Add a comment that explains what the check is doing and why len >= 1.

Prompted by a remark by jsing

1 files changed, 2 insertions, 1 deletions

diff --git a/src/lib/libcrypto/evp/evp_key.c b/src/lib/libcrypto/evp/evp_key.c
index debd1b7561..91d0fc0de9 100644
--- a/src/lib/libcrypto/evp/evp_key.c
+++ b/src/lib/libcrypto/evp/evp_key.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: evp_key.c,v 1.25 2018/08/14 17:51:36 tb Exp $ */
+/* $OpenBSD: evp_key.c,v 1.26 2018/08/14 17:59:26 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -103,6 +103,7 @@ EVP_read_pw_string_min(char *buf, int min, int len, const char *prompt,
 
         if (len > BUFSIZ)
                 len = BUFSIZ;
+        /* Ensure that 0 <= min <= len - 1. In particular, 1 <= len. */
         if (min < 0 || len - 1 < min)
                 return -1;
         if ((prompt == NULL) && (prompt_string[0] != '\0'))