[release/7.0] Ensure free buffer space when reading TLS messages (#83574)

* Ensure free buffer space when reading TLS messages

* Move buffer expansion outside of the loop to prevent unbounded grow

* Fix failing tests

The initial size is not enough to cover later TLS frames

* Remove unwanted changes

---------

Co-authored-by: Radek Zikmund <[email protected]>
Co-authored-by: Radek Zikmund <[email protected]>
Co-authored-by: Radek Zikmund <[email protected]>

Author: github-actions[bot]

src/libraries/System.Net.Security/src/System/Net/Security/SslStream.IO.cs

@@ -686,8 +686,16 @@ private async ValueTask<int> EnsureFullTlsFrameAsync<TIOAdapter>(CancellationTok
 
             if (frameSize < int.MaxValue)
             {
+                // make sure we have space for the whole frame
                 _buffer.EnsureAvailableSpace(frameSize - _buffer.EncryptedLength);
             }
+            else
+            {
+                // move existing data to the beginning of the buffer (they will
+                // be couple of bytes only, otherwise we would have entire
+                // header and know exact size)
+                _buffer.EnsureAvailableSpace(_buffer.Capacity - _buffer.EncryptedLength);
+            }
 
             while (_buffer.EncryptedLength < frameSize)
             {