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

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Eric Biggers <ebiggers@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: Mon, 21 Feb 2022 21:16:47 +0100	[thread overview]
Message-ID: <YhPzL3v9b9L76I9w@iki.fi> (raw)
In-Reply-To: <YhL3MGQcwMujSxCr@sol.localdomain>

On Sun, Feb 20, 2022 at 06:21:36PM -0800, Eric Biggers wrote:
> 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.

Ah, so it is.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko