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-rw-r--r--driver/setuid.c361
1 files changed, 361 insertions, 0 deletions
diff --git a/driver/setuid.c b/driver/setuid.c
new file mode 100644
index 0000000..3ac78e4
--- /dev/null
+++ b/driver/setuid.c
@@ -0,0 +1,361 @@
+/* setuid.c --- management of runtime privileges.
+ * xscreensaver, Copyright (c) 1993-1998, 2005 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
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation. No representations are made about the suitability of this
+ * software for any purpose. It is provided "as is" without express or
+ * implied warranty.
+ */
+
+#ifdef HAVE_CONFIG_H
+# 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>
+#endif
+
+#include <pwd.h> /* for getpwnam() and struct passwd */
+#include <grp.h> /* for getgrgid() and struct group */
+
+static const char *
+uid_gid_string (uid_t uid, gid_t gid)
+{
+ static char buf[255];
+ struct passwd *p = 0;
+ struct group *g = 0;
+ p = getpwuid (uid);
+ g = getgrgid (gid);
+ sprintf (buf, "%.100s/%.100s (%ld/%ld)",
+ (p && p->pw_name ? p->pw_name : "???"),
+ (g && g->gr_name ? g->gr_name : "???"),
+ (long) uid, (long) gid);
+ return buf;
+}
+
+
+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
+ gids associated with the uid, e.g.:
+
+ % groups root
+ root : root bin daemon sys adm disk wheel
+
+ However, setgroups() can only be called by root, and returns EPERM
+ for other users even if the call would be a no-op (e.g., setting the
+ group list to the current list.) So, to avoid that spurious error,
+ before calling setgroups() we first check whether the current list
+ of groups contains only one element, our target group. If so, we
+ don't need to call setgroups().
+ */
+static int
+setgroups_needed_p (uid_t target_group)
+{
+ gid_t groups[1024];
+ int n, size;
+ size = sizeof(groups) / sizeof(gid_t);
+ n = getgroups (size - 1, groups);
+ if (n < 0)
+ {
+ char buf [1024];
+ sprintf (buf, "%s: getgroups(%ld, ...)", blurb(), (long int)(size - 1));
+ perror (buf);
+ return 1;
+ }
+ else if (n == 0) /* an empty list means only egid is in effect. */
+ return 0;
+ else if (n == 1 && groups[0] == target_group) /* one element, the target */
+ return 0;
+ else /* more than one, or the wrong one. */
+ return 1;
+}
+
+
+static int
+set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
+{
+ int uid_errno = 0;
+ int gid_errno = 0;
+ int sgs_errno = 0;
+ 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
+ systems really ought to be using -2 for "nobody", since that works.
+ So, if we get a uid (or gid, for good measure) of -1, switch to -2
+ instead. Note that this must be done after we've looked up the
+ user/group names with getpwuid(-1) and/or getgrgid(-1).
+ */
+ if (gid == (gid_t) -1) gid = (gid_t) -2;
+ if (uid == (uid_t) -1) uid = (uid_t) -2;
+
+ errno = 0;
+ if (setgroups_needed_p (gid) &&
+ setgroups (1, &gid) < 0)
+ sgs_errno = errno ? errno : -1;
+
+ errno = 0;
+ if (setgid (gid) != 0)
+ gid_errno = errno ? errno : -1;
+
+ errno = 0;
+ if (setuid (uid) != 0)
+ uid_errno = errno ? errno : -1;
+
+ 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;
+ return 0;
+ }
+ else
+ {
+ char buf [1024];
+ gid_t groups[1024];
+ int n, size;
+
+ if (sgs_errno)
+ {
+ sprintf (buf, "%s: couldn't setgroups to %.100s (%ld)",
+ blurb(),
+ (g && g->gr_name ? g->gr_name : "???"),
+ (long) gid);
+ if (sgs_errno == -1)
+ fprintf(stderr, "%s: unknown error\n", buf);
+ else
+ {
+ errno = sgs_errno;
+ perror(buf);
+ }
+
+ fprintf (stderr, "%s: effective group list: ", blurb());
+ size = sizeof(groups) / sizeof(gid_t);
+ n = getgroups (size - 1, groups);
+ if (n < 0)
+ fprintf (stderr, "unknown!\n");
+ else
+ {
+ int i;
+ fprintf (stderr, "[");
+ for (i = 0; i < n; i++)
+ {
+ g = getgrgid (groups[i]);
+ if (i > 0) fprintf (stderr, ", ");
+ if (g && g->gr_name) fprintf (stderr, "%s", g->gr_name);
+ else fprintf (stderr, "%ld", (long) groups[i]);
+ }
+ fprintf (stderr, "]\n");
+ }
+ }
+
+ if (gid_errno)
+ {
+ sprintf (buf, "%s: couldn't set gid to %.100s (%ld)",
+ blurb(),
+ (g && g->gr_name ? g->gr_name : "???"),
+ (long) gid);
+ if (gid_errno == -1)
+ fprintf(stderr, "%s: unknown error\n", buf);
+ else
+ {
+ errno = gid_errno;
+ perror(buf);
+ }
+ }
+
+ if (uid_errno)
+ {
+ sprintf (buf, "%s: couldn't set uid to %.100s (%ld)",
+ blurb(),
+ (p && p->pw_name ? p->pw_name : "???"),
+ (long) uid);
+ if (uid_errno == -1)
+ fprintf(stderr, "%s: unknown error\n", buf);
+ else
+ {
+ errno = uid_errno;
+ perror(buf);
+ }
+ }
+
+ return -1;
+ }
+}
+
+
+/* If we've been run as setuid or setgid to someone else (most likely root)
+ turn off the extra permissions so that random user-specified programs
+ don't get special privileges. (On some systems it is necessary to install
+ this program as setuid root in order to read the passwd file to implement
+ 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".
+ */
+void
+hack_uid (saver_info *si)
+{
+
+ /* 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)
+ {
+ si->locking_disabled_p = True;
+ si->nolock_reason = "running as root";
+ }
+
+
+ /* 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 (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);
+ }
+
+ if (set_ids_by_number (p->pw_uid, p->pw_gid, &si->uid_message) != 0)
+ saver_exit (si, -1, 0);
+ }
+
+
+ /* 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;
+ }
+ }
+}
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