1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
index 02125e6a9109..e1f8748ff25d 100644
--- a/drivers/isdn/isdnloop/isdnloop.c
+++ b/drivers/isdn/isdnloop/isdnloop.c
@@ -1070,6 +1070,12 @@ isdnloop_start(isdnloop_card *card, isdnloop_sdef *sdefp)
                 return -EBUSY;
         if (copy_from_user((char *) &sdef, (char *) sdefp, sizeof(sdef)))
                 return -EFAULT;
+
+        for (i = 0; i < 3; i++) {
+                if (!memchr(sdef.num[i], 0, sizeof(sdef.num[i])))
+                        return -EINVAL;
+        }
+
         spin_lock_irqsave(&card->isdnloop_lock, flags);
         switch (sdef.ptype) {
         case ISDN_PTYPE_EURO: