Ensure Polyphemus-Mitigation and properly drop privileges

[slock.git] / slock.c

diff --git a/slock.c b/slock.c
index 62a9841..7127ebe 100644 (file)
--- a/slock.c
+++ b/slock.c
@@ -6,6 +6,7 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <grp.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdlib.h>
@@ -18,11 +19,6 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 
-#if HAVE_BSD_AUTH
-#include <login_cap.h>
-#include <bsd_auth.h>
-#endif
-
 #include "arg.h"
 #include "util.h"
 
@@ -88,14 +84,13 @@ dontkillme(void)
 }
 #endif
 
-#ifndef HAVE_BSD_AUTH
-/* only run as root */
 static const char *
 getpw(void)
 {
        const char *rval;
        struct passwd *pw;
 
+       /* Check if the current user has a password entry */
        errno = 0;
        if (!(pw = getpwuid(getuid()))) {
                if (errno)
@@ -109,25 +104,26 @@ getpw(void)
        if (rval[0] == 'x' && rval[1] == '\0') {
                struct spwd *sp;
                if (!(sp = getspnam(getenv("USER"))))
-                       die("slock: cannot retrieve shadow entry (make sure to suid or sgid slock)\n");
+                       die("slock: getspnam: cannot retrieve shadow entry (make sure to suid or sgid slock)\n");
                rval = sp->sp_pwdp;
        }
-#endif
+#else
+       if (rval[0] == '*' && rval[1] == '\0') {
+#ifdef __OpenBSD__
+               if (!(pw = getpwnam_shadow(getenv("USER"))))
+                       die("slock: getpwnam_shadow: cannot retrieve shadow entry (make sure to suid or sgid slock)\n");
+               rval = pw->pw_passwd;
+#else
+               die("slock: getpwuid: cannot retrieve shadow entry (make sure to suid or sgid slock)\n");
+#endif /* __OpenBSD__ */
+       }
+#endif /* HAVE_SHADOW_H */
 
-       /* drop privileges */
-       if (geteuid() == 0 &&
-           ((getegid() != pw->pw_gid && setgid(pw->pw_gid) < 0) || setuid(pw->pw_uid) < 0))
-               die("slock: cannot drop privileges\n");
        return rval;
 }
-#endif
 
 static void
-#ifdef HAVE_BSD_AUTH
-readpw(Display *dpy)
-#else
 readpw(Display *dpy, const char *pws)
-#endif
 {
        char buf[32], passwd[256], *encrypted;
        int num, screen, running, failure;
@@ -163,15 +159,11 @@ readpw(Display *dpy, const char *pws)
                        switch (ksym) {
                        case XK_Return:
                                passwd[len] = 0;
-#ifdef HAVE_BSD_AUTH
-                               running = !auth_userokay(getlogin(), NULL, "auth-slock", passwd);
-#else
                                errno = 0;
                                if (!(encrypted = crypt(passwd, pws)))
                                        fprintf(stderr, "slock: crypt: %s\n", strerror(errno));
                                else
                                        running = !!strcmp(encrypted, pws);
-#endif
                                if (running) {
                                        XBell(dpy, 100);
                                        failure = True;
@@ -320,9 +312,11 @@ usage(void)
 
 int
 main(int argc, char **argv) {
-#ifndef HAVE_BSD_AUTH
+       struct passwd *pwd;
+       struct group *grp;
+       uid_t duid;
+       gid_t dgid;
        const char *pws;
-#endif
        Display *dpy;
        int s, nlocks;
 
@@ -334,28 +328,37 @@ main(int argc, char **argv) {
                usage();
        } ARGEND
 
+       /* validate drop-user and -group */
+       errno = 0;
+       if (!(pwd = getpwnam(user)))
+               die("slock: getpwnam %s: %s\n", user, errno ?
+                   strerror(errno) : "user entry not found");
+       duid = pwd->pw_uid;
+       errno = 0;
+       if (!(grp = getgrnam(group)))
+               die("slock: getgrnam %s: %s\n", group, errno ?
+                   strerror(errno) : "group entry not found");
+       dgid = grp->gr_gid;
+
 #ifdef __linux__
        dontkillme();
 #endif
 
-       /* Check if the current user has a password entry */
-       errno = 0;
-       if (!getpwuid(getuid())) {
-               if (errno == 0)
-                       die("slock: no password entry for current user\n");
-               else
-                       die("slock: getpwuid: %s\n", strerror(errno));
-       }
-
-#ifndef HAVE_BSD_AUTH
        pws = getpw();
        if (strlen(pws) < 2)
                die("slock: failed to get user password hash.\n");
-#endif
 
        if (!(dpy = XOpenDisplay(NULL)))
                die("slock: cannot open display\n");
 
+       /* drop privileges */
+       if (setgroups(0, NULL) < 0)
+               die("slock: setgroups: %s\n", strerror(errno));
+       if (setgid(dgid) < 0)
+               die("slock: setgid: %s\n", strerror(errno));
+       if (setuid(duid) < 0)
+               die("slock: setuid: %s\n", strerror(errno));
+
        /* check for Xrandr support */
        rr = XRRQueryExtension(dpy, &rrevbase, &rrerrbase);
 
@@ -396,11 +399,7 @@ main(int argc, char **argv) {
        }
 
        /* everything is now blank. Wait for the correct password */
-#ifdef HAVE_BSD_AUTH
-       readpw(dpy);
-#else
        readpw(dpy, pws);
-#endif
 
        /* password ok, unlock everything and quit */
        cleanup(dpy);