* syscalls.cc (seteuid): Set default dacl in process token.

Replace in-line code by call to verify_token().
	(setegid): Reverse change from 2002-01-21. Add call to
	RevertToSelf and set primary group in impersonation token.
	* security.cc (create_token): Store pgrpsid in token security
	descriptor, except if it already appears in my_grps.
	Use sec_acl() in place of get_dacl().
	(verify_token): Create from code in seteuid(), with tighter checks.
	(get_dacl) Deleted.
	(get_group_sidlist): Add argument to indicate if pgrpsid is already
	in the groups.
	* security.h: Define verify_token().
	* autoload.cc: Load GetKernelObjectSecurity().

winsup/cygwin/security.h

@@ -181,6 +181,8 @@ void set_security_attribute (int attribute, PSECURITY_ATTRIBUTES psa,
 HANDLE subauth (struct passwd *pw);
 /* Try creating a token directly. */
 HANDLE create_token (cygsid &usersid, cygsid &pgrpsid);
+/* Verify an existing token */
+BOOL verify_token (HANDLE token, cygsid &usersid, cygsid &pgrpsid, BOOL * pintern = NULL);
 
 /* Extract U-domain\user field from passwd entry. */
 void extract_nt_dom_user (const struct passwd *pw, char *domain, char *user);