Re: [PATCH 2/2] KEYS: asymmetric: properly validate hash_algo and encoding

From: Eric Biggers <ebiggers@kernel.org>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: keyrings@vger.kernel.org, David Howells <dhowells@redhat.com>,
	linux-crypto@vger.kernel.org, linux-integrity@vger.kernel.org,
	Stefan Berger <stefanb@linux.ibm.com>,
	Gilad Ben-Yossef <gilad@benyossef.com>,
	Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
	Vitaly Chikunov <vt@altlinux.org>,
	Mimi Zohar <zohar@linux.ibm.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/2] KEYS: asymmetric: properly validate hash_algo and encoding
Date: Sun, 20 Feb 2022 18:21:36 -0800	[thread overview]
Message-ID: <YhL3MGQcwMujSxCr@sol.localdomain> (raw)
In-Reply-To: <YhLu8gZtdpphy5mB@kernel.org>

On Mon, Feb 21, 2022 at 02:46:26AM +0100, Jarkko Sakkinen wrote:
> On Mon, Jan 31, 2022 at 04:34:14PM -0800, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > It is insecure to allow arbitrary hash algorithms and signature
> > encodings to be used with arbitrary signature algorithms.  Notably,
> > ECDSA, ECRDSA, and SM2 all sign/verify raw hash values and don't
> > disambiguate between different hash algorithms like RSA PKCS#1 v1.5
> > padding does.  Therefore, they need to be restricted to certain sets of
> > hash algorithms (ideally just one, but in practice small sets are used).
> > Additionally, the encoding is an integral part of modern signature
> > algorithms, and is not supposed to vary.
> > 
> > Therefore, tighten the checks of hash_algo and encoding done by
> > software_key_determine_akcipher().
> > 
> > Also rearrange the parameters to software_key_determine_akcipher() to
> > put the public_key first, as this is the most important parameter and it
> > often determines everything else.
> > 
> > Fixes: 299f561a6693 ("x509: Add support for parsing x509 certs with ECDSA keys")
> > Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
> > Fixes: 0d7a78643f69 ("crypto: ecrdsa - add EC-RDSA (GOST 34.10) algorithm")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > ---
> >  crypto/asymmetric_keys/public_key.c | 111 +++++++++++++++++++---------
> >  1 file changed, 76 insertions(+), 35 deletions(-)
> > 
> > diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> > index aba7113d86c76..a603ee8afdb8d 100644
> > --- a/crypto/asymmetric_keys/public_key.c
> > +++ b/crypto/asymmetric_keys/public_key.c
> > @@ -60,39 +60,83 @@ static void public_key_destroy(void *payload0, void *payload3)
> >  }
> >  
> >  /*
> > - * Determine the crypto algorithm name.
> > + * Given a public_key, and an encoding and hash_algo to be used for signing
> > + * and/or verification with that key, determine the name of the corresponding
> > + * akcipher algorithm.  Also check that encoding and hash_algo are allowed.
> >   */
> > -static
> > -int software_key_determine_akcipher(const char *encoding,
> > -				    const char *hash_algo,
> > -				    const struct public_key *pkey,
> > -				    char alg_name[CRYPTO_MAX_ALG_NAME])
> > +static int
> > +software_key_determine_akcipher(const struct public_key *pkey,
> > +				const char *encoding, const char *hash_algo,
> > +				char alg_name[CRYPTO_MAX_ALG_NAME])
> 
> Why is changing parameter order necessary?
> 

It's mentioned in the commit message.  It's obviously not necessary but this way
makes much more sense IMO.

- Eric