Reject non-empty directories for new WSLC session storage by beena352 · Pull Request #40655 · microsoft/WSL

beena352 · 2026-05-27T17:35:41Z

Summary of the Pull Request

Prevent users from accidentally reusing existing non-empty directories as WSLC session storage. For new sessions, validate that the storage directory is either empty or non-existent. Existing sessions identified by their storage.vhdx VHD bypass this check, so users can re-enter sessions freely even if additional files are present in the storage directory.

PR Checklist

Closes: Link to issue #62259817
Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
Tests: Added/updated if needed and all pass
Localization: All end user facing strings can be localized
Dev docs: Added/updated if needed
Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validate session storage paths at initialization time:

If creating a new session and the directory already exists and is non-empty, reject with E_INVALIDARG and a user-facing error message
If the directory is empty or doesn't exist, create it and proceed
If a session's VHD already exists in the directory, skip the emptiness check (re-entry allowed)
This prevents data loss by ensuring new sessions don't accidentally overwrite unrelated user files placed in the storage directory. Once a session is created (VHD exists), the directory can contain other files without blocking re-entry.

Validation Steps Performed

Copilot

Pull request overview

Adds a wslcsession marker-file convention at the root of a WSLC session storage directory so the service can distinguish directories it owns from arbitrary user content, and rejects new session creation into a non-empty, unmarked directory. Also wires IErrorInfo/COMServiceExecutionContext through the per-user WSLCSessionFactory and WSLCSessionManager so the user-facing rejection message reaches the CLI/test caller.

Changes:

Add EnsureSessionMarker helper in WSLCSession::ConfigureStorage (new sessions require empty dir + stamp marker; existing VHD paths get a legacy upgrade stamp).
Add ISupportErrorInfo + COMServiceExecutionContext to WSLCSessionFactory and propagate IErrorInfo from factory to caller in WSLCSessionManagerImpl::CreateSession; add ISupportErrorInfo to WSLCSessionManager.
Add API-level and e2e tests for marker rejection and legacy auto-upgrade; add localized MessageWslcSessionStorageMustBeEmpty.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/windows/wslcsession/WSLCSession.cpp	New `EnsureSessionMarker` helper and wiring into `ConfigureStorage` for new/existing storage paths.
src/windows/wslcsession/WSLCSessionFactory.cpp	Establish `COMServiceExecutionContext` around `CreateSession` and implement `InterfaceSupportsErrorInfo`.
src/windows/wslcsession/WSLCSessionFactory.h	Add `ISupportErrorInfo` base and method declaration.
src/windows/service/exe/WSLCSessionManager.cpp	Inspect `IErrorInfo` after factory failure and re-throw with user-facing message; implement `InterfaceSupportsErrorInfo`.
src/windows/service/exe/WSLCSessionManager.h	Add `ISupportErrorInfo` base and method declaration.
test/windows/WSLCTests.cpp	New API-level cases: non-empty dir rejection and `wslcsession`-as-directory rejection with COM error validation.
test/windows/wslc/e2e/WSLCE2ESessionEnterTests.cpp	E2E test verifying marker creation on default session and legacy auto-upgrade.
localization/strings/en-US/Resources.resw	New `MessageWslcSessionStorageMustBeEmpty` localized string.

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

OneBlue

I think refusing to create a session storage if the directory is non-empty makes sense (although I worry a bit about this putting us in a corner, like if there's ever a thumdb.db, desktop.ini or similar file created, this could "lock a user out" of using that folder permanently)

I'm not sure about the marker file though. Whenever we create a storage folder, we always create a storage VHD, so could we use that directly instead ?

…slc-session-storage-marker

…eenachauhan/wslc-session-storage-marker

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

…ew sessions

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Add marker-file validation for WSLC session storage

7b5b423

Copilot AI review requested due to automatic review settings May 27, 2026 17:35

Copilot started reviewing on behalf of beena352 May 27, 2026 17:35 View session

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beena352 requested a review from Copilot May 27, 2026 17:44

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beena352 added 2 commits May 27, 2026 20:37

Fix CreateSessionValidation test

d88f735

fix test

ba8a228

Copilot AI review requested due to automatic review settings May 28, 2026 16:36

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simplify comments and guard is_empty error check

81268fa

OneBlue reviewed May 29, 2026

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beena352 added 2 commits May 29, 2026 14:41

Merge remote-tracking branch 'origin/master' into user/beenachauhan/w…

5762bb3

…slc-session-storage-marker

Merge branch 'master' of https://github.com/microsoft/WSL into user/b…

e5aa1ba

…eenachauhan/wslc-session-storage-marker

Copilot AI review requested due to automatic review settings June 2, 2026 18:53

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Comment thread src/windows/wslcsession/WSLCSession.cpp Outdated

Comment thread src/windows/wslcsession/WSLCSession.cpp

Comment thread src/windows/wslcsession/WSLCSessionFactory.cpp Outdated

Prevent session storage reuse by validating directory emptiness for n…

48ed435

…ew sessions

beena352 requested a review from Copilot June 3, 2026 03:39

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Comment thread src/windows/wslcsession/WSLCSession.cpp

Use error_code overload for creating storage directories

8c99886

beena352 requested a review from Copilot June 3, 2026 04:13

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Comment thread src/windows/wslcsession/WSLCSessionFactory.cpp Outdated

beena352 marked this pull request as ready for review June 3, 2026 17:40

beena352 requested a review from a team as a code owner June 3, 2026 17:40

beena352 marked this pull request as draft June 3, 2026 17:41

beena352 changed the title ~~Add marker-file validation for WSLC session storage~~ Reject non-empty directories for new WSLC session storage Jun 3, 2026

beena352 marked this pull request as ready for review June 3, 2026 17:43

beena352 marked this pull request as draft June 4, 2026 22:18

resolve conflict

d8f44ff

beena352 requested a review from Copilot June 4, 2026 23:20

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Comment thread src/windows/wslcsession/WSLCSession.cpp

beena352 added 2 commits June 5, 2026 08:43

Validate that session storage path is a directory, not a file

b3b908b

Format

61a3c6b

beena352 requested a review from Copilot June 5, 2026 15:46

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Comment thread src/windows/wslcsession/WSLCSession.cpp

beena352 marked this pull request as ready for review June 5, 2026 16:12

Restore defensive create_directories call before VHD creation

45b2731

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Reject non-empty directories for new WSLC session storage#40655

Reject non-empty directories for new WSLC session storage#40655
beena352 wants to merge 12 commits into
microsoft:masterfrom
beena352:user/beenachauhan/wslc-session-storage-marker

beena352 commented May 27, 2026 •

edited

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beena352 commented May 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary of the Pull Request

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beena352 commented May 27, 2026 •

edited

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