wslc: prevent session name squatting for default WSLc sessions by benhillis · Pull Request #40144 · microsoft/WSL

benhillis · 2026-04-09T16:23:33Z

Summary

Prevents malicious users from squatting reserved WSLc session names (wslc-cli, wslc-cli-admin) by moving default session name and settings resolution to the server.

Changes

Server-side default sessions: CreateSession(nullptr) and OpenSessionByName(nullptr) resolve the default session name from the caller's token. The client no longer knows or sends session names for default sessions.
Reserved name rejection: Explicit use of reserved names via CreateSession returns E_ACCESSDENIED.
Dedicated EnterSession API: Custom sessions (wslc session enter) use a separate API that reads settings.yaml server-side and sets NoCreate storage flags.
wslcsettings shared library: Extracted UserSettings into a shared library used by both wslc.exe and wslservice.exe. SettingsCommand now calls UserSettings directly instead of duplicating file creation logic.
Cleanup: Removed SessionOptions class, SessionModel.cpp, WslcSettingsTemplate.h. Moved EnumVariantMap.h to common. SessionSettings is NON_MOVABLE (uses unique_ptr to avoid c_str() pointer invalidation).

Testing

E2E test verifies reserved names are rejected and default session creation still works.
All 158 WSLCE2E tests pass (2 skipped).

Copilot

Copilot wasn't able to review this pull request because it exceeds the maximum number of files (300). Try reducing the number of changed files and requesting a review from Copilot again.

Copilot

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (2)

src/windows/wslc/services/SessionService.cpp:45

When attaching to the default session (empty sessionName -> nullptr passed to OpenSessionByName), failure paths still format errors using sessionName.c_str(), which is an empty string. This produces user-facing messages like "Session '' not found". Consider special-casing the empty-name/default-session case and emitting a clearer localized message (e.g., "Default session not found" / "Failed to open default session") instead of printing an empty name.

    HRESULT hr = manager->OpenSessionByName(sessionName.empty() ? nullptr : sessionName.c_str(), &session);
    if (FAILED(hr))
    {
        if (hr == HRESULT_FROM_WIN32(ERROR_NOT_FOUND))
        {
            wslutil::PrintMessage(Localization::MessageWslcSessionNotFound(sessionName.c_str()), stderr);
            return 1;
        }

        auto errorString = wsl::windows::common::wslutil::ErrorCodeToString(hr);
        wslutil::PrintMessage(
            Localization::MessageErrorCode(Localization::MessageWslcOpenSessionFailed(sessionName.c_str()), errorString), stderr);
        return 1;

src/windows/wslc/services/SessionService.cpp:186

TerminateSession now treats an empty displayName as "default session" (nullptr passed to OpenSessionByName), but the "not found" / "terminate failed" messages still use displayName.c_str() and can end up printing an empty name. Please special-case the default-session call path so the error message is meaningful when no session name was provided.

    wil::com_ptr<IWSLCSession> session;
    HRESULT hr = sessionManager->OpenSessionByName(displayName.empty() ? nullptr : displayName.c_str(), &session);
    if (FAILED(hr))
    {
        if (hr == HRESULT_FROM_WIN32(ERROR_NOT_FOUND))
        {
            wslutil::PrintMessage(Localization::MessageWslcSessionNotFound(displayName.c_str()), stderr);
            return 1;
        }

src/windows/service/exe/WSLCSessionManager.cpp

test/windows/wslc/e2e/WSLCE2ESessionEnterTests.cpp

Copilot

Pull request overview

Copilot reviewed 24 out of 25 changed files in this pull request and generated 1 comment.

src/windows/common/CMakeLists.txt

Copilot

Pull request overview

Copilot reviewed 24 out of 25 changed files in this pull request and generated 5 comments.

src/windows/service/inc/wslc.idl

src/windows/service/exe/WSLCSessionManager.cpp

src/windows/common/CMakeLists.txt

test/windows/wslc/e2e/WSLCE2EGlobalTests.cpp

Copilot

Pull request overview

Copilot reviewed 24 out of 25 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

src/windows/common/WSLCUserSettings.cpp:12

File header comment still says Module Name: UserSettings.cpp, but the file is now WSLCUserSettings.cpp. Please update the module name to match the actual filename to avoid confusion when tracing build/log output and code ownership.

Copilot · 2026-04-10T02:27:47Z

src/windows/service/exe/WSLCSessionManager.cpp

@@ -88,6 +167,14 @@ void WSLCSessionManagerImpl::CreateSession(const WSLCSessionSettings* Settings,

    wslutil::StopWatch stopWatch;

+    // Initialize settings for the default session.
+    std::unique_ptr<SessionSettings> defaultSettings;
+    if (Settings == nullptr)
+    {
+        defaultSettings = SessionSettings::Default(callerToken.get(), tokenInfo.Elevated);
+        Settings = &defaultSettings->Settings;
+    }


CreateSession holds m_wslcSessionsLock while loading/parsing user settings (YAML) for default sessions (SessionSettings::Default(...)). This introduces file I/O and YAML parsing under the session manager lock, which can block other session operations and increase contention. Consider building the resolved/default SessionSettings outside the lock (or caching per-user settings) and only holding the lock for the session lookup/mutation portion.

Copilot · 2026-04-10T02:27:47Z

localization/strings/en-US/Resources.resw

+  <data name="MessageWslcDefaultSessionNotFound" xml:space="preserve">
+    <value>Default session not found</value>
+  </data>
+  <data name="MessageWslcOpenDefaultSessionFailed" xml:space="preserve">
+    <value>Failed to open default session</value>
+  </data>
+  <data name="MessageWslcTerminateDefaultSessionFailed" xml:space="preserve">
+    <value>Default session termination failed</value>
+  </data>


New user-facing resource keys were added only to en-US/Resources.resw. Other locales currently lack these entries (the localization validator only warns), which can cause missing translations/fallback-to-English behavior for non-en-US users. Consider adding placeholder entries for these keys in the other locale .resw files so localization can pick them up consistently.

- Server now determines default session name and settings from caller's token, preventing malicious users from squatting reserved session names - CreateSession rejects explicit use of reserved names (wslc-cli, wslc-cli-admin) with E_ACCESSDENIED - Null StoragePath remains valid for ephemeral sessions; empty string is rejected as E_INVALIDARG - Add dedicated EnterSession API for custom sessions - Extract UserSettings into shared wslcsettings library used by both wslc.exe and wslservice.exe - Move EnumVariantMap.h to common - wslc.exe no longer parses settings.yaml; service handles all config - Fix std::terminate crash in CustomDmesgOutput test when CreateSession fails by adding a scope_exit guard to join the reader thread - Add session name squatting E2E test

Copilot AI review requested due to automatic review settings April 9, 2026 16:23

Copilot AI reviewed Apr 9, 2026

View reviewed changes

benhillis changed the base branch from master to feature/wsl-for-apps April 9, 2026 16:26

benhillis requested a review from Copilot April 9, 2026 16:26

Copilot started reviewing on behalf of benhillis April 9, 2026 16:28 View session

Copilot AI reviewed Apr 9, 2026

View reviewed changes

src/windows/service/exe/WSLCSessionManager.cpp Show resolved Hide resolved

test/windows/wslc/e2e/WSLCE2ESessionEnterTests.cpp Outdated Show resolved Hide resolved

benhillis force-pushed the user/benhill/wslc_default_session branch from 6df494e to c991c9d Compare April 9, 2026 22:50

Copilot AI review requested due to automatic review settings April 9, 2026 22:54

benhillis force-pushed the user/benhill/wslc_default_session branch from c991c9d to 46d783e Compare April 9, 2026 22:54

Copilot started reviewing on behalf of benhillis April 9, 2026 22:54 View session

Copilot AI reviewed Apr 9, 2026

View reviewed changes

src/windows/common/CMakeLists.txt Outdated Show resolved Hide resolved

benhillis force-pushed the user/benhill/wslc_default_session branch 2 times, most recently from 46c11a9 to 7cb7ef9 Compare April 10, 2026 00:31

Copilot AI review requested due to automatic review settings April 10, 2026 00:31

Copilot started reviewing on behalf of benhillis April 10, 2026 00:32 View session

benhillis force-pushed the user/benhill/wslc_default_session branch from 7cb7ef9 to 784b41f Compare April 10, 2026 00:34

Copilot AI reviewed Apr 10, 2026

View reviewed changes

benhillis force-pushed the user/benhill/wslc_default_session branch from 784b41f to d0b3819 Compare April 10, 2026 02:12

benhillis changed the title ~~Prevent session name squatting for default WSLc sessions~~ wslc: prevent session name squatting for default WSLc sessions Apr 10, 2026

benhillis marked this pull request as ready for review April 10, 2026 02:22

benhillis requested a review from a team as a code owner April 10, 2026 02:22

Copilot AI review requested due to automatic review settings April 10, 2026 02:22

Copilot started reviewing on behalf of benhillis April 10, 2026 02:23 View session

Copilot AI reviewed Apr 10, 2026

View reviewed changes

benhillis force-pushed the user/benhill/wslc_default_session branch from d0b3819 to 50b93fb Compare April 10, 2026 02:50

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

wslc: prevent session name squatting for default WSLc sessions#40144

wslc: prevent session name squatting for default WSLc sessions#40144
benhillis wants to merge 1 commit intofeature/wsl-for-appsfrom
user/benhill/wslc_default_session

benhillis commented Apr 9, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Apr 10, 2026

Uh oh!

Copilot AI Apr 10, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

benhillis commented Apr 9, 2026

Summary

Changes

Testing

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Apr 10, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Apr 10, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants