From: Matt Caswell <matt@openssl.org>
Date: Mon, 10 Aug 2015 11:00:29 +0000 (+0100)
Subject: Check for 0 modulus in BN_MONT_CTX_set
X-Git-Tag: OpenSSL_1_1_0-pre1~832
X-Git-Url: https://git.openssl.org/?p=openssl.git;a=commitdiff_plain;h=6a009812b2e249fed01488f6f19f9fbfd9ee74c4;ds=sidebyside

Check for 0 modulus in BN_MONT_CTX_set

The function BN_MONT_CTX_set was assuming that the modulus was non-zero
and therefore that |mod->top| > 0. In an error situation that may not be
the case and could cause a seg fault.

This is a follow on from CVE-2015-1794.

Reviewed-by: Richard Levitte <levitte@openssl.org>
---

diff --git a/crypto/bn/bn_mont.c b/crypto/bn/bn_mont.c
index 1580e978ce..d4d817a74f 100644
--- a/crypto/bn/bn_mont.c
+++ b/crypto/bn/bn_mont.c
@@ -351,6 +351,9 @@ int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
     int ret = 0;
     BIGNUM *Ri, *R;
 
+    if (BN_is_zero(mod))
+        return 0;
+
     BN_CTX_start(ctx);
     if ((Ri = BN_CTX_get(ctx)) == NULL)
         goto err;