s390/pkey: Wipe sensitive data on failure

Wipe sensitive data from stack also if the copy_to_user() fails.

Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

drivers/s390/crypto/pkey_api.c

@@ -1377,7 +1377,7 @@ static long pkey_unlocked_ioctl(struct file *filp, unsigned int cmd,
 		if (rc)
 			break;
 		if (copy_to_user(ucs, &kcs, sizeof(kcs)))
-			return -EFAULT;
+			rc = -EFAULT;
 		memzero_explicit(&kcs, sizeof(kcs));
 		break;
 	}
@@ -1412,7 +1412,7 @@ static long pkey_unlocked_ioctl(struct file *filp, unsigned int cmd,
 		if (rc)
 			break;
 		if (copy_to_user(ucp, &kcp, sizeof(kcp)))
-			return -EFAULT;
+			rc = -EFAULT;
 		memzero_explicit(&kcp, sizeof(kcp));
 		break;
 	}