Check for invalid divisors in BN_div.

Invalid zero-padding in the divisor could cause a division by 0.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit a43bcd9e96c5180e5c6c82164ece643c0097485e)

diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c
index 06d87d0aaf145d7e05961ab3c14d2ecadecad99c..1b5c29c7ac07cc84d33cff1d39231ae0a6b1f809 100644 (file)
--- a/crypto/bn/bn_div.c
+++ b/crypto/bn/bn_div.c
@@ -190,15 +190,17 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
        int no_branch=0;
 
        /* 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
+        * so don't just rely on bn_check_top() here
         * (bn_check_top() works only for BN_DEBUG builds) */
-       if (num->top > 0 && num->d[num->top - 1] == 0)
+       if ((num->top > 0 && num->d[num->top - 1] == 0) ||
+               (divisor->top > 0 && divisor->d[divisor->top - 1] == 0))
                {
                BNerr(BN_F_BN_DIV,BN_R_NOT_INITIALIZED);
                return 0;
                }
 
        bn_check_top(num);
+       bn_check_top(divisor);
 
        if ((BN_get_flags(num, BN_FLG_CONSTTIME) != 0) || (BN_get_flags(divisor, BN_FLG_CONSTTIME) != 0))
                {
@@ -208,7 +210,7 @@ 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); */ /* 'num' has been checked already */
-       bn_check_top(divisor);
+       /* bn_check_top(divisor); */ /* 'divisor' has been checked already */
 
        if (BN_is_zero(divisor))
                {