Validate decoder pipelines.

PDF decoders, AKA filters, can be chained together. There can be
an arbitrary number of decoding / decompressing filters in the pipeline,
but there should be at most 1 image decoder, and the image decoder
should only be at the end of the chain.

BUG=chromium:880675

Change-Id: Iffa27c70ec1ed7574e38e0de23413840ee900959
Reviewed-on: https://pdfium-review.googlesource.com/42711
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

1 files changed, 80 insertions, 0 deletions

diff --git a/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp b/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
index b6d7679ef5..a4572396e6 100644
--- a/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
+++ b/core/fpdfapi/parser/fpdf_parser_decode_unittest.cpp
@@ -4,9 +4,89 @@
 
 #include "core/fpdfapi/parser/fpdf_parser_decode.h"
 
+#include "core/fpdfapi/parser/cpdf_array.h"
+#include "core/fpdfapi/parser/cpdf_name.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
 
+TEST(fpdf_parser_decode, ValidateDecoderPipeline) {
+  {
+    // Empty decoder list is always valid.
+    CPDF_Array decoders;
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // 1 decoder is always valid.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("FlateEncode");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // 1 decoder is always valid, even with an unknown decoder.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("FooBar");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Valid 2 decoder pipeline.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("AHx");
+    decoders.AddNew<CPDF_Name>("LZWDecode");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Valid 2 decoder pipeline.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("ASCII85Decode");
+    decoders.AddNew<CPDF_Name>("ASCII85Decode");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Valid 5 decoder pipeline.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("ASCII85Decode");
+    decoders.AddNew<CPDF_Name>("A85");
+    decoders.AddNew<CPDF_Name>("RunLengthDecode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    decoders.AddNew<CPDF_Name>("RL");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Valid 5 decoder pipeline, with an image decoder at the end.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("RunLengthDecode");
+    decoders.AddNew<CPDF_Name>("ASCII85Decode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    decoders.AddNew<CPDF_Name>("LZW");
+    decoders.AddNew<CPDF_Name>("DCTDecode");
+    EXPECT_TRUE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Invalid 2 decoder pipeline, with 2 image decoders.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("DCTDecode");
+    decoders.AddNew<CPDF_Name>("CCITTFaxDecode");
+    EXPECT_FALSE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Invalid 2 decoder pipeline, with 1 image decoder at the start.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("DCTDecode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    EXPECT_FALSE(ValidateDecoderPipeline(&decoders));
+  }
+  {
+    // Invalid 5 decoder pipeline.
+    CPDF_Array decoders;
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    decoders.AddNew<CPDF_Name>("DCTDecode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    decoders.AddNew<CPDF_Name>("FlateDecode");
+    EXPECT_FALSE(ValidateDecoderPipeline(&decoders));
+  }
+}
+
 TEST(fpdf_parser_decode, A85Decode) {
   const pdfium::DecodeTestData test_data[] = {
       // Empty src string.