diff options
Diffstat (limited to 'driver/setuid.c')
-rw-r--r-- | driver/setuid.c | 361 |
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; + } + } +} |