-/* setuid.c --- management of runtime priveleges.
+/* setuid.c --- management of runtime privileges.
* xscreensaver, Copyright (c) 1993-1998 Jamie Zawinski <jwz@jwz.org>
*
* Permission to use, copy, modify, distribute, and sell this software and its
char *s1 = strdup (uid_gid_string (uid, gid));
char *s2 = strdup (uid_gid_string (euid, egid));
- if (si->orig_uid && *si->orig_uid)
+ 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);
}
+static int
+set_ids_by_name (struct passwd *p, struct group *g, char **message_ret)
+{
+ int uid_errno = 0;
+ int gid_errno = 0;
+ uid_t uid = p->pw_uid;
+ gid_t gid = g->gr_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.
+ */
+ if (gid == (gid_t) -1) gid = (gid_t) -2;
+ if (uid == (uid_t) -1) uid = (uid_t) -2;
+
+ 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)
+ {
+ static char buf [1024];
+ sprintf (buf, "changed uid/gid to %s/%s (%ld/%ld).",
+ p->pw_name, (g ? g->gr_name : "???"),
+ (long) uid, (long) gid);
+ if (message_ret)
+ *message_ret = buf;
+ return 0;
+ }
+ else
+ {
+ char buf [1024];
+ if (gid_errno)
+ {
+ sprintf (buf, "%s: couldn't set gid to %s (%ld)",
+ blurb(),
+ (g ? g->gr_name : "???"),
+ (long) gid);
+ if (gid_errno == -1)
+ fprintf(stderr, "%s: unknown error\n", buf);
+ else
+ perror(buf);
+ }
+
+ if (uid_errno)
+ {
+ sprintf (buf, "%s: couldn't set uid to %s (%ld)",
+ blurb(),
+ (p ? p->pw_name : "???"),
+ (long) uid);
+ if (uid_errno == -1)
+ fprintf(stderr, "%s: unknown error\n", buf);
+ else
+ perror(buf);
+ }
+
+ return -1;
+ }
+}
+
+static int
+set_ids_by_number (uid_t uid, gid_t gid, char **message_ret)
+{
+ struct passwd *p;
+ struct group *g;
+
+ errno = 0;
+ p = getpwuid (uid);
+ if (!p)
+ {
+ char buf [1024];
+ sprintf (buf, "%s: error looking up name of user %d", blurb(),
+ (long) uid);
+ if (errno)
+ perror (buf);
+ else
+ fprintf (stderr, "%s: unknown error.\n", buf);
+ return -1;
+ }
+
+ errno = 0;
+ g = getgrgid (gid);
+ if (!g)
+ {
+ char buf [1024];
+ sprintf (buf, "%s: error looking up name of group %d", blurb(),
+ (long) gid);
+ if (errno)
+ perror (buf);
+ else
+ fprintf (stderr, "%s: unknown error.\n", buf);
+ return -1;
+ }
+
+ return set_ids_by_name (p, g, message_ret);
+}
+
+
/* 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
void
hack_uid (saver_info *si)
{
- si->orig_uid = strdup (uid_gid_string (geteuid(), getegid()));
- setgid (getgid ());
- setuid (getuid ());
+ /* 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);
+ }
- /* If we're being run as root (as from xdm) then switch the user id
- to something safe. */
- if (getuid () == 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.)
+ */
+ if (getuid() == (uid_t) 0)
{
- struct passwd *p = 0;
- struct group *g = 0;
- int uid_errno = 0;
- int gid_errno = 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.)
- */
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.
+ */
+ if (getuid() == (uid_t) 0)
+ {
+ struct passwd *p;
+
p = getpwnam ("nobody");
if (! p) p = getpwnam ("noaccess");
if (! p) p = getpwnam ("daemon");
saver_exit(si, 1, 0);
}
- g = getgrgid (p->pw_gid);
-
- /* 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.
- */
-
- if (p->pw_gid == -1) p->pw_gid = -2;
- if (p->pw_uid == -1) p->pw_uid = -2;
+ if (set_ids_by_number (p->pw_uid, p->pw_gid, &si->uid_message) != 0)
+ saver_exit (si, -1, 0);
+ }
- /* Change the gid to be a safe one, then change the uid to be a safe
- one (must do it in this order, because root privs vanish when uid
- is changed, and after that, gid can't be changed.)
- */
- if (setgid (p->pw_gid) != 0)
- gid_errno = errno ? errno : -1;
- if (setuid (p->pw_uid) != 0)
- uid_errno = errno ? errno : -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.
+ */
+ {
+ uid_t uid = getuid (); /* get it again */
+ struct passwd *p = getpwuid (uid); /* get it again */
- if (uid_errno == 0 && gid_errno == 0)
- {
- static char buf [1024];
- sprintf (buf, "changed uid/gid to %s/%s (%ld/%ld).",
- p->pw_name, (g ? g->gr_name : "???"),
- (long) p->pw_uid, (long) p->pw_gid);
- si->uid_message = buf;
- }
- else
- {
- char buf [1024];
- if (gid_errno)
- {
- sprintf (buf, "%s: couldn't set gid to %s (%ld)",
- blurb(),
- (g ? g->gr_name : "???"),
- (long) p->pw_gid);
- if (gid_errno == -1)
- fprintf(stderr, "%s: unknown error\n", buf);
- else
- perror(buf);
- }
-
- if (uid_errno)
- {
- sprintf (buf, "%s: couldn't set uid to %s (%ld)",
- blurb(),
- (p ? p->pw_name : "???"),
- (long) p->pw_uid);
- if (uid_errno == -1)
- fprintf(stderr, "%s: unknown error\n", buf);
- else
- perror(buf);
- }
- }
-
- if (uid_errno != 0)
- {
- /* We'd better exit rather than continue running as root.
- But if we switched uid but not gid, continue running,
- since that doesn't really matter. (Right?)
- */
- saver_exit (si, -1, 0);
- }
- }
-# ifndef NO_LOCKING
- else /* disable locking if already being run as "someone else" */
- {
- struct passwd *p = getpwuid (getuid ());
- if (!p ||
- !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 %s", p->pw_name);
- si->nolock_reason = buf;
- si->locking_disabled_p = True;
- }
- }
-# endif /* !NO_LOCKING */
+ 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 %s",
+ (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;
+ }
+ }
}
#else /* !NO_SETUID */
void hack_uid (saver_info *si) { }
-void hack_uid_warn (saver_info *si) { }
-void describe_uids (saver_info *si) { }
+void describe_uids (saver_info *si, FILE *out) { }
#endif /* NO_SETUID */
projects / xscreensaver / blobdiff