From 54681f6e5b689299bada4363adc2edc46a1d67b4 Mon Sep 17 00:00:00 2001
From: Richard Levitte <levitte@openssl.org>
Date: Mon, 27 Oct 2025 20:47:44 +0100
Subject: [PATCH] Set the 'tmp' flag BN_FLG_FIXED_TOP in
 bn_mod_exp_mont_fixed_top()

If not set, bn_check_top() trips when BN_DEBUG is defined

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28801)
---
 crypto/bn/bn_exp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 1dda2e017f1..ae6d9a21005 100644
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -766,6 +766,7 @@ int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
         for (i = 1; i < top; i++)
             tmp.d[i] = (~m->d[i]) & BN_MASK2;
         tmp.top = top;
+        tmp.flags |= BN_FLG_FIXED_TOP;
     } else
 #endif
     if (!bn_to_mont_fixed_top(&tmp, BN_value_one(), mont, ctx))
-- 
2.47.3