| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CALrw=nH8zOXiyiCGkx1A533ijM=pyVebbhYCFpUyvP0bnjrXzA@mail.gmail.com>
Date: Tue, 20 Jan 2026 14:06:02 +0000
From: Ignat Korchagin <ignat@...udflare.com>
To: David Howells <dhowells@...hat.com>
Cc: Lukas Wunner <lukas@...ner.de>, Jarkko Sakkinen <jarkko@...nel.org>,
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 v12 02/10] pkcs7: Allow the signing algo to calculate the
digest itself
Hi David,
On Thu, Jan 15, 2026 at 9:51 PM David Howells <dhowells@...hat.com> wrote:
>
> The ML-DSA public key algorithm really wants to calculate the message
> digest itself, rather than having the digest precalculated and fed to it
> separately as RSA does[*]. The kernel's PKCS#7 parser, however, is
> designed around the latter approach.
>
> [*] ML-DSA does allow for an "external mu", but CMS doesn't yet have that
> standardised.
>
> Fix this by noting in the public_key_signature struct when the signing
> algorithm is going to want this and then, rather than doing the digest of
> the authenticatedAttributes ourselves and overwriting the sig->digest with
> that, replace sig->digest with a copy of the contents of the
> authenticatedAttributes section and adjust the digest length to match.
>
> This will then be fed to the public key algorithm as normal which can do
> what it wants with the data.
>
> 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/pkcs7_parser.c | 4 +--
> crypto/asymmetric_keys/pkcs7_verify.c | 48 ++++++++++++++++++---------
> include/crypto/public_key.h | 1 +
> 3 files changed, 36 insertions(+), 17 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
> index 423d13c47545..3cdbab3b9f50 100644
> --- a/crypto/asymmetric_keys/pkcs7_parser.c
> +++ b/crypto/asymmetric_keys/pkcs7_parser.c
> @@ -599,8 +599,8 @@ int pkcs7_sig_note_set_of_authattrs(void *context, size_t hdrlen,
> }
>
> /* We need to switch the 'CONT 0' to a 'SET OF' when we digest */
> - sinfo->authattrs = value - (hdrlen - 1);
> - sinfo->authattrs_len = vlen + (hdrlen - 1);
> + sinfo->authattrs = value - hdrlen;
> + sinfo->authattrs_len = vlen + hdrlen;
> return 0;
> }
>
> diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
> index 6d6475e3a9bf..0f9f515b784d 100644
> --- a/crypto/asymmetric_keys/pkcs7_verify.c
> +++ b/crypto/asymmetric_keys/pkcs7_verify.c
> @@ -70,8 +70,6 @@ static int pkcs7_digest(struct pkcs7_message *pkcs7,
> * digest we just calculated.
> */
> if (sinfo->authattrs) {
> - u8 tag;
> -
> if (!sinfo->msgdigest) {
> pr_warn("Sig %u: No messageDigest\n", sinfo->index);
> ret = -EKEYREJECTED;
> @@ -97,20 +95,40 @@ static int pkcs7_digest(struct pkcs7_message *pkcs7,
> * as the contents of the digest instead. Note that we need to
> * convert the attributes from a CONT.0 into a SET before we
> * hash it.
> + *
> + * However, for certain algorithms, such as ML-DSA, the digest
> + * is integrated into the signing algorithm. In such a case,
> + * we copy the authattrs, modifying the tag type, and set that
> + * as the digest.
> */
> - memset(sig->digest, 0, sig->digest_size);
> -
> - ret = crypto_shash_init(desc);
> - if (ret < 0)
> - goto error;
> - tag = ASN1_CONS_BIT | ASN1_SET;
> - ret = crypto_shash_update(desc, &tag, 1);
> - if (ret < 0)
> - goto error;
> - ret = crypto_shash_finup(desc, sinfo->authattrs,
> - sinfo->authattrs_len, sig->digest);
> - if (ret < 0)
> - goto error;
> + if (sig->algo_does_hash) {
> + kfree(sig->digest);
> +
> + ret = -ENOMEM;
> + sig->digest = kmalloc(umax(sinfo->authattrs_len, sig->digest_size),
> + GFP_KERNEL);
I'm still bothered by this "reallocation". You mentioned we need to do
some parsing for attributes, but it seems by the time this function is
called we have all the data to do something like
kmalloc(sig->algo_does_hash ? umax(sinfo->authattrs_len,
sig->digest_size) : sig->digest_size, GFP_KERNEL) during the initial
allocation. Or am I missing something?
> + if (!sig->digest)
> + goto error_no_desc;
> +
> + sig->digest_size = sinfo->authattrs_len;
> + memcpy(sig->digest, sinfo->authattrs, sinfo->authattrs_len);
> + ((u8 *)sig->digest)[0] = ASN1_CONS_BIT | ASN1_SET;
> + ret = 0;
> + } else {
> + u8 tag = ASN1_CONS_BIT | ASN1_SET;
> +
> + ret = crypto_shash_init(desc);
> + if (ret < 0)
> + goto error;
> + ret = crypto_shash_update(desc, &tag, 1);
> + if (ret < 0)
> + goto error;
> + ret = crypto_shash_finup(desc, sinfo->authattrs + 1,
> + sinfo->authattrs_len - 1,
> + sig->digest);
> + if (ret < 0)
> + goto error;
> + }
> pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
> }
>
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 81098e00c08f..e4ec8003a3a4 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -46,6 +46,7 @@ struct public_key_signature {
> u8 *digest;
> u32 s_size; /* Number of bytes in signature */
> u32 digest_size; /* Number of bytes in digest */
> + bool algo_does_hash; /* Public key algo does its own hashing */
nit: still do not like this name, but have no better alternatives so far
> const char *pkey_algo;
> const char *hash_algo;
> const char *encoding;
>
Ignat
Powered by blists - more mailing lists