added control-clear patch

config.def.h

@@ -10,3 +10,6 @@ static const char *colorname[NUMCOLS] = {
 
 /* treat a cleared input like a wrong password (color) */
 static const int failonclear = 1;
+
+/* allow control key to trigger fail on clear */
+static const int controlkeyclear = 0;

slock-git-20161012-control-clear.diff

@@ -0,0 +1,27 @@
+diff --git a/config.def.h b/config.def.h
+index 6fba2b6..933152b 100644
+--- a/config.def.h
++++ b/config.def.h
+@@ -10,3 +10,6 @@ static const char *colorname[NUMCOLS] = {
+ 
+ /* treat a cleared input like a wrong password */
+ static const int failonclear = 1;
++
++/* allow control key to trigger fail on clear */
++static const int controlkeyclear = 0;
+diff --git a/slock.c b/slock.c
+index 4d7f06f..15552ef 100644
+--- a/slock.c
++++ b/slock.c
+@@ -180,8 +180,9 @@ readpw(Display *dpy, struct xrandr *rr, struct lock **locks, int nscreens,
+ 					passwd[len--] = '\0';
+ 				break;
+ 			default:
+-				if (num && !iscntrl((int)buf[0]) &&
+-				    (len + num < sizeof(passwd))) {
++				if (controlkeyclear && iscntrl((int)buf[0]))
++					continue;
++				if (num && (len + num < sizeof(passwd))) {
+ 					memcpy(passwd + len, buf, num);
+ 					len += num;
+ 				}

slock.c

@@ -180,8 +180,9 @@ readpw(Display *dpy, struct xrandr *rr, struct lock **locks, int nscreens,
 					passwd[--len] = '\0';
 				break;
 			default:
-				if (num && !iscntrl((int)buf[0]) &&
+				if (controlkeyclear && iscntrl((int)buf[0]))
-				    (len + num < sizeof(passwd))) {
+					continue;
+				if (num && (len + num < sizeof(passwd))) {
 					memcpy(passwd + len, buf, num);
 					len += num;
 				}