1 files changed, 12 insertions, 6 deletions

diff --git a/src/lib/libcrypto/bn/bn_sqr.c b/src/lib/libcrypto/bn/bn_sqr.c
index c1d0cca438..270d0cd348 100644
--- a/src/lib/libcrypto/bn/bn_sqr.c
+++ b/src/lib/libcrypto/bn/bn_sqr.c
@@ -77,16 +77,16 @@ int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
         if (al <= 0)
                 {
                 r->top=0;
-                return(1);
+                return 1;
                 }
 
         BN_CTX_start(ctx);
         rr=(a != r) ? r : BN_CTX_get(ctx);
         tmp=BN_CTX_get(ctx);
-        if (tmp == NULL) goto err;
+        if (!rr || !tmp) goto err;
 
-        max=(al+al);
-        if (bn_wexpand(rr,max+1) == NULL) goto err;
+        max = 2 * al; /* Non-zero (from above) */
+        if (bn_wexpand(rr,max) == NULL) goto err;
 
         if (al == 4)
                 {
@@ -138,12 +138,18 @@ int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
 #endif
                 }
 
-        rr->top=max;
         rr->neg=0;
-        if ((max > 0) && (rr->d[max-1] == 0)) rr->top--;
+        /* If the most-significant half of the top word of 'a' is zero, then
+         * the square of 'a' will max-1 words. */
+        if(a->d[al - 1] == (a->d[al - 1] & BN_MASK2l))
+                rr->top = max - 1;
+        else
+                rr->top = max;
         if (rr != r) BN_copy(r,rr);
         ret = 1;
  err:
+        bn_check_top(rr);
+        bn_check_top(tmp);
         BN_CTX_end(ctx);
         return(ret);
         }