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Date: Mon, 20 Jul 2026 08:19:12 +0200
From: Lukas Wunner <lukas@wunner.de>
To: Jiangshan Yi <yijiangshan@kylinos.cn>
Cc: ignat@linux.win, herbert@gondor.apana.org.au, davem@davemloft.net,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
	13667453960@163.com
Subject: Re: [PATCH] crypto: rsassa-pkcs1 - Use constant-time digest
 comparison
Message-ID: <al294FVRcs8-ulcZ@wunner.de>
References: <20260720021322.122784-1-yijiangshan@kylinos.cn>
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In-Reply-To: <20260720021322.122784-1-yijiangshan@kylinos.cn>

On Mon, Jul 20, 2026 at 10:13:22AM +0800, Jiangshan Yi wrote:
> +++ b/crypto/rsassa-pkcs1.c
> @@ -291,7 +291,7 @@ static int rsassa_pkcs1_verify(struct crypto_sig *tfm,
>  	/* RFC 8017 sec 8.2.2 step 4 - comparison of digest with out_buf */
>  	if (dlen != dst_len - pos)
>  		return -EKEYREJECTED;
> -	if (memcmp(digest, out_buf + pos, dlen) != 0)
> +	if (crypto_memneq(digest, out_buf + pos, dlen))
>  		return -EKEYREJECTED;
>  
>  	return 0;

The exact same patch was previously submitted by someone else
and rejected:

https://lore.kernel.org/all/alEr_e-G0L2nxxv-@fudgebox/T/#u