Merge pull request thomas-v2#47 from juwalter/master

S7p: Fix buffer length checks in decoding methods

Author: thomas-v2

src/S7CommPlusDriver/Core/S7p.cs

@@ -87,7 +87,7 @@ public static int EncodeInt64(System.IO.Stream buffer, Int64 value)
 
         public static int DecodeByte(System.IO.Stream buffer, out byte value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 1)
             {
                 value = 0;
                 return 0;
@@ -98,7 +98,7 @@ public static int DecodeByte(System.IO.Stream buffer, out byte value)
 
         public static int DecodeUInt16(System.IO.Stream buffer, out UInt16 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 2)
             {
                 value = 0;
                 return 0;
@@ -110,7 +110,7 @@ public static int DecodeUInt16(System.IO.Stream buffer, out UInt16 value)
         // Little Endian
         public static int DecodeUInt16LE(System.IO.Stream buffer, out UInt16 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 2)
             {
                 value = 0;
                 return 0;
@@ -121,7 +121,7 @@ public static int DecodeUInt16LE(System.IO.Stream buffer, out UInt16 value)
 
         public static int DecodeInt16(System.IO.Stream buffer, out Int16 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 2)
             {
                 value = 0;
                 return 0;
@@ -132,7 +132,7 @@ public static int DecodeInt16(System.IO.Stream buffer, out Int16 value)
 
         public static int DecodeUInt32(System.IO.Stream buffer, out UInt32 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 4)
             {
                 value = 0;
                 return 0;
@@ -144,7 +144,7 @@ public static int DecodeUInt32(System.IO.Stream buffer, out UInt32 value)
         // Little Endian
         public static int DecodeUInt32LE(System.IO.Stream buffer, out UInt32 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 4)
             {
                 value = 0;
                 return 0;
@@ -156,7 +156,7 @@ public static int DecodeUInt32LE(System.IO.Stream buffer, out UInt32 value)
         // Little Endian
         public static int DecodeInt32LE(System.IO.Stream buffer, out Int32 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 4)
             {
                 value = 0;
                 return 0;
@@ -167,7 +167,7 @@ public static int DecodeInt32LE(System.IO.Stream buffer, out Int32 value)
 
         public static int DecodeInt32(System.IO.Stream buffer, out Int32 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 4)
             {
                 value = 0;
                 return 0;
@@ -178,7 +178,7 @@ public static int DecodeInt32(System.IO.Stream buffer, out Int32 value)
 
         public static int DecodeUInt64(System.IO.Stream buffer, out UInt64 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 8)
             {
                 value = 0;
                 return 0;
@@ -192,7 +192,7 @@ public static int DecodeUInt64(System.IO.Stream buffer, out UInt64 value)
 
         public static int DecodeInt64(System.IO.Stream buffer, out Int64 value)
         {
-            if (buffer.Position >= buffer.Length)
+            if (buffer.Length - buffer.Position < 8)
             {
                 value = 0;
                 return 0;
@@ -600,6 +600,11 @@ public static int EncodeWString(System.IO.Stream buffer, string value)
 
         public static int DecodeWString(System.IO.Stream buffer, int length, out string value)
         {
+            if (buffer.Length - buffer.Position < length)
+            {
+                value = string.Empty;
+                return 0;
+            }
             byte[] tmp = new byte[length];
             buffer.Read(tmp, 0, length);
             value = Encoding.UTF8.GetString(tmp);
@@ -615,7 +620,7 @@ public static int EncodeOctets(System.IO.Stream buffer, byte[] value)
 
         public static int DecodeOctets(System.IO.Stream buffer, int length, out byte[] value)
         {
-            if (length <= 0)
+            if (length <= 0 || buffer.Length - buffer.Position < length)
             {
                 value = null;
                 return 0;
@@ -715,7 +720,14 @@ public static int DecodeObject(System.IO.Stream buffer, ref PObject obj, bool As
 
         public static int DecodeHeader(System.IO.Stream buffer, out byte version, out UInt16 length)
         {
-            buffer.ReadByte();
+            if (buffer.Length - buffer.Position < 4)
+            {
+                version = 0;
+                length = 0;
+                return 0;
+            }
+
+            buffer.ReadByte(); // Skip one byte (purpose unclear)
             version = (byte)buffer.ReadByte();
             DecodeUInt16(buffer, out length);
             return 4;