1 files changed, 69 insertions, 160 deletions

diff --git a/driver/setuid.c b/driver/setuid.c
index 3ac78e4..164576f 100644
--- a/driver/setuid.c
+++ b/driver/setuid.c
@@ -1,5 +1,5 @@
 /* setuid.c --- management of runtime privileges.
- * xscreensaver, Copyright (c) 1993-1998, 2005 Jamie Zawinski <jwz@jwz.org>
+ * xscreensaver, Copyright © 1993-2021 Jamie Zawinski <jwz@jwz.org>
  *
  * Permission to use, copy, modify, distribute, and sell this software and its
  * documentation for any purpose is hereby granted without fee, provided that
@@ -14,24 +14,20 @@
 # include "config.h"
 #endif
 
-#include <X11/Xlib.h>		/* not used for much... */
-
-/* This file doesn't need the Xt headers, so stub these types out... */
-#undef XtPointer
-#define XtAppContext void*
-#define XrmDatabase  void*
-#define XtIntervalId void*
-#define XtPointer    void*
-#define Widget       void*
-
-#include "xscreensaver.h"
-
-#ifndef EPERM
-#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
 #endif
 
+#include <string.h>
 #include <pwd.h>		/* for getpwnam() and struct passwd */
 #include <grp.h>		/* for getgrgid() and struct group */
+#include <errno.h>
+
+#include "blurb.h"
+#include "auth.h"
+
 
 static const char *
 uid_gid_string (uid_t uid, gid_t gid)
@@ -49,31 +45,6 @@ uid_gid_string (uid_t uid, gid_t gid)
 }
 
 
-void
-describe_uids (saver_info *si, FILE *out)
-{
-  uid_t uid = getuid();
-  gid_t gid = getgid();
-  uid_t euid = geteuid();
-  gid_t egid = getegid();
-  char *s1 = strdup (uid_gid_string (uid, gid));
-  char *s2 = strdup (uid_gid_string (euid, egid));
-
-  if (si->orig_uid && *si->orig_uid &&
-      (!!strcmp (si->orig_uid, s1) ||
-       !!strcmp (si->orig_uid, s2)))
-    fprintf (out, "%s: initial effective uid/gid was %s\n", blurb(),
-	     si->orig_uid);
-
-  fprintf (out, "%s: running as %s", blurb(), s1);
-  if (uid != euid || gid != egid)
-    fprintf (out, "; effectively %s", s2);
-  fprintf(out, "\n");
-  free(s1);
-  free(s2);
-}
-
-
 /* Returns true if we need to call setgroups().
 
    Without calling setgroups(), the process will retain any supplementary
@@ -113,7 +84,7 @@ setgroups_needed_p (uid_t target_group)
 
 
 static int
-set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
+set_ids_by_number (uid_t uid, gid_t gid)
 {
   int uid_errno = 0;
   int gid_errno = 0;
@@ -121,9 +92,6 @@ set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
   struct passwd *p = getpwuid (uid);
   struct group  *g = getgrgid (gid);
 
-  if (message_ret)
-    *message_ret = 0;
-
   /* Rumor has it that some implementations of of setuid() do nothing
      when called with -1; therefore, if the "nobody" user has a uid of
      -1, then that would be Really Bad.  Rumor further has it that such
@@ -150,13 +118,12 @@ set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
 
   if (uid_errno == 0 && gid_errno == 0 && sgs_errno == 0)
     {
-      static char buf [1024];
-      sprintf (buf, "changed uid/gid to %.100s/%.100s (%ld/%ld).",
-	       (p && p->pw_name ? p->pw_name : "???"),
-               (g && g->gr_name ? g->gr_name : "???"),
-	       (long) uid, (long) gid);
-      if (message_ret)
-	*message_ret = buf;
+      if (verbose_p)
+        fprintf (stderr, "%s: changed uid/gid to %.100s/%.100s (%ld/%ld)\n",
+                 blurb(),
+                 (p && p->pw_name ? p->pw_name : "???"),
+                 (g && g->gr_name ? g->gr_name : "???"),
+                 (long) uid, (long) gid);
       return 0;
     }
   else
@@ -176,7 +143,7 @@ set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
 	  else
             {
               errno = sgs_errno;
-              perror(buf);
+              perror (buf);
             }
 
 	  fprintf (stderr, "%s: effective group list: ", blurb());
@@ -206,11 +173,11 @@ set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
 		   (g && g->gr_name ? g->gr_name : "???"),
 		   (long) gid);
 	  if (gid_errno == -1)
-	    fprintf(stderr, "%s: unknown error\n", buf);
+	    fprintf (stderr, "%s: unknown error\n", buf);
 	  else
             {
               errno = gid_errno;
-              perror(buf);
+              perror (buf);
             }
 	}
 
@@ -241,121 +208,63 @@ set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
    lock-mode.)
 
      *** WARNING: DO NOT DISABLE ANY OF THE FOLLOWING CODE!
-         If you do so, you will open a security hole.  See the sections
-         of the xscreensaver manual titled "LOCKING AND ROOT LOGINS", 
-         and "USING XDM".
+         If you do so, you will open a security hole.
+         Do not log in to an X11 desktop as root.
+         Log in as a normal users and 'sudo' as needed.
  */
 void
-hack_uid (saver_info *si)
+disavow_privileges (void)
 {
+  uid_t euid = geteuid();
+  gid_t egid = getegid();
+  uid_t uid = getuid();
+  gid_t gid = getgid();
+  struct passwd *p;
 
-  /* Discard privileges, and set the effective user/group ids to the
-     real user/group ids.  That is, give up our "chmod +s" rights.
-   */
-  {
-    uid_t euid = geteuid();
-    gid_t egid = getegid();
-    uid_t uid = getuid();
-    gid_t gid = getgid();
-
-    si->orig_uid = strdup (uid_gid_string (euid, egid));
-
-    if (uid != euid || gid != egid)
-      if (set_ids_by_number (uid, gid, &si->uid_message) != 0)
-	saver_exit (si, 1, 0);
-  }
-
-
-  /* Locking can't work when running as root, because we have no way of
-     knowing what the user id of the logged in user is (so we don't know
-     whose password to prompt for.)
-
-     *** WARNING: DO NOT DISABLE THIS CODE!
-         If you do so, you will open a security hole.  See the sections
-         of the xscreensaver manual titled "LOCKING AND ROOT LOGINS",
-         and "USING XDM".
-   */
-  if (getuid() == (uid_t) 0)
+  if (uid != euid || gid != egid)
     {
-      si->locking_disabled_p = True;
-      si->nolock_reason = "running as root";
+      if (verbose_p)
+        fprintf (stderr, "%s: initial effective uid/gid was %s\n", blurb(),
+                 uid_gid_string (euid, egid));
+      if (set_ids_by_number (uid, gid) != 0)
+        exit (1);  /* already printed error */
     }
 
-
-  /* If we're running as root, switch to a safer user.  This is above and
-     beyond the fact that we've disabling locking, above -- the theory is
-     that running graphics demos as root is just always a stupid thing
-     to do, since they have probably never been security reviewed and are
-     more likely to be buggy than just about any other kind of program.
-     (And that assumes non-malicious code.  There are also attacks here.)
-
-     *** WARNING: DO NOT DISABLE THIS CODE!
-         If you do so, you will open a security hole.  See the sections
-         of the xscreensaver manual titled "LOCKING AND ROOT LOGINS", 
-         and "USING XDM".
+  /* If we're still running as root, or if the user we are running at seems
+     to be in any way hinky, exit and do not allow password authentication
+     to continue.
    */
-  if (getuid() == (uid_t) 0)
-    {
-      struct passwd *p;
-
-      p = getpwnam ("nobody");
-      if (! p) p = getpwnam ("noaccess");
-      if (! p) p = getpwnam ("daemon");
-      if (! p)
-	{
-	  fprintf (stderr,
-		   "%s: running as root, and couldn't find a safer uid.\n",
-		   blurb());
-	  saver_exit(si, 1, 0);
-	}
+  uid = getuid ();	/* get it again */
+  p = getpwuid (uid);
 
-      if (set_ids_by_number (p->pw_uid, p->pw_gid, &si->uid_message) != 0)
-	saver_exit (si, -1, 0);
+  if (!p ||
+      uid == (uid_t)  0 ||
+      uid == (uid_t) -1 ||
+      uid == (uid_t) -2 ||
+      p->pw_uid == (uid_t)  0 ||
+      p->pw_uid == (uid_t) -1 ||
+      p->pw_uid == (uid_t) -2 ||
+      !p->pw_name ||
+      !*p->pw_name ||
+      !strcmp (p->pw_name, "root") ||
+      !strcmp (p->pw_name, "nobody") ||
+      !strcmp (p->pw_name, "noaccess") ||
+      !strcmp (p->pw_name, "operator") ||
+      !strcmp (p->pw_name, "daemon") ||
+      !strcmp (p->pw_name, "bin") ||
+      !strcmp (p->pw_name, "adm") ||
+      !strcmp (p->pw_name, "sys") ||
+      !strcmp (p->pw_name, "games"))
+    {
+      fprintf (stderr,
+               "%s: running as user \"%s\" -- authentication disallowed\n",
+               blurb(),
+               (p && p->pw_name && *p->pw_name
+                ? p->pw_name
+                : "<unknown>"));
+      exit (1);
     }
 
-
-  /* If there's anything even remotely funny looking about the passwd struct,
-     or if we're running as some other user from the list below (a
-     non-comprehensive selection of users known to be privileged in some way,
-     and not normal end-users) then disable locking.  If it was possible,
-     switching to "nobody" would be the thing to do, but only root itself has
-     the privs to do that.
-
-     *** WARNING: DO NOT DISABLE THIS CODE!
-         If you do so, you will open a security hole.  See the sections
-         of the xscreensaver manual titled "LOCKING AND ROOT LOGINS",
-         and "USING XDM".
-   */
-  {
-    uid_t uid = getuid ();		/* get it again */
-    struct passwd *p = getpwuid (uid);	/* get it again */
-
-    if (!p ||
-	uid == (uid_t)  0 ||
-	uid == (uid_t) -1 ||
-	uid == (uid_t) -2 ||
-	p->pw_uid == (uid_t)  0 ||
-	p->pw_uid == (uid_t) -1 ||
-	p->pw_uid == (uid_t) -2 ||
-	!p->pw_name ||
-	!*p->pw_name ||
-	!strcmp (p->pw_name, "root") ||
-	!strcmp (p->pw_name, "nobody") ||
-	!strcmp (p->pw_name, "noaccess") ||
-	!strcmp (p->pw_name, "operator") ||
-	!strcmp (p->pw_name, "daemon") ||
-	!strcmp (p->pw_name, "bin") ||
-	!strcmp (p->pw_name, "adm") ||
-	!strcmp (p->pw_name, "sys") ||
-	!strcmp (p->pw_name, "games"))
-      {
-	static char buf [1024];
-	sprintf (buf, "running as %.100s",
-		 (p && p->pw_name && *p->pw_name
-		  ? p->pw_name : "<unknown>"));
-	si->nolock_reason = buf;
-	si->locking_disabled_p = True;
-	si->dangerous_uid_p = True;
-      }
-  }
+  if (verbose_p)
+    fprintf (stderr, "%s: running as user \"%s\"\n", blurb(), p->pw_name);
 }