From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 437BC13049E for ; Tue, 23 Jul 2024 01:36:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721698564; cv=none; b=Hm0lfCIJklvCgDHxBtKcJyR9pRGaUDn0SlIkHUwm6GKL4G9IeBxjtqJPIQEwaS/nLIhgWCK/e2z88hv6/oHr1Pn2Y8skQs+wn6ZOqjBgzq2Ute8isquyqmeNuWLh5QSzuUdnNDmWysF1UvfSfDcUyRByUngI1/BX9QvH6ZrcVlc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721698564; c=relaxed/simple; bh=EHmJAS5gLxznHMyE9QZw/Fdm6OSkClD/yGhdKpoAato=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JDwOeD5wzvfDHwH6gi0MVessiQgskz2J3T4vzHn724ZCJMXlcgtTNOxYUUfEjvQKAaEia6t6d20P2MWHY9X/q+dlVs7+hHYz1CrPBIHxAblmudOiXYC0+gINOrowOJcIhbMXUfCj/OYmuazEYLHNk6S5YU8uA6Z/3pq5YzJsB7g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=upCPwLzB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="upCPwLzB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C0647C116B1; Tue, 23 Jul 2024 01:36:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721698563; bh=EHmJAS5gLxznHMyE9QZw/Fdm6OSkClD/yGhdKpoAato=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=upCPwLzBixeAEMPKelny1iv8LwUuCLd33wxWtLrbN/gJzjRLIvBFLY2tTuk3GYHN/ f+/8LILzQzBQ8pZ5CksYqIzCsREox+j3X31KI95uhJ5+7Sz1LhDeaZjpEp68ZZDnPX 9cYH2Fv1bi12m9eJEOgfVRpPBtsjPZEuIC9DsW9DBwuPvUS/rbcvgLiCrQleD3boHR lL1CB3Qu6X6jGCzjf5vdC0GJrkkSMBJpeWTD0E7MVKk11gFhuzGw78OBrq/T0Mouz5 kitKQM5X+0JNFV/lQbCmtYdK2UUOI8CfY1OAdwrKypNMmyUtbzM1ubwv6G/X9xb3Bf K+SyN9a5ms+ug== Date: Tue, 23 Jul 2024 01:36:02 +0000 From: Eric Biggers To: Hannes Reinecke Cc: Christoph Hellwig , Keith Busch , Sagi Grimberg , linux-crypto@vger.kernel.org, linux-nvme@lists.infradead.org Subject: Re: [PATCH 1/9] crypto,fs: Separate out hkdf_extract() and hkdf_expand() Message-ID: <20240723013602.GA2319848@google.com> References: <20240722142122.128258-1-hare@kernel.org> <20240722142122.128258-2-hare@kernel.org> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240722142122.128258-2-hare@kernel.org> On Mon, Jul 22, 2024 at 04:21:14PM +0200, Hannes Reinecke wrote: > diff --git a/crypto/Makefile b/crypto/Makefile > index edbbaa3ffef5..b77fc360f0ff 100644 > --- a/crypto/Makefile > +++ b/crypto/Makefile > @@ -29,6 +29,7 @@ obj-$(CONFIG_CRYPTO_ECHAINIV) += echainiv.o > > crypto_hash-y += ahash.o > crypto_hash-y += shash.o > +crypto_hash-y += hkdf.o > obj-$(CONFIG_CRYPTO_HASH2) += crypto_hash.o This should go under a kconfig option CONFIG_CRYPTO_HKDF that is selected by the users that need it. That way the code will be built only when needed. Including a self-test would also be desirable. > diff --git a/crypto/hkdf.c b/crypto/hkdf.c > new file mode 100644 > index 000000000000..22e343851c0b > --- /dev/null > +++ b/crypto/hkdf.c > @@ -0,0 +1,112 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Implementation of HKDF ("HMAC-based Extract-and-Expand Key Derivation > + * Function"), aka RFC 5869. See also the original paper (Krawczyk 2010): > + * "Cryptographic Extraction and Key Derivation: The HKDF Scheme". > + * > + * This is used to derive keys from the fscrypt master keys. This is no longer in fs/crypto/, so the part about fscrypt should be removed. > +/* > + * HKDF consists of two steps: > + * > + * 1. HKDF-Extract: extract a pseudorandom key of length HKDF_HASHLEN bytes from > + * the input keying material and optional salt. It doesn't make sense to refer to HKDF_HASHLEN here since it is specific to fs/crypto/. > +/* HKDF-Extract (RFC 5869 section 2.2), unsalted */ > +int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm, > + unsigned int ikmlen, u8 *prk) Needs kerneldoc now that this is a library interface. > +{ > + unsigned int prklen = crypto_shash_digestsize(hmac_tfm); > + u8 *default_salt; > + int err; > + > + default_salt = kzalloc(prklen, GFP_KERNEL); > + if (!default_salt) > + return -ENOMEM; Now that this is a library interface, it should take the salt as a parameter, and the users who want the default salt should explicitly specify that. If we only provide support for unsalted use, that might inadventently discourage the use of a salt in future code. As the function is named hkdf_extract(), people might also overlook that it's unsalted and doesn't actually match the RFC's definition of HKDF-Extract. The use of kzalloc here is also inefficient, as the maximum length of a digest is known (HKDF_HASHLEN in fs/crypto/ case, HASH_MAX_DIGESTSIZE in general). > + err = crypto_shash_setkey(hmac_tfm, default_salt, prklen); > + if (!err) > + err = crypto_shash_tfm_digest(hmac_tfm, ikm, ikmlen, prk); > + > + kfree(default_salt); > + return err; > +} > +EXPORT_SYMBOL_GPL(hkdf_extract); > + > +/* > + * HKDF-Expand (RFC 5869 section 2.3). > + * This expands the pseudorandom key, which was already keyed into @hmac_tfm, > + * into @okmlen bytes of output keying material parameterized by the > + * application-specific @info of length @infolen bytes. > + * This is thread-safe and may be called by multiple threads in parallel. > + */ > +int hkdf_expand(struct crypto_shash *hmac_tfm, > + const u8 *info, unsigned int infolen, > + u8 *okm, unsigned int okmlen) Needs kerneldoc now that this is a library interface. > diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c > index 5a384dad2c72..9c2f9aca9412 100644 > --- a/fs/crypto/hkdf.c > +++ b/fs/crypto/hkdf.c >// SPDX-License-Identifier: GPL-2.0 >/* > * Implementation of HKDF ("HMAC-based Extract-and-Expand Key Derivation > * Function"), aka RFC 5869. See also the original paper (Krawczyk 2010): > * "Cryptographic Extraction and Key Derivation: The HKDF Scheme". > * > * This is used to derive keys from the fscrypt master keys. > * > * Copyright 2019 Google LLC > */ The above file comment should be adjusted now that this file doesn't contain the actual HKDF implementation. > @@ -118,61 +105,24 @@ int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context, > u8 *okm, unsigned int okmlen) > { > SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm); > - u8 prefix[9]; > - unsigned int i; > + u8 *prefix; > int err; > - const u8 *prev = NULL; > - u8 counter = 1; > - u8 tmp[HKDF_HASHLEN]; > > if (WARN_ON_ONCE(okmlen > 255 * HKDF_HASHLEN)) > return -EINVAL; > > + prefix = kzalloc(okmlen + 9, GFP_KERNEL); > + if (!prefix) > + return -ENOMEM; > desc->tfm = hkdf->hmac_tfm; > > memcpy(prefix, "fscrypt\0", 8); > prefix[8] = context; > + memcpy(prefix + 9, info, infolen); This makes the variable called 'prefix' no longer be the prefix, but rather the full info string. A better name for it would be 'full_info'. Also, it's being allocated with the wrong length. It should be 9 + infolen. > + err = hkdf_expand(hkdf->hmac_tfm, prefix, infolen + 8, > + okm, okmlen); > + kfree(prefix); kfree_sensitive() > diff --git a/include/crypto/hkdf.h b/include/crypto/hkdf.h > new file mode 100644 > index 000000000000..bf06c080d7ed > --- /dev/null > +++ b/include/crypto/hkdf.h > @@ -0,0 +1,18 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +/* > + * HKDF: HMAC-based Key Derivation Function (HKDF), RFC 5869 > + * > + * Extracted from fs/crypto/hkdf.c, which has > + * Copyright 2019 Google LLC > + */ If this is keeping the copyright of fs/crypto/hkdf.c, the license needs to stay the same (GPL-2.0, not GPL-2.0-or-later). - Eric