[openssl/openssl] b8a5ad: Limit size of modulus for BN_mod_exp_mont_consttime()

[Tomáš Mráz]

  Branch: refs/heads/openssl-3.0
  Home:   https://github.com/openssl/openssl
  Commit: b8a5adf3ec46f1ce0fb80130f8b7c6e0dcb5bd41
      https://github.com/openssl/openssl/commit/b8a5adf3ec46f1ce0fb80130f8b7c6e0dcb5bd41
  Author: Tomas Mraz <tomas at openssl.org>
  Date:   2022-11-10 (Thu, 10 Nov 2022)

  Changed paths:
    M crypto/bn/bn_exp.c
    M test/exptest.c

  Log Message:
  -----------
  Limit size of modulus for BN_mod_exp_mont_consttime()

Otherwise the powerbufLen can overflow.

Issue reported by Jiayi Lin.

Reviewed-by: Matt Caswell <matt at openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit at gmail.com>
(Merged from https://github.com/openssl/openssl/pull/19632)

(cherry picked from commit 4378e3cd2a4d73a97a2349efaa143059d8ed05e8)