Merge pull request #2986 from brianberns/main

When decoding a compressed TIFF, truncate a too-long string instead of throwing an exception

Author: JimBobSquarePants

src/ImageSharp/Formats/Tiff/Compression/Decompressors/LzwString.cs

@@ -69,25 +69,33 @@ public int WriteTo(Span<byte> buffer, int offset)
             return 0;
         }
 
-        if (this.Length == 1)
+        int available = buffer.Length - offset;
+        if (available <= 0)
         {
-            buffer[offset] = this.value;
-            return 1;
+            return 0;
+        }
+
+        int numToWrite = this.Length;
+        if (numToWrite > available)
+        {
+            numToWrite = available;
         }
 
         LzwString e = this;
-        int endIdx = this.Length - 1;
-        if (endIdx >= buffer.Length)
+
+        // if string is too long, skip bytes at the end
+        int toSkip = this.Length - numToWrite;
+        for (int i = 0; i < toSkip; i++)
         {
-            TiffThrowHelper.ThrowImageFormatException("Error reading lzw compressed stream. Either pixel buffer to write to is to small or code length is invalid!");
+            e = e.previous;
         }
 
-        for (int i = endIdx; i >= 0; i--)
+        for (int i = numToWrite - 1; i >= 0; i--)
         {
             buffer[offset + i] = e.value;
             e = e.previous;
         }
 
-        return this.Length;
+        return numToWrite;
     }
 }

tests/ImageSharp.Tests/Formats/Tiff/TiffDecoderTests.cs

@@ -833,4 +833,9 @@ public void TiffDecoder_Decode_Resize<TPixel>(TestImageProvider<TPixel> provider
     [WithFile(ExtraSamplesUnspecified, PixelTypes.Rgba32)]
     public void TiffDecoder_CanDecode_ExtraSamplesUnspecified<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
+
+    [Theory]
+    [WithFile(Issue2983, PixelTypes.Rgba32)]
+    public void TiffDecoder_CanDecode_Issue2983<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -1164,6 +1164,7 @@ public static class Tiff
         public const string IptcData = "Tiff/iptc.tiff";
 
         public const string Issue2909 = "Tiff/Issues/Issue2909.tiff";
+        public const string Issue2983 = "Tiff/Issues/Issue2983.tiff";
 
         public static readonly string[] Multiframes = [MultiframeDeflateWithPreview, MultiframeLzwPredictor /*, MultiFrameDifferentSize, MultiframeDifferentSizeTiled, MultiFrameDifferentVariants,*/
         ];

tests/Images/Input/Tiff/Issues/Issue2983.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:7bfe1d8660d11111cdf2674aedc43c1362dc8c2ecfab9b74b43a06c7c195863e
+size 13311100