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Author: Rob-Hague

src/Renci.SshNet/Messages/Message.cs

@@ -1,6 +1,7 @@
 #nullable enable
 using System;
 using System.Diagnostics;
+using System.Globalization;
 using System.IO;
 
 using Renci.SshNet.Abstractions;
@@ -40,7 +41,10 @@ protected override void WriteBytes(SshDataStream stream)
             base.WriteBytes(stream);
         }
 
-        /// <returns>The number of bytes written to <paramref name="buffer"/>.</returns>
+        /// <returns>The number of bytes occupied by the packet in <paramref name="buffer"/>.</returns>
+        /// <remarks>
+        /// [4 bytes] || packet_len || padding_len || payload || padding || [macLength bytes].
+        /// </remarks>
         internal int GetPacket(ref byte[] buffer, byte paddingMultiplier, Compressor? compressor, bool excludePacketLengthFieldWhenPadding, int macLength)
         {
             const int outboundPacketSequenceSize = 4;
@@ -72,15 +76,20 @@ internal int GetPacket(ref byte[] buffer, byte paddingMultiplier, Compressor? co
             // in Encrypt-then-MAC mode or AEAD, the length field is not encrypted, so we should keep it out of the
             // padding length calculation
             var paddingLength = GetPaddingLength(
-                paddingMultiplier, excludePacketLengthFieldWhenPadding ? 1 + messageLength : 4 + 1 + messageLength);
+                paddingMultiplier, (excludePacketLengthFieldWhenPadding ? 0 : 4) + 1 + messageLength);
 
             var packetLength = 1 + messageLength + paddingLength;
 
             var bytesRequired = 4 + 4 + packetLength + macLength; // Includes space for sequence_num
 
+            if ((uint)bytesRequired > (uint)Session.MaximumSshPacketSize)
+            {
+                throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, "Packet is too big. Maximum packet size is {0} bytes.", Session.MaximumSshPacketSize));
+            }
+
             if (buffer.Length < bytesRequired)
             {
-                Array.Resize(ref buffer, Math.Max(bytesRequired, 2 * buffer.Length)); // TODO packetLength guard?
+                Array.Resize(ref buffer, Math.Max(bytesRequired, 2 * buffer.Length));
             }
 
             using (var sshDataStream = new SshDataStream(buffer))

src/Renci.SshNet/Session.cs

@@ -1085,11 +1085,6 @@ internal void SendMessage(Message message)
                     _clientEtm || _clientAead,
                     macLength);
 
-                if (activeBufferLength > MaximumSshPacketSize)
-                {
-                    throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, "Packet is too big. Maximum packet size is {0} bytes.", MaximumSshPacketSize));
-                }
-
                 // write outbound packet sequence to start of packet data
                 BinaryPrimitives.WriteUInt32BigEndian(_sendBuffer, _outboundPacketSequence);