Esempio n. 1
0
        /// <summary>Processes a TIFF IFD.</summary>
        /// <remarks>
        /// IFD Header:
        /// <list type="bullet">
        ///   <item><b>2 bytes</b> number of tags</item>
        /// </list>
        /// Tag structure:
        /// <list type="bullet">
        ///   <item><b>2 bytes</b> tag type</item>
        ///   <item><b>2 bytes</b> format code (values 1 to 12, inclusive)</item>
        ///   <item><b>4 bytes</b> component count</item>
        ///   <item><b>4 bytes</b> inline value, or offset pointer if too large to fit in four bytes</item>
        /// </list>
        /// </remarks>
        /// <param name="handler">the <see cref="ITiffHandler"/> that will coordinate processing and accept read values</param>
        /// <param name="reader">the <see cref="IndexedReader"/> from which the data should be read</param>
        /// <param name="processedGlobalIfdOffsets">the set of visited IFD offsets, to avoid revisiting the same IFD in an endless loop</param>
        /// <param name="ifdOffset">the offset within <c>reader</c> at which the IFD data starts</param>
        /// <exception cref="System.IO.IOException">an error occurred while accessing the required data</exception>
        public static void ProcessIfd(ITiffHandler handler, IndexedReader reader, ICollection <int> processedGlobalIfdOffsets, int ifdOffset)
        {
            try
            {
                // Check for directories we've already visited to avoid stack overflows when recursive/cyclic directory structures exist.
                // Note that we track these offsets in the global frame, not the reader's local frame.
                var globalIfdOffset = reader.ToUnshiftedOffset(ifdOffset);
                if (processedGlobalIfdOffsets.Contains(globalIfdOffset))
                {
                    return;
                }

                // Remember that we've visited this directory so that we don't visit it again later
                processedGlobalIfdOffsets.Add(globalIfdOffset);

                // Validate IFD offset
                if (ifdOffset >= reader.Length || ifdOffset < 0)
                {
                    handler.Error("Ignored IFD marked to start outside data segment");
                    return;
                }

                // First two bytes in the IFD are the number of tags in this directory
                int dirTagCount = reader.GetUInt16(ifdOffset);

                // Some software modifies the byte order of the file, but misses some IFDs (such as makernotes).
                // The entire test image repository doesn't contain a single IFD with more than 255 entries.
                // Here we detect switched bytes that suggest this problem, and temporarily swap the byte order.
                // This was discussed in GitHub issue #136.
                if (dirTagCount > 0xFF && (dirTagCount & 0xFF) == 0)
                {
                    dirTagCount >>= 8;
                    reader        = reader.WithByteOrder(!reader.IsMotorolaByteOrder);
                }

                var dirLength = 2 + 12 * dirTagCount + 4;
                if (dirLength + ifdOffset > reader.Length)
                {
                    handler.Error("Illegally sized IFD");
                    return;
                }

                //
                // Handle each tag in this directory
                //
                var invalidTiffFormatCodeCount = 0;
                for (var tagNumber = 0; tagNumber < dirTagCount; tagNumber++)
                {
                    var tagOffset = CalculateTagOffset(ifdOffset, tagNumber);

                    // 2 bytes for the tag id
                    int tagId = reader.GetUInt16(tagOffset);

                    // 2 bytes for the format code
                    var formatCode = (TiffDataFormatCode)reader.GetUInt16(tagOffset + 2);

                    // 4 bytes dictate the number of components in this tag's data
                    var componentCount = reader.GetUInt32(tagOffset + 4);

                    var format = TiffDataFormat.FromTiffFormatCode(formatCode);

                    long byteCount;
                    if (format == null)
                    {
                        if (!handler.TryCustomProcessFormat(tagId, formatCode, componentCount, out byteCount))
                        {
                            // This error suggests that we are processing at an incorrect index and will generate
                            // rubbish until we go out of bounds (which may be a while).  Exit now.
                            handler.Error($"Invalid TIFF tag format code {formatCode} for tag 0x{tagId:X4}");
                            // TODO specify threshold as a parameter, or provide some other external control over this behaviour
                            if (++invalidTiffFormatCodeCount > 5)
                            {
                                handler.Error("Stopping processing as too many errors seen in TIFF IFD");
                                return;
                            }
                            continue;
                        }
                    }
                    else
                    {
                        byteCount = componentCount * format.ComponentSizeBytes;
                    }

                    long tagValueOffset;
                    if (byteCount > 4)
                    {
                        // If it's bigger than 4 bytes, the dir entry contains an offset.
                        tagValueOffset = reader.GetUInt32(tagOffset + 8);
                        if (tagValueOffset + byteCount > reader.Length)
                        {
                            // Bogus pointer offset and / or byteCount value
                            handler.Error("Illegal TIFF tag pointer offset");
                            continue;
                        }
                    }
                    else
                    {
                        // 4 bytes or less and value is in the dir entry itself.
                        tagValueOffset = tagOffset + 8;
                    }

                    if (tagValueOffset < 0 || tagValueOffset > reader.Length)
                    {
                        handler.Error("Illegal TIFF tag pointer offset");
                        continue;
                    }

                    // Check that this tag isn't going to allocate outside the bounds of the data array.
                    // This addresses an uncommon OutOfMemoryError.
                    if (byteCount < 0 || tagValueOffset + byteCount > reader.Length)
                    {
                        handler.Error("Illegal number of bytes for TIFF tag data: " + byteCount);
                        continue;
                    }

                    // Some tags point to one or more additional IFDs to process
                    var isIfdPointer = false;
                    if (byteCount == checked (4L * componentCount))
                    {
                        for (var i = 0; i < componentCount; i++)
                        {
                            if (handler.TryEnterSubIfd(tagId))
                            {
                                isIfdPointer = true;
                                var subDirOffset = reader.GetUInt32((int)(tagValueOffset + i * 4));
                                ProcessIfd(handler, reader, processedGlobalIfdOffsets, (int)subDirOffset);
                            }
                        }
                    }

                    // If it wasn't an IFD pointer, allow custom tag processing to occur
                    if (!isIfdPointer && !handler.CustomProcessTag((int)tagValueOffset, processedGlobalIfdOffsets, reader, tagId, (int)byteCount))
                    {
                        // If no custom processing occurred, process the tag in the standard fashion
                        ProcessTag(handler, tagId, (int)tagValueOffset, (int)componentCount, formatCode, reader);
                    }
                }

                // at the end of each IFD is an optional link to the next IFD
                var finalTagOffset = CalculateTagOffset(ifdOffset, dirTagCount);
                var nextIfdOffset  = reader.GetInt32(finalTagOffset);
                if (nextIfdOffset != 0)
                {
                    if (nextIfdOffset >= reader.Length)
                    {
                        // Last 4 bytes of IFD reference another IFD with an address that is out of bounds
                        return;
                    }
                    else if (nextIfdOffset < ifdOffset)
                    {
                        // TODO is this a valid restriction?
                        // Last 4 bytes of IFD reference another IFD with an address that is before the start of this directory
                        return;
                    }

                    if (handler.HasFollowerIfd())
                    {
                        ProcessIfd(handler, reader, processedGlobalIfdOffsets, nextIfdOffset);
                    }
                }
            }
            finally
            {
                handler.EndingIfd();
            }
        }
Esempio n. 2
0
        /// <summary>Processes a TIFF IFD.</summary>
        /// <remarks>
        /// IFD Header:
        /// <list type="bullet">
        ///   <item><b>2 bytes</b> number of tags</item>
        /// </list>
        /// Tag structure:
        /// <list type="bullet">
        ///   <item><b>2 bytes</b> tag type</item>
        ///   <item><b>2 bytes</b> format code (values 1 to 12, inclusive)</item>
        ///   <item><b>4 bytes</b> component count</item>
        ///   <item><b>4 bytes</b> inline value, or offset pointer if too large to fit in four bytes</item>
        /// </list>
        /// </remarks>
        /// <param name="handler">the <see cref="ITiffHandler"/> that will coordinate processing and accept read values</param>
        /// <param name="reader">the <see cref="IndexedReader"/> from which the data should be read</param>
        /// <param name="processedIfdOffsets">the set of visited IFD offsets, to avoid revisiting the same IFD in an endless loop</param>
        /// <param name="ifdOffset">the offset within <c>reader</c> at which the IFD data starts</param>
        /// <param name="tiffHeaderOffset">the offset within <c>reader</c> at which the TIFF header starts</param>
        /// <exception cref="System.IO.IOException">an error occurred while accessing the required data</exception>
        public static void ProcessIfd([NotNull] ITiffHandler handler, [NotNull] IndexedReader reader, [NotNull] ICollection <int> processedIfdOffsets, int ifdOffset, int tiffHeaderOffset)
        {
            try
            {
                // check for directories we've already visited to avoid stack overflows when recursive/cyclic directory structures exist
                if (processedIfdOffsets.Contains(ifdOffset))
                {
                    return;
                }

                // remember that we've visited this directory so that we don't visit it again later
                processedIfdOffsets.Add(ifdOffset);
                if (ifdOffset >= reader.Length || ifdOffset < 0)
                {
                    handler.Error("Ignored IFD marked to start outside data segment");
                    return;
                }

                // First two bytes in the IFD are the number of tags in this directory
                int dirTagCount = reader.GetUInt16(ifdOffset);
                var dirLength   = (2 + (12 * dirTagCount) + 4);
                if (dirLength + ifdOffset > reader.Length)
                {
                    handler.Error("Illegally sized IFD");
                    return;
                }

                //
                // Handle each tag in this directory
                //
                var invalidTiffFormatCodeCount = 0;
                for (var tagNumber = 0; tagNumber < dirTagCount; tagNumber++)
                {
                    var tagOffset = CalculateTagOffset(ifdOffset, tagNumber);

                    // 2 bytes for the tag id
                    int tagId = reader.GetUInt16(tagOffset);

                    // 2 bytes for the format code
                    var formatCode = (TiffDataFormatCode)reader.GetUInt16(tagOffset + 2);
                    var format     = TiffDataFormat.FromTiffFormatCode(formatCode);
                    if (format == null)
                    {
                        // This error suggests that we are processing at an incorrect index and will generate
                        // rubbish until we go out of bounds (which may be a while).  Exit now.
                        handler.Error("Invalid TIFF tag format code: " + formatCode);
                        // TODO specify threshold as a parameter, or provide some other external control over this behaviour
                        if (++invalidTiffFormatCodeCount > 5)
                        {
                            handler.Error("Stopping processing as too many errors seen in TIFF IFD");
                            return;
                        }
                        continue;
                    }

                    // 4 bytes dictate the number of components in this tag's data
                    var componentCount = reader.GetInt32(tagOffset + 4);
                    if (componentCount < 0)
                    {
                        handler.Error("Negative TIFF tag component count");
                        continue;
                    }

                    var byteCount = componentCount * format.ComponentSizeBytes;
                    int tagValueOffset;
                    if (byteCount > 4)
                    {
                        // If it's bigger than 4 bytes, the dir entry contains an offset.
                        var offsetVal = reader.GetInt32(tagOffset + 8);
                        if (offsetVal + byteCount > reader.Length)
                        {
                            // Bogus pointer offset and / or byteCount value
                            handler.Error("Illegal TIFF tag pointer offset");
                            continue;
                        }
                        tagValueOffset = tiffHeaderOffset + offsetVal;
                    }
                    else
                    {
                        // 4 bytes or less and value is in the dir entry itself.
                        tagValueOffset = tagOffset + 8;
                    }

                    if (tagValueOffset < 0 || tagValueOffset > reader.Length)
                    {
                        handler.Error("Illegal TIFF tag pointer offset");
                        continue;
                    }

                    // Check that this tag isn't going to allocate outside the bounds of the data array.
                    // This addresses an uncommon OutOfMemoryError.
                    if (byteCount < 0 || tagValueOffset + byteCount > reader.Length)
                    {
                        handler.Error("Illegal number of bytes for TIFF tag data: " + byteCount);
                        continue;
                    }

                    //
                    // Special handling for tags that point to other IFDs
                    //
                    if (byteCount == 4 && handler.IsTagIfdPointer(tagId))
                    {
                        var subDirOffset = tiffHeaderOffset + reader.GetInt32(tagValueOffset);
                        ProcessIfd(handler, reader, processedIfdOffsets, subDirOffset, tiffHeaderOffset);
                    }
                    else if (!handler.CustomProcessTag(tagValueOffset, processedIfdOffsets, tiffHeaderOffset, reader, tagId, byteCount))
                    {
                        ProcessTag(handler, tagId, tagValueOffset, componentCount, formatCode, reader);
                    }
                }

                // at the end of each IFD is an optional link to the next IFD
                var finalTagOffset = CalculateTagOffset(ifdOffset, dirTagCount);
                var nextIfdOffset  = reader.GetInt32(finalTagOffset);
                if (nextIfdOffset != 0)
                {
                    nextIfdOffset += tiffHeaderOffset;

                    if (nextIfdOffset >= reader.Length)
                    {
                        // Last 4 bytes of IFD reference another IFD with an address that is out of bounds
                        // Note this could have been caused by jhead 1.3 cropping too much
                        return;
                    }
                    else if (nextIfdOffset < ifdOffset)
                    {
                        // TODO is this a valid restriction?
                        // Last 4 bytes of IFD reference another IFD with an address that is before the start of this directory
                        return;
                    }

                    if (handler.HasFollowerIfd())
                    {
                        ProcessIfd(handler, reader, processedIfdOffsets, nextIfdOffset, tiffHeaderOffset);
                    }
                }
            }
            finally
            {
                handler.EndingIfd();
            }
        }