Add conditional around bn_mul_words() call.

At least one of our bn_mul_words() assembly implementation fails to handle
n = 0 correctly... *sigh*

1 files changed, 4 insertions, 2 deletions

diff --git a/src/lib/libcrypto/bn/bn_sqr.c b/src/lib/libcrypto/bn/bn_sqr.c
index 56664e2e36..5ea1bd45b9 100644
--- a/src/lib/libcrypto/bn/bn_sqr.c
+++ b/src/lib/libcrypto/bn/bn_sqr.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_sqr.c,v 1.33 2023/06/24 16:19:52 jsing Exp $ */
+/* $OpenBSD: bn_sqr.c,v 1.34 2023/06/24 17:06:54 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -214,7 +214,9 @@ bn_sqr_normal(BN_ULONG *r, int r_len, const BN_ULONG *a, int a_len,
 
         /* Compute initial product - r[n:1] = a[n:1] * a[0] */
         n = a_len - 1;
-        rp[n] = bn_mul_words(rp, ap, n, w);
+        if (n > 0) {
+                rp[n] = bn_mul_words(rp, ap, n, w);
+        }
         rp += 2;
         n--;