error (including at
+	    // least one in qpdf's test suite). In some cases, we want
+	    // to know about this, because it indicates incorrect
+	    // compression, so call a callback if provided.
+            this->warn(
+                "input stream is complete but output may still be valid",
+                err);
 	    done = true;
 	    break;
 
@@ -231,8 +253,15 @@ Pl_Flate::finish()
     }
     catch (std::exception& e)
     {
-        this->getNext()->finish();
+        try
-        throw e;
+        {
+            this->getNext()->finish();
+        }
+        catch (...)
+        {
+            // ignore secondary exception
+        }
+        throw std::runtime_error(e.what());
     }
     this->getNext()->finish();
 }

libqpdf/QPDF_Stream.cc

@@ -503,6 +503,14 @@ QPDF_Stream::pipeStreamData(Pipeline* pipeline, bool* filterp,
             {
                 pipeline = decode_pipeline;
             }
+            Pl_Flate* flate = dynamic_cast<Pl_Flate*>(pipeline);
+            if (flate != nullptr)
+            {
+                flate->setWarnCallback([this](char const* msg, int code) {
+                    warn(QPDFExc(qpdf_e_damaged_pdf, qpdf->getFilename(),
+                                 "", this->offset, msg));
+                });
+            }
 	}
     }
 

qpdf/qtest/qpdf/form-filled-by-acrobat-warn.out

@@ -0,0 +1,4 @@
+WARNING: form-filled-by-acrobat.pdf (offset 56091): input stream is complete but output may still be valid
+WARNING: form-filled-by-acrobat.pdf (offset 56420): input stream is complete but output may still be valid
+WARNING: form-filled-by-acrobat.pdf (offset 56657): input stream is complete but output may still be valid
+qpdf: operation succeeded with warnings; resulting file may have some problems

zlib-flate/qtest/missing-z-finish.in

@@ -0,0 +1,2 @@
+xÚ»Ô⻈Q<EFBFBD>Å£úÙÑr#UÆ?—0&¹±I%ê¬Õd‘JIY¶Ò’‘y!ã’ä²Ô¢TC=c=ƒä¼ÄÜ%Iiyé¾®‘AžŽ>Éiy%0vRz^–—«£Ÿ‚<C5B8>¨gprz^	˜ká¦ä'eZšëXèY&–4®L*IÏ´0105¶400K*)Éò	0247´´Ð5NÊMLu
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zlib-flate/qtest/zf.test

@@ -29,4 +29,11 @@ $td->runtest("error",
 	      $td->EXIT_STATUS => 2},
 	     $td->NORMALIZE_NEWLINES);
 
-$td->report(7);
+$td->runtest("corrupted input",
+	     {$td->COMMAND => "zlib-flate -uncompress < missing-z-finish.in"},
+	     {$td->REGEXP =>
+                  "input stream is complete but output may still be valid",
+                  $td->EXIT_STATUS => 3},
+	     $td->NORMALIZE_NEWLINES);
+
+$td->report(8);

zlib-flate/zlib-flate.cc

@@ -76,6 +76,12 @@ int main(int argc, char* argv[])
     PointerHolder<Pl_StdioFile> out = new Pl_StdioFile("stdout", stdout);
     PointerHolder<Pl_Flate> flate =
         new Pl_Flate("flate", out.getPointer(), action);
+    bool warn = false;
+    flate->setWarnCallback([&warn](char const* msg, int code) {
+        warn = true;
+        std::cerr << whoami << ": WARNING: zlib code " << code
+                  << ", msg = " << msg << std::endl;
+    });
 
     try
     {
@@ -97,9 +103,13 @@ int main(int argc, char* argv[])
     }
     catch (std::exception& e)
     {
-	std::cerr << e.what() << std::endl;
+	std::cerr << whoami << ": " << e.what() << std::endl;
 	exit(2);
     }
 
+    if (warn)
+    {
+        exit(3);
+    }
     return 0;
 }