Keep the shell server's basic user journey working
The cleanup job now restores the whole home directory instead of only the four text files: the directory itself, the shell configuration that gives the prompt, and the files. Anything that is not a regular file is replaced, so the files stay text files. The README in server/ describes the security model: the box is a disposable VPS that may be compromised, the root user may do whatever they want, and only the prompt, the home directory and the four files are kept working. Co-Authored-By: Claude Code <noreply@anthropic.com>
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Zebreus
parent
54607982cf
commit
23896bced5
1 changed files with 165 additions and 35 deletions
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@ -1,6 +1,6 @@
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# Installs the scheduled task that puts the shell server's README and Code of Conduct files back every 30
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# minutes. The task runs as SYSTEM, so the shell server's root user can neither stop it nor change the copies it
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# restores from.
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# Installs the scheduled task that puts the shell server's home directory back into shape every 30 minutes: the
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# prompt, the home directory and the four text files. The task runs as SYSTEM, so the shell server's root user can
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# neither stop it nor change the copies it restores from.
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#
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# Run this in an elevated PowerShell on the server, with this script and the ../resources directory next to it:
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# powershell -ExecutionPolicy Bypass -File .\install_restore_task.ps1
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@ -8,36 +8,83 @@
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# powershell -ExecutionPolicy Bypass -File .\install_restore_task.ps1 -Uninstall
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[CmdletBinding()]
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param(
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[string]$Target = 'C:\msys2\home\root',
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[string]$HomeDir = 'C:\msys2\home\root',
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[switch]$Uninstall
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)
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$ErrorActionPreference = 'Stop'
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$installDir = 'C:\ProgramData\kik-restore'
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$copiesDir = Join-Path $installDir 'files'
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$taskName = 'KiK restore shell files'
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$files = 'README', 'README.en', 'CODE_OF_CONDUCT', 'CODE_OF_CONDUCT.en'
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# The copies the task restores from and the script it runs both live in $installDir, which only SYSTEM and the
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# administrators may read or write.
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$restoreScript = @'
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# Puts the shell server's README and Code of Conduct files back from the copies next to this script.
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# Runs as SYSTEM every 30 minutes; the shell server's root user can neither stop it nor change the copies.
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param([string]$Target = 'C:\msys2\home\root')
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# Puts the shell server's home directory back into shape: the directory itself, the shell configuration that gives
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# the prompt, and the four text files. Runs as SYSTEM every 30 minutes; the shell server's root user can neither stop
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# it nor change the copies it restores from.
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param([string]$HomeDir = 'C:\msys2\home\root')
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$log = Join-Path $PSScriptRoot 'restore.log'
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$copies = Join-Path $PSScriptRoot 'files'
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foreach ($name in @('README', 'README.en', 'CODE_OF_CONDUCT', 'CODE_OF_CONDUCT.en')) {
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$path = Join-Path $Target $name
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# The account of the shell server's root user, whose id the files in its home directory belong to.
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$passwd = Get-Content 'C:\msys2\etc\passwd' -ErrorAction SilentlyContinue | Where-Object { $_ -like 'root:*' }
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$sid = if ($passwd) { ($passwd -split ':')[4].Split(',')[-1] }
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function Write-Log($message) {
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"$(Get-Date -Format s) $message" | Out-File -FilePath $log -Append
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}
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# Removes a file, a directory or a link, but never what a link points to.
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function Remove-Anything($path) {
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$item = Get-Item -LiteralPath $path -Force
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if ($item.Attributes -band [IO.FileAttributes]::ReparsePoint) {
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if ($item.PSIsContainer) { [IO.Directory]::Delete($path) } else { [IO.File]::Delete($path) }
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} elseif ($item.PSIsContainer) {
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Remove-Item -LiteralPath $path -Recurse -Force
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} else {
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Remove-Item -LiteralPath $path -Force
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}
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}
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# The home directory is the one from /etc/passwd, which the user cannot change, but which they can delete.
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function New-Home($path) {
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New-Item -ItemType Directory -Path $path | Out-Null
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# The parent directory gives the users read access only, so the owner gets write access on their own home.
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if ($sid) {
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icacls $path /grant "*${sid}:(OI)(CI)F" | Out-Null
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icacls $path /setowner "*$sid" | Out-Null
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}
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}
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if (-not (Test-Path -LiteralPath $HomeDir)) {
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New-Home $HomeDir
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Write-Log "created $HomeDir"
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} elseif ((Get-Item -LiteralPath $HomeDir -Force).Attributes -band [IO.FileAttributes]::ReparsePoint) {
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Remove-Anything $HomeDir
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New-Home $HomeDir
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Write-Log "replaced the link $HomeDir"
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}
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foreach ($copy in Get-ChildItem -LiteralPath $copies -File -Force) {
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$target = Join-Path $HomeDir $copy.Name
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try {
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if (Test-Path -LiteralPath $path) {
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# the root user may have replaced the file or locked everyone else out
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takeown /f $path /a | Out-Null
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icacls $path /reset | Out-Null
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if ((Get-Item -LiteralPath $path -Force).PSIsContainer) { Remove-Item -LiteralPath $path -Recurse -Force }
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if (Test-Path -LiteralPath $target) {
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$item = Get-Item -LiteralPath $target -Force
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if ($item.PSIsContainer -or $item.Attributes -band [IO.FileAttributes]::ReparsePoint) {
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# anything but a file is replaced, so that the files are always the text files they should be
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Remove-Anything $target
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} else {
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# the user may have locked the file; taking it back lets us write it
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takeown /f $target /a | Out-Null
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icacls $target /reset | Out-Null
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}
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}
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Copy-Item -LiteralPath (Join-Path $PSScriptRoot $name) -Destination $path -Force
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"$(Get-Date -Format s) restored $name" | Out-File -FilePath $log -Append
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Copy-Item -LiteralPath $copy.FullName -Destination $target -Force
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if ($sid) { icacls $target /setowner "*$sid" | Out-Null }
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Write-Log "restored $($copy.Name)"
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} catch {
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"$(Get-Date -Format s) failed $name : $_" | Out-File -FilePath $log -Append
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Write-Log "failed $($copy.Name) : $_"
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}
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}
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'@
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@ -54,14 +101,13 @@ if ($Uninstall) {
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}
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$resources = Join-Path $PSScriptRoot '..\resources'
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$missing = $files | Where-Object { -not (Test-Path -LiteralPath (Join-Path $resources $_)) }
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if ($missing) { throw "Missing files in $resources : $($missing -join ', ')" }
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if (-not (Get-ChildItem -LiteralPath $resources -File -Force)) { throw "No files in $resources." }
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# The root user may have prepared the directory or the file names, so nothing that looks like a link is used.
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$prepared = Get-Item -LiteralPath $installDir -Force -ErrorAction SilentlyContinue
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if ($prepared -and $prepared.Attributes -band [IO.FileAttributes]::ReparsePoint) { throw "$installDir is a link, refusing to install." }
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New-Item -ItemType Directory -Force -Path $installDir | Out-Null
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New-Item -ItemType Directory -Force -Path $copiesDir | Out-Null
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# Only SYSTEM and the administrators may read or write the copies and the script.
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$acl = New-Object System.Security.AccessControl.DirectorySecurity
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@ -73,18 +119,18 @@ $acl.SetOwner((New-Object System.Security.Principal.SecurityIdentifier 'S-1-5-32
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Set-Acl -LiteralPath $installDir -AclObject $acl
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# Files the root user prepared are removed, the copies are written fresh and inherit the restricted permissions.
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foreach ($name in $files + 'restore.ps1') {
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$path = Join-Path $installDir $name
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foreach ($copy in Get-ChildItem -LiteralPath $resources -File -Force) {
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$path = Join-Path $copiesDir $copy.Name
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if (Test-Path -LiteralPath $path) {
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$item = Get-Item -LiteralPath $path -Force
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if ($item.Attributes -band [IO.FileAttributes]::ReparsePoint) { throw "$path is a link, refusing to install." }
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Remove-Item -LiteralPath $path -Recurse -Force
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}
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Copy-Item -LiteralPath $copy.FullName -Destination $path -Force
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}
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Copy-Item -Path (Join-Path $resources '*') -Destination $installDir -Force
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[IO.File]::WriteAllText((Join-Path $installDir 'restore.ps1'), $restoreScript)
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$action = New-ScheduledTaskAction -Execute 'powershell.exe' -Argument "-NoProfile -NonInteractive -ExecutionPolicy Bypass -WindowStyle Hidden -File `"$installDir\restore.ps1`" -Target `"$Target`""
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$action = New-ScheduledTaskAction -Execute 'powershell.exe' -Argument "-NoProfile -NonInteractive -ExecutionPolicy Bypass -WindowStyle Hidden -File `"$installDir\restore.ps1`" -HomeDir `"$HomeDir`""
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$triggers = @(
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New-ScheduledTaskTrigger -Once -At (Get-Date) -RepetitionInterval (New-TimeSpan -Minutes 30) -RepetitionDuration (New-TimeSpan -Days 3650)
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New-ScheduledTaskTrigger -AtStartup
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@ -97,5 +143,5 @@ Start-ScheduledTask -TaskName $taskName
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Start-Sleep -Seconds 5
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Write-Host "Task '$taskName' runs as SYSTEM every 30 minutes and at startup."
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Get-ScheduledTaskInfo -TaskName $taskName | Format-List LastRunTime, LastTaskResult, NextRunTime
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Get-Content (Join-Path $installDir 'restore.log') -Tail 4 -ErrorAction SilentlyContinue
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Get-Content (Join-Path $installDir 'restore.log') -Tail 8 -ErrorAction SilentlyContinue
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icacls $installDir
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