Validate collection sizes before allocating (#1848)

Validate cases where (in particular) a few bytes of server data determines the size of
a collection allocated, and throw if it's not possible based on the size of the buffer
that the collection is purported to be contained in.

src/Renci.SshNet/Common/SshDataStream.cs

@@ -371,12 +371,9 @@ namespace Renci.SshNet.Common
         /// <exception cref="ArgumentOutOfRangeException"><paramref name="length"/> is greater than the internal buffer size.</exception>
         internal byte[] ReadBytes(int length)
         {
-            var data = new byte[length];
-            var bytesRead = Read(data, 0, length);
-            if (bytesRead < length)
-            {
-                throw new ArgumentOutOfRangeException(nameof(length), string.Format(CultureInfo.InvariantCulture, "The requested length ({0}) is greater than the actual number of bytes read ({1}).", length, bytesRead));
-            }
+            var data = GetRemainingBuffer().Slice(0, length).ToArray();
+
+            Position += length;
 
             return data;
         }

src/Renci.SshNet/Sftp/Responses/SftpNameResponse.cs

@@ -1,7 +1,10 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Text;
 
+using Renci.SshNet.Common;
+
 namespace Renci.SshNet.Sftp.Responses
 {
     internal sealed class SftpNameResponse : SftpResponse
@@ -29,6 +32,13 @@ namespace Renci.SshNet.Sftp.Responses
             base.LoadData();
 
             Count = ReadUInt32();
+
+            // Each entry is at least two uints in size.
+            if (Count > (DataStream.Length - DataStream.Position) / 8)
+            {
+                throw new SshException(string.Format(CultureInfo.InvariantCulture, "Invalid SSH_FXP_NAME count: {0}.", Count));
+            }
+
             Files = new KeyValuePair<string, SftpFileAttributes>[Count];
 
             for (var i = 0; i < Count; i++)

src/Renci.SshNet/Sftp/SftpFileAttributes.cs

@@ -3,6 +3,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
 using System.Linq;
 using System.Text;
 
@@ -820,8 +821,15 @@ namespace Renci.SshNet.Sftp
 
             if ((flag & SSH_FILEXFER_ATTR_EXTENDED) == SSH_FILEXFER_ATTR_EXTENDED)
             {
-                var extendedCount = (int)stream.ReadUInt32();
-                extensions = new Dictionary<string, string>(extendedCount);
+                var extendedCount = stream.ReadUInt32();
+
+                // Each extension is at least two string lengths.
+                if (extendedCount > (stream.Length - stream.Position) / 8)
+                {
+                    throw new SshException(string.Format(CultureInfo.InvariantCulture, "Invalid extended attribute count: {0}.", extendedCount));
+                }
+
+                extensions = new Dictionary<string, string>((int)extendedCount);
                 for (var i = 0; i < extendedCount; i++)
                 {
                     var extensionName = stream.ReadString(Encoding.UTF8);

test/Renci.SshNet.Tests/Classes/Common/SshDataTest.cs

@@ -102,23 +102,15 @@ namespace Renci.SshNet.Tests.Classes.Common
         }
 
         [TestMethod]
-        public void ReadBytes_Length_LengthIsGreaterThanNumberOfBytesAvailable()
+        [DataRow(4)]
+        [DataRow(int.MaxValue)]
+        public void ReadBytes_Length_LengthIsGreaterThanNumberOfBytesAvailable(int length)
         {
             MySshData sshData = new MySshData();
 
             sshData.Load(new byte[] { 0x01, 0x0d, 0x0a }, 0, 3);
 
-            try
-            {
-                sshData.ReadBytes(4);
-                Assert.Fail();
-            }
-            catch (ArgumentOutOfRangeException ex)
-            {
-                Assert.AreEqual(typeof(ArgumentOutOfRangeException), ex.GetType());
-                Assert.IsNull(ex.InnerException);
-                Assert.AreEqual("length", ex.ParamName);
-            }
+            Assert.Throws<ArgumentException>(() => sshData.ReadBytes(length));
         }
 
         [TestMethod]

test/Renci.SshNet.Tests/Classes/Sftp/Responses/SftpNameResponseTest.cs

@@ -0,0 +1,47 @@
+using System.Text;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using Renci.SshNet.Common;
+using Renci.SshNet.Sftp.Responses;
+
+namespace Renci.SshNet.Tests.Classes.Sftp.Responses
+{
+    [TestClass]
+    public class SftpNameResponseTest
+    {
+        [TestMethod]
+        public void Load()
+        {
+            var target = new SftpNameResponse(3, Encoding.UTF8);
+
+            target.Load([
+                0, 0, 0, 7, // response id
+                0, 0, 0, 1, // count
+                0, 0, 0, 1, (byte)'a', // filename
+                0, 0, 0, 0, // longname
+                0, 0, 0, 0, // attribute flags
+            ]);
+
+            Assert.AreEqual(7u, target.ResponseId);
+            Assert.HasCount(1, target.Files);
+            Assert.AreEqual("a", target.Files[0].Key);
+        }
+
+        [TestMethod]
+        public void Load_CountExceedsData_Throws()
+        {
+            var target = new SftpNameResponse(3, Encoding.UTF8);
+
+            var ex = Assert.ThrowsExactly<SshException>(() => target.Load([
+                0, 0, 0, 7, // response id
+                0xFF, 0xFF, 0xFF, 0xFF, // count
+                0, 0, 0, 1, (byte)'a', // filename
+                0, 0, 0, 0, // longname
+                0, 0, 0, 0, // attribute flags
+            ]));
+
+            Assert.AreEqual("Invalid SSH_FXP_NAME count: 4294967295.", ex.Message);
+        }
+    }
+}

test/Renci.SshNet.Tests/Classes/Sftp/SftpFileAttributesTest.cs

@@ -44,6 +44,19 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             Assert.AreEqual(isNamedPipe, attributes.IsNamedPipe);
         }
 
+        [TestMethod]
+        public void FromBytes_ExtendedCountExceedsData_Throws()
+        {
+            var ex = Assert.ThrowsExactly<SshException>(() => SftpFileAttributes.FromBytes([
+                0x80, 0, 0, 0, // flags: extended
+                0x7F, 0xFF, 0xFF, 0xFF, // extended count
+                0, 0, 0, 1, (byte)'a', // extension name
+                0, 0, 0, 1, (byte)'b', // extension data
+            ]));
+
+            Assert.AreEqual("Invalid extended attribute count: 2147483647.", ex.Message);
+        }
+
         [TestMethod]
         public void FromBytesGetBytes()
         {