From 6aea58d0eafb93e85312960b4eda01f344e29e12 Mon Sep 17 00:00:00 2001
From: Adam Langley <agl@chromium.org>
Date: Fri, 20 Jun 2014 12:00:00 -0700
Subject: [PATCH] Check for invalid divisors in BN_div.

---
 crypto/bn/div.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/crypto/bn/div.c b/crypto/bn/div.c
index 5f92e9e3..5fc43dca 100644
--- a/crypto/bn/div.c
+++ b/crypto/bn/div.c
@@ -122,8 +122,9 @@ 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'. */
-  if (num->top > 0 && num->d[num->top - 1] == 0) {
+   * so don't just rely on bn_check_top() here */
+  if ((num->top > 0 && num->d[num->top - 1] == 0) ||
+      (divisor->top > 0 && divisor->d[divisor->top - 1] == 0)) {
     OPENSSL_PUT_ERROR(BN, BN_div, BN_R_NOT_INITIALIZED);
     return 0;
   }