Check for zero modulus in BN_MONT_CTX_set().

From OpenSSL 6a009812, prompted by a report by Guido Vranken

ok beck jsing

diff --git a/lib/libcrypto/bn/bn_mont.c b/lib/libcrypto/bn/bn_mont.c
index 45e312a..e01af70 100644 (file)
--- a/lib/libcrypto/bn/bn_mont.c
+++ b/lib/libcrypto/bn/bn_mont.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_mont.c,v 1.27 2021/12/04 16:05:46 tb Exp $ */
+/* $OpenBSD: bn_mont.c,v 1.28 2022/02/07 19:44:23 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -369,6 +369,9 @@ 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;