1 files changed, 30 insertions, 2 deletions

diff --git a/usbmuxd/main.c b/usbmuxd/main.c
index 3318ecd..ea332a4 100644
--- a/usbmuxd/main.c
+++ b/usbmuxd/main.c
@@ -34,6 +34,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #include <sys/un.h>
 #include <sys/stat.h>
 #include <getopt.h>
+#include <pwd.h>
 
 #include "log.h"
 #include "usb.h"
@@ -47,6 +48,7 @@ struct sigaction sa_old;
 
 static int verbose = 0;
 static int foreground = 0;
+static int drop_privileges = 0;
 
 int create_socket(void) {
         struct sockaddr_un bind_addr;
@@ -222,6 +224,7 @@ static void usage()
         printf("\t-h|--help                 Print this message.\n");
         printf("\t-v|--verbose              Be verbose (use twice or more to increase).\n");
         printf("\t-f|--foreground           Do not daemonize (implies a verbosity of 4).\n");
+        printf("\t-d|--drop-privileges      Drop privileges after startup.\n");
         printf("\n");
 }
 
@@ -231,12 +234,13 @@ static void parse_opts(int argc, char **argv)
                 {"help", 0, NULL, 'h'},
                 {"foreground", 0, NULL, 'f'},
                 {"verbose", 0, NULL, 'v'},
+                {"drop-privileges", 0, NULL, 'd'},
                 {NULL, 0, NULL, 0}
         };
         int c;
 
         while (1) {
-                c = getopt_long(argc, argv, "hfv", longopts, (int *) 0);
+                c = getopt_long(argc, argv, "hfvd", longopts, (int *) 0);
                 if (c == -1) {
                         break;
                 }
@@ -251,6 +255,9 @@ static void parse_opts(int argc, char **argv)
                 case 'v':
                         ++verbose;
                         break;
+                case 'd':
+                        drop_privileges = 1;
+                        break;
                 default:
                         usage();
                         exit(2);
@@ -304,7 +311,28 @@ int main(int argc, char *argv[])
                         exit(EXIT_FAILURE);
                 }
         }
-        
+
+        // drop elevated privileges
+        if (drop_privileges && (getuid() == 0 || geteuid() == 0)) {
+                struct passwd *pw = getpwnam("nobody");
+                if (pw) {
+                        setuid(pw->pw_uid);
+                } else {
+                        usbmuxd_log(LL_ERROR,
+                                   "ERROR: Dropping privileges failed, check if user 'nobody' exists! Will now terminate.");
+                        log_disable_syslog();
+                        exit(EXIT_FAILURE);
+                }
+
+                // security check
+                if (setuid(0) != -1) {
+                        usbmuxd_log(LL_ERROR, "ERROR: Failed to drop privileges properly!");
+                        log_disable_syslog();
+                        exit(EXIT_FAILURE);
+                }
+                usbmuxd_log(LL_NOTICE, "Successfully dropped privileges");
+        }
+
         res = main_loop(listenfd);
         if(res < 0)
                 usbmuxd_log(LL_FATAL, "main_loop failed");