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Added sentinel to ClientAuthentication.TryAuthenticate() to prevent stack overflow. #2

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Added sentinel to ClientAuthentication.TryAuthenticate() to prevent stack overflow. #2

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28 changes: 28 additions & 0 deletions Renci.SshNet.sln
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Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2013
VisualStudioVersion = 12.0.40629.0
MinimumVisualStudioVersion = 10.0.40219.1
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Renci.SshNet", "Renci.SshNet\Renci.SshNet.csproj", "{2F5F8C90-0BD1-424F-997C-7BC6280919D1}"
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestConsole", "TestConsole\TestConsole\TestConsole.csproj", "{96BCEC43-5B29-4E29-82F8-CC4A2DDC97BD}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
Release|Any CPU = Release|Any CPU
EndGlobalSection
GlobalSection(ProjectConfigurationPlatforms) = postSolution
{2F5F8C90-0BD1-424F-997C-7BC6280919D1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{2F5F8C90-0BD1-424F-997C-7BC6280919D1}.Debug|Any CPU.Build.0 = Debug|Any CPU
{2F5F8C90-0BD1-424F-997C-7BC6280919D1}.Release|Any CPU.ActiveCfg = Release|Any CPU
{2F5F8C90-0BD1-424F-997C-7BC6280919D1}.Release|Any CPU.Build.0 = Release|Any CPU
{96BCEC43-5B29-4E29-82F8-CC4A2DDC97BD}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{96BCEC43-5B29-4E29-82F8-CC4A2DDC97BD}.Debug|Any CPU.Build.0 = Debug|Any CPU
{96BCEC43-5B29-4E29-82F8-CC4A2DDC97BD}.Release|Any CPU.ActiveCfg = Release|Any CPU
{96BCEC43-5B29-4E29-82F8-CC4A2DDC97BD}.Release|Any CPU.Build.0 = Release|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
EndGlobal
336 changes: 175 additions & 161 deletions Renci.SshNet/ClientAuthentication.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,165 +5,179 @@

namespace Renci.SshNet
{
internal class ClientAuthentication
{
public void Authenticate(IConnectionInfoInternal connectionInfo, ISession session)
{
if (connectionInfo == null)
throw new ArgumentNullException("connectionInfo");
if (session == null)
throw new ArgumentNullException("session");

session.RegisterMessage("SSH_MSG_USERAUTH_FAILURE");
session.RegisterMessage("SSH_MSG_USERAUTH_SUCCESS");
session.RegisterMessage("SSH_MSG_USERAUTH_BANNER");
session.UserAuthenticationBannerReceived += connectionInfo.UserAuthenticationBannerReceived;

try
{
// the exception to report an authentication failure with
SshAuthenticationException authenticationException = null;

// try to authenticate against none
var noneAuthenticationMethod = connectionInfo.CreateNoneAuthenticationMethod();

var authenticated = noneAuthenticationMethod.Authenticate(session);
if (authenticated != AuthenticationResult.Success)
{
if (!TryAuthenticate(session, new AuthenticationState(connectionInfo.AuthenticationMethods.ToList()), noneAuthenticationMethod.AllowedAuthentications.ToList(), ref authenticationException))
{
throw authenticationException;
}
}
}
finally
{
session.UserAuthenticationBannerReceived -= connectionInfo.UserAuthenticationBannerReceived;
session.UnRegisterMessage("SSH_MSG_USERAUTH_FAILURE");
session.UnRegisterMessage("SSH_MSG_USERAUTH_SUCCESS");
session.UnRegisterMessage("SSH_MSG_USERAUTH_BANNER");
}

}

private bool TryAuthenticate(ISession session,
AuthenticationState authenticationState,
ICollection<string> allowedAuthenticationMethods,
ref SshAuthenticationException authenticationException)
{
if (!allowedAuthenticationMethods.Any())
{
authenticationException = new SshAuthenticationException("No authentication methods defined on SSH server.");
return false;
}

// we want to try authentication methods in the order in which they were
// passed in the ctor, not the order in which the SSH server returns
// the allowed authentication methods
var matchingAuthenticationMethods = authenticationState.SupportedAuthenticationMethods.Where(a => allowedAuthenticationMethods.Contains(a.Name)).ToList();
if (!matchingAuthenticationMethods.Any())
{
authenticationException = new SshAuthenticationException(string.Format("No suitable authentication method found to complete authentication ({0}).", string.Join(",", allowedAuthenticationMethods.ToArray())));
return false;
}

foreach (var authenticationMethod in GetOrderedAuthenticationMethods(authenticationState, matchingAuthenticationMethods))
{
if (authenticationState.FailedAuthenticationMethods.Contains(authenticationMethod))
continue;

// when the authentication method was previously executed, then skip the authentication
// method as long as there's another authentication method to try; this is done to avoid
// a stack overflow for servers that do not update the list of allowed authentication
// methods after a partial success

if (!authenticationState.ExecutedAuthenticationMethods.Contains(authenticationMethod))
{
// update state to reflect previosuly executed authentication methods
authenticationState.ExecutedAuthenticationMethods.Add(authenticationMethod);
}

var authenticationResult = authenticationMethod.Authenticate(session);
switch (authenticationResult)
{
case AuthenticationResult.PartialSuccess:
if (TryAuthenticate(session, authenticationState, authenticationMethod.AllowedAuthentications.ToList(), ref authenticationException))
{
authenticationResult = AuthenticationResult.Success;
}
break;
case AuthenticationResult.Failure:
authenticationState.FailedAuthenticationMethods.Add(authenticationMethod);
authenticationException = new SshAuthenticationException(string.Format("Permission denied ({0}).", authenticationMethod.Name));
break;
case AuthenticationResult.Success:
authenticationException = null;
break;
}

if (authenticationResult == AuthenticationResult.Success)
return true;
}

return false;
}

private IEnumerable<IAuthenticationMethod> GetOrderedAuthenticationMethods(AuthenticationState authenticationState, IEnumerable<IAuthenticationMethod> matchingAuthenticationMethods)
{
var skippedAuthenticationMethods = new List<IAuthenticationMethod>();

foreach (var authenticationMethod in matchingAuthenticationMethods)
{
if (authenticationState.ExecutedAuthenticationMethods.Contains(authenticationMethod))
{
skippedAuthenticationMethods.Add(authenticationMethod);
continue;
}

yield return authenticationMethod;
}

foreach (var authenticationMethod in skippedAuthenticationMethods)
yield return authenticationMethod;
}

private class AuthenticationState
{
private readonly IList<IAuthenticationMethod> _supportedAuthenticationMethods;

public AuthenticationState(IList<IAuthenticationMethod> supportedAuthenticationMethods)
{
_supportedAuthenticationMethods = supportedAuthenticationMethods;
ExecutedAuthenticationMethods = new List<IAuthenticationMethod>();
FailedAuthenticationMethods = new List<IAuthenticationMethod>();
}

/// <summary>
/// Gets the list of authentication methods that were previously executed.
/// </summary>
/// <value>
/// The list of authentication methods that were previously executed.
/// </value>
public IList<IAuthenticationMethod> ExecutedAuthenticationMethods { get; private set; }

/// <summary>
/// Gets the list of authentications methods that failed.
/// </summary>
/// <value>
/// The list of authentications methods that failed.
/// </value>
public IList<IAuthenticationMethod> FailedAuthenticationMethods { get; private set; }

/// <summary>
/// Gets the list of supported authentication methods.
/// </summary>
/// <value>
/// The list of supported authentication methods.
/// </value>
public IEnumerable<IAuthenticationMethod> SupportedAuthenticationMethods
{
get { return _supportedAuthenticationMethods; }
}
}
}
internal class ClientAuthentication
{
private int _maximumAuthTry = 50;

public int MaximumAuthTry
{
get { return _maximumAuthTry; }
set { _maximumAuthTry = value; }
}

public void Authenticate(IConnectionInfoInternal connectionInfo, ISession session)
{
if (connectionInfo == null)
throw new ArgumentNullException("connectionInfo");
if (session == null)
throw new ArgumentNullException("session");

session.RegisterMessage("SSH_MSG_USERAUTH_FAILURE");
session.RegisterMessage("SSH_MSG_USERAUTH_SUCCESS");
session.RegisterMessage("SSH_MSG_USERAUTH_BANNER");
session.UserAuthenticationBannerReceived += connectionInfo.UserAuthenticationBannerReceived;

try
{
// the exception to report an authentication failure with
SshAuthenticationException authenticationException = null;

// try to authenticate against none
var noneAuthenticationMethod = connectionInfo.CreateNoneAuthenticationMethod();

var authenticated = noneAuthenticationMethod.Authenticate(session);
if (authenticated != AuthenticationResult.Success)
{
if (!TryAuthenticate(session, new AuthenticationState(connectionInfo.AuthenticationMethods.ToList()), noneAuthenticationMethod.AllowedAuthentications.ToList(), ref authenticationException))
{
throw authenticationException;
}
}
}
finally
{
session.UserAuthenticationBannerReceived -= connectionInfo.UserAuthenticationBannerReceived;
session.UnRegisterMessage("SSH_MSG_USERAUTH_FAILURE");
session.UnRegisterMessage("SSH_MSG_USERAUTH_SUCCESS");
session.UnRegisterMessage("SSH_MSG_USERAUTH_BANNER");
}

}

private bool TryAuthenticate(ISession session,
AuthenticationState authenticationState,
ICollection<string> allowedAuthenticationMethods,
ref SshAuthenticationException authenticationException,
int tryCount = 0)
{
if (!allowedAuthenticationMethods.Any())
{
authenticationException = new SshAuthenticationException("No authentication methods defined on SSH server.");
return false;
}

// we want to try authentication methods in the order in which they were
// passed in the ctor, not the order in which the SSH server returns
// the allowed authentication methods
var matchingAuthenticationMethods = authenticationState.SupportedAuthenticationMethods.Where(a => allowedAuthenticationMethods.Contains(a.Name)).ToList();
if (!matchingAuthenticationMethods.Any())
{
authenticationException = new SshAuthenticationException(string.Format("No suitable authentication method found to complete authentication ({0}).", string.Join(",", allowedAuthenticationMethods.ToArray())));
return false;
}

foreach (var authenticationMethod in GetOrderedAuthenticationMethods(authenticationState, matchingAuthenticationMethods))
{
if (authenticationState.FailedAuthenticationMethods.Contains(authenticationMethod))
continue;

// when the authentication method was previously executed, then skip the authentication
// method as long as there's another authentication method to try; this is done to avoid
// a stack overflow for servers that do not update the list of allowed authentication
// methods after a partial success

if (!authenticationState.ExecutedAuthenticationMethods.Contains(authenticationMethod))
{
// update state to reflect previosuly executed authentication methods
authenticationState.ExecutedAuthenticationMethods.Add(authenticationMethod);
}

var authenticationResult = authenticationMethod.Authenticate(session);
switch (authenticationResult)
{
case AuthenticationResult.PartialSuccess:
if (tryCount > _maximumAuthTry)
{
authenticationException = new SshAuthenticationException(string.Format("Permission denied ({0}).", authenticationMethod.Name));
return false;
}
if (TryAuthenticate(session, authenticationState, authenticationMethod.AllowedAuthentications.ToList(), ref authenticationException, tryCount + 1))
{
authenticationResult = AuthenticationResult.Success;
}
break;
case AuthenticationResult.Failure:
authenticationState.FailedAuthenticationMethods.Add(authenticationMethod);
authenticationException = new SshAuthenticationException(string.Format("Permission denied ({0}).", authenticationMethod.Name));
break;
case AuthenticationResult.Success:
authenticationException = null;
break;
}

if (authenticationResult == AuthenticationResult.Success)
return true;
}

return false;
}

private IEnumerable<IAuthenticationMethod> GetOrderedAuthenticationMethods(AuthenticationState authenticationState, IEnumerable<IAuthenticationMethod> matchingAuthenticationMethods)
{
var skippedAuthenticationMethods = new List<IAuthenticationMethod>();

foreach (var authenticationMethod in matchingAuthenticationMethods)
{
if (authenticationState.ExecutedAuthenticationMethods.Contains(authenticationMethod))
{
skippedAuthenticationMethods.Add(authenticationMethod);
continue;
}

yield return authenticationMethod;
}

foreach (var authenticationMethod in skippedAuthenticationMethods)
yield return authenticationMethod;
}

private class AuthenticationState
{
private readonly IList<IAuthenticationMethod> _supportedAuthenticationMethods;

public AuthenticationState(IList<IAuthenticationMethod> supportedAuthenticationMethods)
{
_supportedAuthenticationMethods = supportedAuthenticationMethods;
ExecutedAuthenticationMethods = new List<IAuthenticationMethod>();
FailedAuthenticationMethods = new List<IAuthenticationMethod>();
}

/// <summary>
/// Gets the list of authentication methods that were previously executed.
/// </summary>
/// <value>
/// The list of authentication methods that were previously executed.
/// </value>
public IList<IAuthenticationMethod> ExecutedAuthenticationMethods { get; private set; }

/// <summary>
/// Gets the list of authentications methods that failed.
/// </summary>
/// <value>
/// The list of authentications methods that failed.
/// </value>
public IList<IAuthenticationMethod> FailedAuthenticationMethods { get; private set; }

/// <summary>
/// Gets the list of supported authentication methods.
/// </summary>
/// <value>
/// The list of supported authentication methods.
/// </value>
public IEnumerable<IAuthenticationMethod> SupportedAuthenticationMethods
{
get { return _supportedAuthenticationMethods; }
}
}
}
}
6 changes: 6 additions & 0 deletions TestConsole/TestConsole/App.config
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<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
</startup>
</configuration>
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