1 files changed, 13 insertions, 2 deletions

diff --git a/src/lib/libcrypto/bn/bn_div.c b/src/lib/libcrypto/bn/bn_div.c
index 8655eb118e..1e8e57626b 100644
--- a/src/lib/libcrypto/bn/bn_div.c
+++ b/src/lib/libcrypto/bn/bn_div.c
@@ -187,6 +187,17 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
         BN_ULONG d0,d1;
         int num_n,div_n;
 
+        /* Invalid zero-padding would have particularly bad consequences
+         * in the case of 'num', so don't just rely on bn_check_top() for this one
+         * (bn_check_top() works only for BN_DEBUG builds) */
+        if (num->top > 0 && num->d[num->top - 1] == 0)
+                {
+                BNerr(BN_F_BN_DIV,BN_R_NOT_INITIALIZED);
+                return 0;
+                }
+
+        bn_check_top(num);
+
         if ((BN_get_flags(num, BN_FLG_CONSTTIME) != 0) || (BN_get_flags(divisor, BN_FLG_CONSTTIME) != 0))
                 {
                 return BN_div_no_branch(dv, rm, num, divisor, ctx);
@@ -194,7 +205,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 
         bn_check_top(dv);
         bn_check_top(rm);
-        bn_check_top(num);
+        /* bn_check_top(num); */ /* 'num' has been checked already */
         bn_check_top(divisor);
 
         if (BN_is_zero(divisor))
@@ -419,7 +430,7 @@ static int BN_div_no_branch(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num,
 
         bn_check_top(dv);
         bn_check_top(rm);
-        bn_check_top(num);
+        /* bn_check_top(num); */ /* 'num' has been checked in BN_div() */
         bn_check_top(divisor);
 
         if (BN_is_zero(divisor))