bug#10021: [PATCH id] Add error-checking on GNU

[Paul Eggert]

I found yet-another tricky bug in that id.c code,
and fixed it as follows:

>From 5ca593e87eb1361b4696dd1e002a8ee310a5d1f6 Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Tue, 15 Nov 2011 13:23:24 -0800
Subject: [PATCH] id: fix bug when euid != ruid

* src/id.c (main): Report an error if no args are given and getuid
fails, because print_full_info needs ruid.  Redo code so that
getuid and friends are invoked only when needed; this makes the
code easier to follow, and is how I found the above bug.
---
 src/id.c |   51 ++++++++++++++++++++++++++++++---------------------
 1 files changed, 30 insertions(+), 21 deletions(-)

diff --git a/src/id.c b/src/id.c
index 8f7ce9e..1047149 100644
--- a/src/id.c
+++ b/src/id.c
@@ -207,27 +207,36 @@ main (int argc, char **argv)
       uid_t NO_UID = -1;
       gid_t NO_GID = -1;
 
-      errno = 0;
-      euid = geteuid ();
-      if (euid == NO_UID && errno && !use_real
-          && !just_group && !just_group_list && !just_context)
-        error (EXIT_FAILURE, errno, _("cannot get effective UID"));
-
-      errno = 0;
-      ruid = getuid ();
-      if (ruid == NO_UID && errno && use_real
-          && !just_group && !just_group_list && !just_context)
-        error (EXIT_FAILURE, errno, _("cannot get real UID"));
-
-      errno = 0;
-      egid = getegid ();
-      if (egid == NO_GID && errno && !use_real && !just_user)
-        error (EXIT_FAILURE, errno, _("cannot get effective GID"));
-
-      errno = 0;
-      rgid = getgid ();
-      if (rgid == NO_GID && errno && use_real && !just_user)
-        error (EXIT_FAILURE, errno, _("cannot get real GID"));
+      if (just_user ? !use_real
+          : !just_group && !just_group_list && !just_context)
+        {
+          errno = 0;
+          euid = geteuid ();
+          if (euid == NO_UID && errno)
+            error (EXIT_FAILURE, errno, _("cannot get effective UID"));
+        }
+
+      if (just_user ? use_real
+          : !just_group && (just_group_list || !just_context))
+        {
+          errno = 0;
+          ruid = getuid ();
+          if (ruid == NO_UID && errno)
+            error (EXIT_FAILURE, errno, _("cannot get real UID"));
+        }
+
+      if (!just_user && (just_group || just_group_list || !just_context))
+        {
+          errno = 0;
+          egid = getegid ();
+          if (egid == NO_GID && errno)
+            error (EXIT_FAILURE, errno, _("cannot get effective GID"));
+
+          errno = 0;
+          rgid = getgid ();
+          if (rgid == NO_GID && errno)
+            error (EXIT_FAILURE, errno, _("cannot get real GID"));
+        }
     }
 
   if (just_user)
-- 
1.7.6.4