Allow /P in encryption dictionary to be positive (fixes #382)

Even though this is disallowed by the spec, files like this have been
encountered in the wild.

8 files changed, 80 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index d2013565..3e3d7a4a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2019-11-09  Jay Berkenbilt  <ejb@ql.org>
+
+	* When reading /P from the encryption dictionary, use static_cast
+	instead of QIntC to convert the value to a signed integer. The
+	value of /P is a bit field, and PDF files have been found in the
+	wild where /P is represented as an unsigned integer even though
+	the spec states that it is a signed 32-bit value. By using
+	static_cast, we allow qpdf to compensate for writers that
+	incorrectly represent the correct bit field as an unsigned value.
+	Fixes #382.
+
 2019-11-05  Jay Berkenbilt  <ejb@ql.org>
 
 	* Add support for pluggable crypto providers, enabling multiple
diff --git a/libqpdf/QPDFPageObjectHelper.cc b/libqpdf/QPDFPageObjectHelper.cc
index 8ecd0144..d588c322 100644
--- a/libqpdf/QPDFPageObjectHelper.cc
+++ b/libqpdf/QPDFPageObjectHelper.cc
@@ -661,6 +661,7 @@ QPDFPageObjectHelper::getFormXObjectForPage(bool handle_transformations)
     return result;
 }
 
+// ABI: name should be std:string const&
 std::string
 QPDFPageObjectHelper::placeFormXObject(
     QPDFObjectHandle fo, std::string name,
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index a31f5da9..7b769ae4 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -762,7 +762,7 @@ QPDFWriter::copyEncryptionParameters(QPDF& qpdf)
 	    V,
 	    encrypt.getKey("/R").getIntValueAsInt(),
     	    key_len,
-	    encrypt.getKey("/P").getIntValueAsInt(),
+	    static_cast<int>(encrypt.getKey("/P").getIntValue()),
 	    encrypt.getKey("/O").getStringValue(),
 	    encrypt.getKey("/U").getStringValue(),
             OE,
diff --git a/libqpdf/QPDF_encryption.cc b/libqpdf/QPDF_encryption.cc
index 5a6735ee..9880face 100644
--- a/libqpdf/QPDF_encryption.cc
+++ b/libqpdf/QPDF_encryption.cc
@@ -877,7 +877,7 @@ QPDF::initializeEncryption()
     int R = encryption_dict.getKey("/R").getIntValueAsInt();
     std::string O = encryption_dict.getKey("/O").getStringValue();
     std::string U = encryption_dict.getKey("/U").getStringValue();
-    int P = encryption_dict.getKey("/P").getIntValueAsInt();
+    int P = static_cast<int>(encryption_dict.getKey("/P").getIntValue());
 
     // If supporting new encryption R/V values, remember to update
     // error message inside this if statement.
@@ -1448,7 +1448,7 @@ QPDF::isEncrypted(int& R, int& P, int& V,
 	QPDFObjectHandle Pkey = encrypt.getKey("/P");
 	QPDFObjectHandle Rkey = encrypt.getKey("/R");
         QPDFObjectHandle Vkey = encrypt.getKey("/V");
-	P = Pkey.getIntValueAsInt();
+	P = static_cast<int>(Pkey.getIntValue());
 	R = Rkey.getIntValueAsInt();
         V = Vkey.getIntValueAsInt();
         stream_method = this->m->encp->cf_stream;
diff --git a/qpdf/qtest/qpdf.test b/qpdf/qtest/qpdf.test
index 1df8291e..7ea329c2 100644
--- a/qpdf/qtest/qpdf.test
+++ b/qpdf/qtest/qpdf.test
@@ -721,6 +721,32 @@ foreach my $d (@bug_tests)
 }
 show_ntests();
 # ----------
+$td->notify("--- Positive /P in encryption dictionary ---");
+$n_tests += 4;
+
+# Files have been seen where /P in the encryption dictionary was an
+# unsigned rather than a signed integer. To create
+# encrypted-positive-P.pdf, I temporarily modified QPDFWriter.cc to
+# introduce this error.
+
+$td->runtest("decrypt positive P",
+	     {$td->COMMAND =>
+                  "qpdf --decrypt --static-id encrypted-positive-P.pdf a.pdf"},
+	     {$td->STRING => "", $td->EXIT_STATUS => 0});
+$td->runtest("check output",
+	     {$td->FILE => "a.pdf"},
+	     {$td->FILE => "decrypted-positive-P.pdf"});
+$td->runtest("copy encryption positive P",
+	     {$td->COMMAND =>
+                  "qpdf --static-id --static-aes-iv" .
+                  " encrypted-positive-P.pdf a.pdf"},
+	     {$td->STRING => "", $td->EXIT_STATUS => 0});
+$td->runtest("check output",
+	     {$td->FILE => "a.pdf"},
+	     {$td->FILE => "copied-positive-P.pdf"});
+
+show_ntests();
+# ----------
 $td->notify("--- Library version ---");
 $n_tests += 3;
 
diff --git a/qpdf/qtest/qpdf/copied-positive-P.pdf b/qpdf/qtest/qpdf/copied-positive-P.pdf
new file mode 100644
index 00000000..c13d9040
--- /dev/null
+++ b/qpdf/qtest/qpdf/copied-positive-P.pdf
diff --git a/qpdf/qtest/qpdf/decrypted-positive-P.pdf b/qpdf/qtest/qpdf/decrypted-positive-P.pdf
new file mode 100644
index 00000000..964a7c2c
--- /dev/null
+++ b/qpdf/qtest/qpdf/decrypted-positive-P.pdf
diff --git a/qpdf/qtest/qpdf/encrypted-positive-P.pdf b/qpdf/qtest/qpdf/encrypted-positive-P.pdf
new file mode 100644
index 00000000..e42772c4
--- /dev/null
+++ b/qpdf/qtest/qpdf/encrypted-positive-P.pdf
@@ -0,0 +1,39 @@
+%PDF-1.7
+%����
+1 0 obj
+<< /Extensions << /ADBE << /BaseVersion /1.7 /ExtensionLevel 8 >> >> /Pages 2 0 R /Type /Catalog >>
+endobj
+2 0 obj
+<< /Count 1 /Kids [ 3 0 R ] /Type /Pages >>
+endobj
+3 0 obj
+<< /Contents 4 0 R /MediaBox [ 0 0 612 792 ] /Parent 2 0 R /Resources << /Font << /F1 5 0 R >> /ProcSet 6 0 R >> /Type /Page >>
+endobj
+4 0 obj
+<< /Length 80 /Filter /FlateDecode >>
+stream
+P옃��Пu�@B�L$��:je^~[�j};C���5����\̉�.���(��do��F�
�G����*C5{��k�xQ�endstream
+endobj
+5 0 obj
+<< /BaseFont /Helvetica /Encoding /WinAnsiEncoding /Name /F1 /Subtype /Type1 /Type /Font >>
+endobj
+6 0 obj
+[ /PDF /Text ]
+endobj
+7 0 obj
+<< /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV3 /Length 32 >> >> /Filter /Standard /Length 256 /O <1b7cc50a8bd7d4220be2b990df3a3f82bf54a9596ea0d3f0fe308a62a496d7f2853cb41fd7e8f2adfee08f045f4579b0> /OE <968299e6df135ce14da318e851103f18c263082e6ae1380fcbf26e910cef551b> /P 4294967292 /Perms <afb6ec9c6b9c3e8c2fbdcb9c4f391a1d> /R 6 /StmF /StdCF /StrF /StdCF /U <16d19f98d4d5144f6e68ec10294e3789d8eab6a8eb6de68231d749c198904a004b8a16d4ceb3553204d16feae9d1b819> /UE <80044f0bc684a6675f129a0cb8a6ed6efa33d890a6195963a75e8b3876ded541> /V 5 >>
+endobj
+xref
+0 8
+0000000000 65535 f 
+0000000015 00000 n 
+0000000130 00000 n 
+0000000189 00000 n 
+0000000332 00000 n 
+0000000482 00000 n 
+0000000589 00000 n 
+0000000619 00000 n 
+trailer << /Root 1 0 R /Size 8 /ID [<7aed6705f40de848cd4f3ea12c672f33><7aed6705f40de848cd4f3ea12c672f33>] /Encrypt 7 0 R >>
+startxref
+1174
+%%EOF