Ensure Polyphemus-Mitigation and properly drop privileges

[slock.git] / slock.c

diff --git a/slock.c b/slock.c
index da4b0995dc34be6e07940b2f68eee9a3566b0a03..7127ebe0827460a4b6d9d71ea722b83e21a4ee7b 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>
@@ -83,7 +84,6 @@ dontkillme(void)
 }
 #endif
 
-/* only run as root */
 static const char *
 getpw(void)
 {
@@ -119,10 +119,6 @@ getpw(void)
        }
 #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;
 }
 
@@ -316,6 +312,10 @@ usage(void)
 
 int
 main(int argc, char **argv) {
+       struct passwd *pwd;
+       struct group *grp;
+       uid_t duid;
+       gid_t dgid;
        const char *pws;
        Display *dpy;
        int s, nlocks;
@@ -328,6 +328,18 @@ 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
@@ -339,6 +351,14 @@ main(int argc, char **argv) {
        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);