Don't close file descriptor 0

Closing a standard FD is a bad idea, as it will be reused by subsequent
system calls that create file descriptors.  Point FD 0 at /dev/null
instead.

Author: DemiMarie

daemon/qrexec-daemon.c

@@ -338,7 +338,6 @@ static void init(int xid)
         }
     }
 
-    close(0);
 
     if (chdir(socket_dir) < 0) {
         PERROR("chdir %s failed", socket_dir);
@@ -1572,6 +1571,18 @@ int main(int argc, char **argv)
     int i, opt;
     sigset_t selectmask;
 
+    {
+        int null_fd = open("/dev/null", O_RDONLY|O_NOCTTY);
+        if (null_fd < 0)
+            err(1, "open(%s)", "/dev/null");
+        if (null_fd > 0) {
+            if (dup2(null_fd, 0) != 0)
+                err(1, "dup2(%d, 0)", null_fd);
+            if (null_fd > 2 && close(null_fd) != 0)
+                err(1, "close(%d)", null_fd);
+        }
+    }
+
     setup_logging("qrexec-daemon");
 
     while ((opt=getopt_long(argc, argv, "hqp:D", longopts, NULL)) != -1) {