Support (and add more documentation on) a variety of uncommon BMP cases.

* "Bitmap Array" files (OS/2)
* BITMAPV2HEADER info headers (Photoshop?)
* BITMAPV3HEADER info headers (Photoshop?)
* BI_ALPHABITFIELDS compression (Windows CE)
* 2bpp palettes (Windows CE)
* Top-down bitmaps with RLE compression (illegal per spec, but supported by
  Windows and Firefox)
* Truncated color palettes

This increases the number of testcases Chrome can render on
http://entropymine.com/jason/bmpsuite/bmpsuite/html/bmpsuite.html .

Bug: 552274
Change-Id: I4c86b8328d326992a2ebca2e5178727aeab3afc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769524
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@chromium.org>
Reviewed-by: Leon Scroggins <scroggo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690377}

third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_decoder.cc

@@ -98,21 +98,17 @@ bool BMPImageDecoder::DecodeHelper(bool only_size) {
 bool BMPImageDecoder::ProcessFileHeader(size_t& img_data_offset) {
   // Read file header.
   DCHECK(!decoded_offset_);
-  if (data_->size() < kSizeOfFileHeader)
-    return false;
-
-  char buffer[kSizeOfFileHeader];
   FastSharedBufferReader fast_reader(data_);
-  const char* file_header =
-      fast_reader.GetConsecutiveData(0, kSizeOfFileHeader, buffer);
-  const uint16_t file_type =
-      (file_header[0] << 8) | static_cast<uint8_t>(file_header[1]);
-  img_data_offset = BMPImageReader::ReadUint32(&file_header[10]);
-  decoded_offset_ = kSizeOfFileHeader;
+  char buffer[kSizeOfFileHeader];
+  const char* file_header;
+  uint16_t file_type;
+  if (!GetFileType(fast_reader, buffer, file_header, file_type))
+    return false;
 
   // See if this is a bitmap filetype we understand.
   enum {
-    BMAP = 0x424D,  // "BM"
+    BMAP = 0x424D,         // "BM"
+    BITMAPARRAY = 0x4241,  // "BA"
     // The following additional OS/2 2.x header values (see
     // http://www.fileformat.info/format/os2bmp/egff.htm ) aren't widely
     // decoded, and are unlikely to be in much use.
@@ -121,10 +117,32 @@ bool BMPImageDecoder::ProcessFileHeader(size_t& img_data_offset) {
     POINTER = 0x5054,  // "PT"
     COLORICON = 0x4349,  // "CI"
     COLORPOINTER = 0x4350,  // "CP"
-    BITMAPARRAY = 0x4241,  // "BA"
     */
   };
-  return (file_type == BMAP) || SetFailed();
+  if (file_type == BITMAPARRAY) {
+    // Skip initial 14-byte header, try to read the first entry as a BMAP.
+    decoded_offset_ += kSizeOfFileHeader;
+    if (!GetFileType(fast_reader, buffer, file_header, file_type))
+      return false;
+  }
+  if (file_type != BMAP)
+    return SetFailed();
+
+  img_data_offset = BMPImageReader::ReadUint32(&file_header[10]);
+  decoded_offset_ += kSizeOfFileHeader;
+  return true;
+}
+
+bool BMPImageDecoder::GetFileType(const FastSharedBufferReader& fast_reader,
+                                  char* buffer,
+                                  const char*& file_header,
+                                  uint16_t& file_type) const {
+  if (data_->size() - decoded_offset_ < kSizeOfFileHeader)
+    return false;
+  file_header = fast_reader.GetConsecutiveData(decoded_offset_,
+                                               kSizeOfFileHeader, buffer);
+  file_type = (file_header[0] << 8) | static_cast<uint8_t>(file_header[1]);
+  return true;
 }
 
 }  // namespace blink

third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_decoder.h

@@ -37,6 +37,7 @@
 namespace blink {
 
 class BMPImageReader;
+class FastSharedBufferReader;
 
 // This class decodes the BMP image format.
 class PLATFORM_EXPORT BMPImageDecoder final : public ImageDecoder {
@@ -72,6 +73,14 @@ class PLATFORM_EXPORT BMPImageDecoder final : public ImageDecoder {
   // file header could be decoded.
   bool ProcessFileHeader(size_t& img_data_offset);
 
+  // Uses |fast_reader| and |buffer| to read the file header into |file_header|.
+  // Computes |file_type| from the file header.  Returns whether there was
+  // sufficient data available to read the header.
+  bool GetFileType(const FastSharedBufferReader& fast_reader,
+                   char* buffer,
+                   const char*& file_header,
+                   uint16_t& file_type) const;
+
   // An index into |data_| representing how much we've already decoded.
   // Note that this only tracks data _this_ class decodes; once the
   // BMPImageReader takes over this will not be updated further.

third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.h

@@ -96,6 +96,7 @@ class PLATFORM_EXPORT BMPImageReader final {
     BITFIELDS = 3,
     JPEG = 4,
     PNG = 5,
+    ALPHABITFIELDS = 6,  // Windows CE only
     // OS/2 2.x-only
     HUFFMAN1D,  // Stored in file as 3
     RLE24,      // Stored in file as 4
@@ -154,16 +155,29 @@ class PLATFORM_EXPORT BMPImageReader final {
   // of header values from the byte stream.  Returns false on error.
   bool ReadInfoHeader();
 
-  // Returns true if this is a Windows V4+ BMP.
-  inline bool IsWindowsV4Plus() const {
-    // Windows V4 info header is 108 bytes.  V5 is 124 bytes.
-    return (info_header_.bi_size == 108) || (info_header_.bi_size == 124);
+  // Returns true if this BMP has an alpha mask in the info header
+  // (BITMAPV3HEADER+).  See comments in ReadInfoHeader() for more.
+  inline bool HasAlphaMaskInHeader() const {
+    // BITMAPV3HEADER is 56 bytes; this is also a valid OS/2 2.x header size, so
+    // exclude that case.
+    return (info_header_.bi_size == 56 && !is_os22x_) ||  // BITMAPV3HEADER
+           (info_header_.bi_size == 108) ||               // BITMAPV4HEADER
+           (info_header_.bi_size == 124);                 // BITMAPV5HEADER
+  }
+
+  // Returns true if this BMP has RGB masks in the info header
+  // (BITMAPV2HEADER+).  See comments in ReadInfoHeader() for more.
+  inline bool HasRGBMasksInHeader() const {
+    // BITMAPV2HEADER is 52 bytes; this is also a valid OS/2 2.x header size, so
+    // exclude that case.
+    return (info_header_.bi_size == 52 && !is_os22x_) ||  // BITMAPV2HEADER
+           HasAlphaMaskInHeader();                        // BITMAPV3HEADER+
   }
 
   // Returns false if consistency errors are found in the info header.
   bool IsInfoHeaderValid() const;
 
-  // For BI_BITFIELDS images, initializes the bit_masks_[] and
+  // For BI_[ALPHA]BITFIELDS images, initializes the bit_masks_[] and
   // bit_offsets_[] arrays.  ProcessInfoHeader() will initialize these for
   // other compression types where needed.
   bool ProcessBitmasks();

third_party/blink/renderer/platform/image-decoders/image_decoder.cc

@@ -62,7 +62,7 @@ inline bool MatchesCURSignature(const char* contents) {
 }
 
 inline bool MatchesBMPSignature(const char* contents) {
-  return !memcmp(contents, "BM", 2);
+  return !memcmp(contents, "BM", 2) || !memcmp(contents, "BA", 2);
 }
 
 static constexpr size_t kLongestSignatureLength = sizeof("RIFF????WEBPVP") - 1;