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IsSystemdService: make check stricter to avoid false positives #2734

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Merged
halter73 merged 1 commit into from
Dec 4, 2019
Merged

IsSystemdService: make check stricter to avoid false positives #2734

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24 changes: 3 additions & 21 deletions src/Hosting/Systemd/src/SystemdHelpers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,46 +14,28 @@ namespace Microsoft.Extensions.Hosting.Systemd
/// </summary>
public static class SystemdHelpers
{
private const string INVOCATION_ID = "INVOCATION_ID";

private static bool? _isSystemdService;

/// <summary>
/// Check if the current process is hosted as a systemd Service.
/// </summary>
/// <returns><c>True</c> if the current process is hosted as a systemd Service, otherwise <c>false</c>.</returns>
public static bool IsSystemdService()
=> _isSystemdService ?? (bool)(_isSystemdService = CheckSystemdUnit());
=> _isSystemdService ?? (bool)(_isSystemdService = CheckParentIsSystemd());

private static bool CheckSystemdUnit()
private static bool CheckParentIsSystemd()
{
// No point in testing anything unless it's Unix
if (Environment.OSVersion.Platform != PlatformID.Unix)
{
return false;
}

// We've got invocation id, it's systemd >= 232 running a unit (either directly or through a child process)
if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable(INVOCATION_ID)))
{
return true;
}

// Either it's not a unit, or systemd is < 232, do a bit more digging
try
{
// Test parent process (this matches only direct parents, walking all the way up to the PID 1 is probably not what we would want)
// Check whether our direct parent is 'systemd'.
var parentPid = GetParentPid();
var ppidString = parentPid.ToString(NumberFormatInfo.InvariantInfo);

// If parent PID is not 1, this may be a user unit, in this case it must match MANAGERPID envvar
if (parentPid != 1
&& Environment.GetEnvironmentVariable("MANAGERPID") != ppidString)
{
return false;
}

// Check parent process name to match "systemd\n"
var comm = File.ReadAllBytes("/proc/" + ppidString + "/comm");
return comm.AsSpan().SequenceEqual(Encoding.ASCII.GetBytes("systemd\n"));
}
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