linux-kernel - Re: [PATCH v14 2/5] x509: Separately calculate sha256 for blacklist

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Message-ID: <aXYp3Zb3rLudQBpE@kernel.org>
Date: Sun, 25 Jan 2026 16:34:05 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: Lukas Wunner <lukas@...ner.de>, Ignat Korchagin <ignat@...udflare.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Eric Biggers <ebiggers@...nel.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Daniel Gomez <da.gomez@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	"Jason A . Donenfeld" <Jason@...c4.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Stephan Mueller <smueller@...onox.de>, linux-crypto@...r.kernel.org,
	keyrings@...r.kernel.org, linux-modules@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 2/5] x509: Separately calculate sha256 for blacklist

On Wed, Jan 21, 2026 at 10:36:04PM +0000, David Howells wrote:
> Calculate the SHA256 hash for blacklisting purposes independently of the
> signature hash (which may be something other than SHA256).
> 
> This is necessary because when ML-DSA is used, no digest is calculated.
> 
> Note that this represents a change of behaviour in that the hash used for
> the blacklist check would previously have been whatever digest was used
> for, say, RSA-based signatures.  It may be that this is inadvisable.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Lukas Wunner <lukas@...ner.de>
> cc: Ignat Korchagin <ignat@...udflare.com>
> cc: Stephan Mueller <smueller@...onox.de>
> cc: Eric Biggers <ebiggers@...nel.org>
> cc: Herbert Xu <herbert@...dor.apana.org.au>
> cc: keyrings@...r.kernel.org
> cc: linux-crypto@...r.kernel.org
> ---
>  crypto/asymmetric_keys/x509_parser.h     |  2 ++
>  crypto/asymmetric_keys/x509_public_key.c | 23 +++++++++++++----------
>  2 files changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
> index 0688c222806b..b7aeebdddb36 100644
> --- a/crypto/asymmetric_keys/x509_parser.h
> +++ b/crypto/asymmetric_keys/x509_parser.h
> @@ -9,12 +9,14 @@
>  #include <linux/time.h>
>  #include <crypto/public_key.h>
>  #include <keys/asymmetric-type.h>
> +#include <crypto/sha2.h>
>  
>  struct x509_certificate {
>  	struct x509_certificate *next;
>  	struct x509_certificate *signer;	/* Certificate that signed this one */
>  	struct public_key *pub;			/* Public key details */
>  	struct public_key_signature *sig;	/* Signature parameters */
> +	u8		sha256[SHA256_DIGEST_SIZE]; /* Hash for blacklist purposes */
>  	char		*issuer;		/* Name of certificate issuer */
>  	char		*subject;		/* Name of certificate subject */
>  	struct asymmetric_key_id *id;		/* Issuer + Serial number */
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index 12e3341e806b..6d002e3b20c5 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -31,6 +31,19 @@ int x509_get_sig_params(struct x509_certificate *cert)
>  
>  	pr_devel("==>%s()\n", __func__);
>  
> +	/* Calculate a SHA256 hash of the TBS and check it against the
> +	 * blacklist.
> +	 */
> +	sha256(cert->tbs, cert->tbs_size, cert->sha256);
> +	ret = is_hash_blacklisted(cert->sha256, sizeof(cert->sha256),
> +				  BLACKLIST_HASH_X509_TBS);
> +	if (ret == -EKEYREJECTED) {
> +		pr_err("Cert %*phN is blacklisted\n",
> +		       (int)sizeof(cert->sha256), cert->sha256);
> +		cert->blacklisted = true;
> +		ret = 0;
> +	}
> +
>  	sig->s = kmemdup(cert->raw_sig, cert->raw_sig_size, GFP_KERNEL);
>  	if (!sig->s)
>  		return -ENOMEM;
> @@ -65,19 +78,9 @@ int x509_get_sig_params(struct x509_certificate *cert)
>  
>  	ret = crypto_shash_digest(desc, cert->tbs, cert->tbs_size,
>  				  sig->digest);
> -

nit: spurious diff unrelated to change

>  	if (ret < 0)
>  		goto error_2;
>  
> -	ret = is_hash_blacklisted(sig->digest, sig->digest_size,
> -				  BLACKLIST_HASH_X509_TBS);
> -	if (ret == -EKEYREJECTED) {
> -		pr_err("Cert %*phN is blacklisted\n",
> -		       sig->digest_size, sig->digest);
> -		cert->blacklisted = true;
> -		ret = 0;
> -	}
> -
>  error_2:
>  	kfree(desc);
>  error:
> 

I hold on for commentary (nit was is not reason to not give
reviewed-by) tho it looks to me acceptable.

BR, Jarkko