From 875c2d76943dd5ca2d14c13d2b787fe1edb104b6 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 26 Jan 2026 12:10:19 +0000
Subject: [PATCH] Fix BufferedSubStream double-dispose issue with ArrayPool

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>
---
 src/SharpCompress/IO/BufferedSubStream.cs     | 24 ++++++++++++-------
 .../Streams/SharpCompressStreamTest.cs        | 21 ++++++++++++++++
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/src/SharpCompress/IO/BufferedSubStream.cs b/src/SharpCompress/IO/BufferedSubStream.cs
index 2a5c917b..9ee22c05 100755
--- a/src/SharpCompress/IO/BufferedSubStream.cs
+++ b/src/SharpCompress/IO/BufferedSubStream.cs
@@ -29,17 +29,25 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
 #if DEBUG_STREAMS
         this.DebugDispose(typeof(BufferedSubStream));
 #endif
-        if (disposing)
+        if (_isDisposed)
+        {
+            return;
+        }
+        _isDisposed = true;
+
+        if (disposing && _cache is not null)
         {
             ArrayPool<byte>.Shared.Return(_cache);
+            _cache = null;
         }
         base.Dispose(disposing);
     }
 
     private int _cacheOffset;
     private int _cacheLength;
-    private readonly byte[] _cache = ArrayPool<byte>.Shared.Rent(81920);
+    private byte[]? _cache = ArrayPool<byte>.Shared.Rent(81920);
     private long origin;
+    private bool _isDisposed;
 
     private long BytesLeftToRead { get; set; }
 
@@ -61,7 +69,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
 
     private void RefillCache()
     {
-        var count = (int)Math.Min(BytesLeftToRead, _cache.Length);
+        var count = (int)Math.Min(BytesLeftToRead, _cache!.Length);
         _cacheOffset = 0;
         if (count == 0)
         {
@@ -83,7 +91,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
 
     private async ValueTask RefillCacheAsync(CancellationToken cancellationToken)
     {
-        var count = (int)Math.Min(BytesLeftToRead, _cache.Length);
+        var count = (int)Math.Min(BytesLeftToRead, _cache!.Length);
         _cacheOffset = 0;
         if (count == 0)
         {
@@ -118,7 +126,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
             }
 
             count = Math.Min(count, _cacheLength - _cacheOffset);
-            Buffer.BlockCopy(_cache, _cacheOffset, buffer, offset, count);
+            Buffer.BlockCopy(_cache!, _cacheOffset, buffer, offset, count);
             _cacheOffset += count;
         }
 
@@ -136,7 +144,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
             }
         }
 
-        return _cache[_cacheOffset++];
+        return _cache![_cacheOffset++];
     }
 
     public override async Task<int> ReadAsync(
@@ -159,7 +167,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
             }
 
             count = Math.Min(count, _cacheLength - _cacheOffset);
-            Buffer.BlockCopy(_cache, _cacheOffset, buffer, offset, count);
+            Buffer.BlockCopy(_cache!, _cacheOffset, buffer, offset, count);
             _cacheOffset += count;
         }
 
@@ -186,7 +194,7 @@ internal class BufferedSubStream : SharpCompressStream, IStreamStack
             }
 
             count = Math.Min(count, _cacheLength - _cacheOffset);
-            _cache.AsSpan(_cacheOffset, count).CopyTo(buffer.Span);
+            _cache!.AsSpan(_cacheOffset, count).CopyTo(buffer.Span);
             _cacheOffset += count;
         }
 
diff --git a/tests/SharpCompress.Test/Streams/SharpCompressStreamTest.cs b/tests/SharpCompress.Test/Streams/SharpCompressStreamTest.cs
index 44051226..f74a6670 100644
--- a/tests/SharpCompress.Test/Streams/SharpCompressStreamTest.cs
+++ b/tests/SharpCompress.Test/Streams/SharpCompressStreamTest.cs
@@ -97,4 +97,25 @@ public class SharpCompressStreamTests
             }
         }
     }
+
+    [Fact]
+    public void BufferedSubStream_DoubleDispose_DoesNotCorruptArrayPool()
+    {
+        // This test verifies that calling Dispose multiple times on BufferedSubStream
+        // doesn't return the same array to the pool twice, which would cause pool corruption
+        byte[] data = new byte[0x10000];
+        using (MemoryStream ms = new MemoryStream(data))
+        {
+            var stream = new BufferedSubStream(ms, 0, data.Length);
+
+            // First disposal
+            stream.Dispose();
+
+            // Second disposal should not throw or corrupt the pool
+            stream.Dispose();
+        }
+
+        // If we got here without an exception, the test passed
+        Assert.True(true);
+    }
 }