Revert Windows service check refactoring, and replace with a different fix.

This reverts commit 38bdba54a6, "Fix and
simplify check for whether we're running as Windows service". It turns out
that older versions of MinGW - like that on buildfarm member narwhal - do
not support the CheckTokenMembership() function. This replaces the
refactoring with a much smaller fix, to add a check for SE_GROUP_ENABLED to
pgwin32_is_service().

Only apply to back-branches, and keep the refactoring in HEAD. It's
unlikely that anyone is still really using such an old version of MinGW -
aside from narwhal - but let's not change the minimum requirements in
minor releases.

Discussion: https://www.postgresql.org/message-id/16609.1489773427@sss.pgh.pa.us
Patch: https://www.postgresql.org/message-id/CAB7nPqSvfu%3DKpJ%3DNX%2BYAHmgAmQdzA7N5h31BjzXeMgczhGCC%2BQ%40mail.gmail.com

src/backend/port/win32/security.c

@@ -14,6 +14,10 @@
 #include "postgres.h"
 
 
+static BOOL pgwin32_get_dynamic_tokeninfo(HANDLE token,
+							TOKEN_INFORMATION_CLASS class, char **InfoBuffer,
+							  char *errbuf, int errsize);
+
 /*
  * Returns nonzero if the current user has administrative privileges,
  * or zero if not.
@@ -24,11 +28,33 @@
 int
 pgwin32_is_admin(void)
 {
+	HANDLE		AccessToken;
+	char	   *InfoBuffer = NULL;
+	char		errbuf[256];
+	PTOKEN_GROUPS Groups;
 	PSID		AdministratorsSid;
 	PSID		PowerUsersSid;
 	SID_IDENTIFIER_AUTHORITY NtAuthority = {SECURITY_NT_AUTHORITY};
-	BOOL		IsAdministrators;
+	UINT		x;
-	BOOL		IsPowerUsers;
+	BOOL		success;
+
+	if (!OpenProcessToken(GetCurrentProcess(), TOKEN_READ, &AccessToken))
+	{
+		write_stderr("could not open process token: error code %lu\n",
+					 GetLastError());
+		exit(1);
+	}
+
+	if (!pgwin32_get_dynamic_tokeninfo(AccessToken, TokenGroups,
+									   &InfoBuffer, errbuf, sizeof(errbuf)))
+	{
+		write_stderr("%s", errbuf);
+		exit(1);
+	}
+
+	Groups = (PTOKEN_GROUPS) InfoBuffer;
+
+	CloseHandle(AccessToken);
 
 	if (!AllocateAndInitializeSid(&NtAuthority, 2,
 		 SECURITY_BUILTIN_DOMAIN_RID, DOMAIN_ALIAS_RID_ADMINS, 0, 0, 0, 0, 0,
@@ -48,35 +74,32 @@ pgwin32_is_admin(void)
 		exit(1);
 	}
 
-	if (!CheckTokenMembership(NULL, AdministratorsSid, &IsAdministrators) ||
+	success = FALSE;
-		!CheckTokenMembership(NULL, PowerUsersSid, &IsPowerUsers))
+
+	for (x = 0; x < Groups->GroupCount; x++)
 	{
-		write_stderr("could not check access token membership: error code %lu\n",
+		if ((EqualSid(AdministratorsSid, Groups->Groups[x].Sid) && (Groups->Groups[x].Attributes & SE_GROUP_ENABLED)) ||
-					 GetLastError());
+			(EqualSid(PowerUsersSid, Groups->Groups[x].Sid) && (Groups->Groups[x].Attributes & SE_GROUP_ENABLED)))
-		exit(1);
+		{
+			success = TRUE;
+			break;
+		}
 	}
 
+	free(InfoBuffer);
 	FreeSid(AdministratorsSid);
 	FreeSid(PowerUsersSid);
-
+	return success;
-	if (IsAdministrators || IsPowerUsers)
-		return 1;
-	else
-		return 0;
 }
 
 /*
  * We consider ourselves running as a service if one of the following is
  * true:
  *
- * 1) We are running as LocalSystem (only used by services)
+ * 1) We are running as Local System (only used by services)
  * 2) Our token contains SECURITY_SERVICE_RID (automatically added to the
  *	  process token by the SCM when starting a service)
  *
- * The check for LocalSystem is needed, because surprisingly, if a service
- * is running as LocalSystem, it does not have SECURITY_SERVICE_RID in its
- * process token.
- *
  * Return values:
  *	 0 = Not service
  *	 1 = Service
@@ -90,62 +113,137 @@ int
 pgwin32_is_service(void)
 {
 	static int	_is_service = -1;
-	BOOL		IsMember;
+	HANDLE		AccessToken;
+	char	   *InfoBuffer = NULL;
+	char		errbuf[256];
+	PTOKEN_GROUPS Groups;
+	PTOKEN_USER User;
 	PSID		ServiceSid;
 	PSID		LocalSystemSid;
 	SID_IDENTIFIER_AUTHORITY NtAuthority = {SECURITY_NT_AUTHORITY};
+	UINT		x;
 
 	/* Only check the first time */
 	if (_is_service != -1)
 		return _is_service;
 
-	/* First check for LocalSystem */
+	if (!OpenProcessToken(GetCurrentProcess(), TOKEN_READ, &AccessToken))
+	{
+		fprintf(stderr, "could not open process token: error code %lu\n",
+				GetLastError());
+		return -1;
+	}
+
+	/* First check for local system */
+	if (!pgwin32_get_dynamic_tokeninfo(AccessToken, TokenUser, &InfoBuffer,
+									   errbuf, sizeof(errbuf)))
+	{
+		fprintf(stderr, "%s", errbuf);
+		return -1;
+	}
+
+	User = (PTOKEN_USER) InfoBuffer;
+
 	if (!AllocateAndInitializeSid(&NtAuthority, 1,
 							  SECURITY_LOCAL_SYSTEM_RID, 0, 0, 0, 0, 0, 0, 0,
 								  &LocalSystemSid))
 	{
 		fprintf(stderr, "could not get SID for local system account\n");
+		CloseHandle(AccessToken);
 		return -1;
 	}
 
-	if (!CheckTokenMembership(NULL, LocalSystemSid, &IsMember))
+	if (EqualSid(LocalSystemSid, User->User.Sid))
 	{
-		fprintf(stderr, "could not check access token membership: error code %lu\n",
-				GetLastError());
 		FreeSid(LocalSystemSid);
-		return -1;
+		free(InfoBuffer);
-	}
+		CloseHandle(AccessToken);
-	FreeSid(LocalSystemSid);
-
-	if (IsMember)
-	{
 		_is_service = 1;
 		return _is_service;
 	}
 
-	/* Check for service group membership */
+	FreeSid(LocalSystemSid);
+	free(InfoBuffer);
+
+	/* Now check for group SID */
+	if (!pgwin32_get_dynamic_tokeninfo(AccessToken, TokenGroups, &InfoBuffer,
+									   errbuf, sizeof(errbuf)))
+	{
+		fprintf(stderr, "%s", errbuf);
+		return -1;
+	}
+
+	Groups = (PTOKEN_GROUPS) InfoBuffer;
+
 	if (!AllocateAndInitializeSid(&NtAuthority, 1,
 								  SECURITY_SERVICE_RID, 0, 0, 0, 0, 0, 0, 0,
 								  &ServiceSid))
 	{
-		fprintf(stderr, "could not get SID for service group: error code %lu\n",
+		fprintf(stderr, "could not get SID for service group\n");
-				GetLastError());
+		free(InfoBuffer);
+		CloseHandle(AccessToken);
 		return -1;
 	}
 
-	if (!CheckTokenMembership(NULL, ServiceSid, &IsMember))
+	_is_service = 0;
+	for (x = 0; x < Groups->GroupCount; x++)
 	{
-		fprintf(stderr, "could not check access token membership: error code %lu\n",
+		if (EqualSid(ServiceSid, Groups->Groups[x].Sid) &&
-				GetLastError());
+			(Groups->Groups[x].Attributes & SE_GROUP_ENABLED))
-		FreeSid(ServiceSid);
+		{
-		return -1;
+			_is_service = 1;
+			break;
+		}
 	}
+
+	free(InfoBuffer);
 	FreeSid(ServiceSid);
 
-	if (IsMember)
+	CloseHandle(AccessToken);
-		_is_service = 1;
-	else
-		_is_service = 0;
 
 	return _is_service;
 }
+
+
+/*
+ * Call GetTokenInformation() on a token and return a dynamically sized
+ * buffer with the information in it. This buffer must be free():d by
+ * the calling function!
+ */
+static BOOL
+pgwin32_get_dynamic_tokeninfo(HANDLE token, TOKEN_INFORMATION_CLASS class,
+							  char **InfoBuffer, char *errbuf, int errsize)
+{
+	DWORD		InfoBufferSize;
+
+	if (GetTokenInformation(token, class, NULL, 0, &InfoBufferSize))
+	{
+		snprintf(errbuf, errsize, "could not get token information: got zero size\n");
+		return FALSE;
+	}
+
+	if (GetLastError() != ERROR_INSUFFICIENT_BUFFER)
+	{
+		snprintf(errbuf, errsize, "could not get token information: error code %lu\n",
+				 GetLastError());
+		return FALSE;
+	}
+
+	*InfoBuffer = malloc(InfoBufferSize);
+	if (*InfoBuffer == NULL)
+	{
+		snprintf(errbuf, errsize, "could not allocate %d bytes for token information\n",
+				 (int) InfoBufferSize);
+		return FALSE;
+	}
+
+	if (!GetTokenInformation(token, class, *InfoBuffer,
+							 InfoBufferSize, &InfoBufferSize))
+	{
+		snprintf(errbuf, errsize, "could not get token information: error code %lu\n",
+				 GetLastError());
+		return FALSE;
+	}
+
+	return TRUE;
+}