/* setuid.c --- management of runtime privileges.
- * xscreensaver, Copyright (c) 1993-1998 Jamie Zawinski <jwz@jwz.org>
+ * 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
# include "config.h"
#endif
-#ifndef NO_SETUID /* whole file */
-
#include <X11/Xlib.h> /* not used for much... */
/* This file doesn't need the Xt headers, so stub these types out... */
#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)
+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, "%s/%s (%ld/%ld)",
+ sprintf (buf, "%.100s/%.100s (%ld/%ld)",
(p && p->pw_name ? p->pw_name : "???"),
(g && g->gr_name ? g->gr_name : "???"),
(long) uid, (long) gid);
}
+/* 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
-set_ids_by_name (struct passwd *p, struct group *g, char **message_ret)
+setgroups_needed_p (uid_t target_group)
+{
+ gid_t groups[1024];
+ int n = getgroups (sizeof(groups)-1, groups);
+ if (n < 0)
+ {
+ char buf [1024];
+ sprintf (buf, "%s: getgroups(%ld, ...)", blurb(), (long)sizeof(groups)-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;
- uid_t uid = p->pw_uid;
- gid_t gid = g->gr_gid;
+ int sgs_errno = 0;
+ struct passwd *p = getpwuid (uid);
+ struct group *g = getgrgid (gid);
if (message_ret)
*message_ret = 0;
-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.
+ 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;
if (setuid (uid) != 0)
uid_errno = errno ? errno : -1;
- if (uid_errno == 0 && gid_errno == 0)
+ if (uid_errno == 0 && gid_errno == 0 && sgs_errno == 0)
{
static char buf [1024];
- sprintf (buf, "changed uid/gid to %s/%s (%ld/%ld).",
- p->pw_name, (g ? g->gr_name : "???"),
+ 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;
else
{
char buf [1024];
+ gid_t groups[1024];
+ int n;
+
+ 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());
+ n = getgroups (sizeof(groups)-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 %s (%ld)",
+ sprintf (buf, "%s: couldn't set gid to %.100s (%ld)",
blurb(),
- (g ? g->gr_name : "???"),
+ (g && g->gr_name ? g->gr_name : "???"),
(long) gid);
if (gid_errno == -1)
fprintf(stderr, "%s: unknown error\n", buf);
else
- perror(buf);
+ {
+ errno = gid_errno;
+ perror(buf);
+ }
}
if (uid_errno)
{
- sprintf (buf, "%s: couldn't set uid to %s (%ld)",
+ sprintf (buf, "%s: couldn't set uid to %.100s (%ld)",
blurb(),
- (p ? p->pw_name : "???"),
+ (p && p->pw_name ? p->pw_name : "???"),
(long) uid);
if (uid_errno == -1)
fprintf(stderr, "%s: unknown error\n", buf);
else
- perror(buf);
+ {
+ errno = uid_errno;
+ 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
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)
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->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)
{
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 */
!strcmp (p->pw_name, "games"))
{
static char buf [1024];
- sprintf (buf, "running as %s",
+ sprintf (buf, "running as %.100s",
(p && p->pw_name && *p->pw_name
? p->pw_name : "<unknown>"));
si->nolock_reason = buf;
}
}
}
-
-#else /* !NO_SETUID */
-
-void hack_uid (saver_info *si) { }
-void describe_uids (saver_info *si, FILE *out) { }
-
-#endif /* NO_SETUID */
projects / xscreensaver / blobdiff