[PATCH v2 4/8] lib: crypto: import pkcs7_verify.c from linux

[AKASHI Takahiro]

Heinrich,

On Tue, Jul 07, 2020 at 12:27:49PM +0200, Heinrich Schuchardt wrote:
> On 16.06.20 07:26, AKASHI Takahiro wrote:
> > The file, pkcs7_verify.c, will now be imported from linux code and
> > modified to fit into U-Boot environment.
> >
> > In particular, pkcs7_verify_one() function will be used in a later patch
> > to rework signature verification logic aiming to support intermediate
> > certificates in "chain of trust."
> >
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> > ---
> >  lib/crypto/Kconfig        |   3 +
> >  lib/crypto/Makefile       |   1 +
> >  lib/crypto/pkcs7_verify.c | 524 ++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 528 insertions(+)
> >  create mode 100644 lib/crypto/pkcs7_verify.c
> >
> > diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig
> > index 2b221b915aa6..6369bafac07b 100644
> > --- a/lib/crypto/Kconfig
> > +++ b/lib/crypto/Kconfig
> > @@ -49,4 +49,7 @@ config PKCS7_MESSAGE_PARSER
> >  	  This option provides support for parsing PKCS#7 format messages for
> >  	  signature data and provides the ability to verify the signature.
> >
> > +config PKCS7_VERIFY
> > +	bool
> > +
> >  endif # ASYMMETRIC_KEY_TYPE
> > diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
> > index 8267fee0a7b8..f3a414525d2a 100644
> > --- a/lib/crypto/Makefile
> > +++ b/lib/crypto/Makefile
> > @@ -44,6 +44,7 @@ obj-$(CONFIG_PKCS7_MESSAGE_PARSER) += pkcs7_message.o
> >  pkcs7_message-y := \
> >  	pkcs7.asn1.o \
> >  	pkcs7_parser.o
> > +obj-$(CONFIG_PKCS7_VERIFY) += pkcs7_verify.o
> >
> >  $(obj)/pkcs7_parser.o: $(obj)/pkcs7.asn1.h
> >  $(obj)/pkcs7.asn1.o: $(obj)/pkcs7.asn1.c $(obj)/pkcs7.asn1.h
> > diff --git a/lib/crypto/pkcs7_verify.c b/lib/crypto/pkcs7_verify.c
> > new file mode 100644
> > index 000000000000..1e8600f7faca
> > --- /dev/null
> > +++ b/lib/crypto/pkcs7_verify.c
> > @@ -0,0 +1,524 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/* Verify the signature on a PKCS#7 message.
> > + *
> > + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> > + * Written by David Howells (dhowells at redhat.com)
> 
> Please, describe the source from where you copied here:
> 
> Copied from Linux crypto/asymmetric_keys/pkcs7_verify.c.

Okay though I've never seen similar comments when other files
under lib/crypto were imported from linux.

> > + */
> > +
> > +#define pr_fmt(fmt) "PKCS7: "fmt
> 
> This define is really meant to create unreadable code.
> 
> > +#ifdef __UBOOT__
> 
> Who needs those #ifdefs?
> 
> If you really think they are necessary to resync with the Linux code,
> minimize them. One #ifdef for all headers should be enough.
> 
> > +#include <string.h>
> > +#include <linux/bitops.h>
> > +#include <linux/compat.h>
> > +#else
> > +#include <linux/kernel.h>
> > +#include <linux/export.h>
> > +#include <linux/slab.h>
> > +#include <linux/err.h>
> > +#endif
> > +#include <linux/asn1.h>
> > +#ifndef __UBOOT__
> > +#include <crypto/hash.h>
> > +#include <crypto/hash_info.h>
> > +#endif
> > +#include <crypto/public_key.h>
> > +#ifdef __UBOOT__
> > +#include <crypto/pkcs7_parser.h>
> > +#else
> > +#include "pkcs7_parser.h"
> > +#endif

Okay, I will squash them.

> > +
> > +/*
> > + * Digest the relevant parts of the PKCS#7 data
> > + */
> > +#ifdef __UBOOT__
> > +static int pkcs7_digest(struct pkcs7_message *pkcs7,
> > +			struct pkcs7_signed_info *sinfo)
> > +{
> > +	return 0;
> > +}
> > +#else
> > +static int pkcs7_digest(struct pkcs7_message *pkcs7,
> > +			struct pkcs7_signed_info *sinfo)
> > +{
> > +	struct public_key_signature *sig = sinfo->sig;
> > +	struct crypto_shash *tfm;
> > +	struct shash_desc *desc;
> > +	size_t desc_size;
> > +	int ret;
> > +
> > +	kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
> 
> Please, use our logging function: log_content(). At least where you
> defined kenter or pr_devel.

Again, no.
Please read my comment in patch 3/8.

-Takahiro Akashi

> Best regards
> 
> Heinrich
> 
> > +
> > +	/* The digest was calculated already. */
> > +	if (sig->digest)
> > +		return 0;
> > +
> > +	if (!sinfo->sig->hash_algo)
> > +		return -ENOPKG;
> > +
> > +	/* Allocate the hashing algorithm we're going to need and find out how
> > +	 * big the hash operational data will be.
> > +	 */
> > +	tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
> > +	if (IS_ERR(tfm))
> > +		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
> > +
> > +	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
> > +	sig->digest_size = crypto_shash_digestsize(tfm);
> > +
> > +	ret = -ENOMEM;
> > +	sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
> > +	if (!sig->digest)
> > +		goto error_no_desc;
> > +
> > +	desc = kzalloc(desc_size, GFP_KERNEL);
> > +	if (!desc)
> > +		goto error_no_desc;
> > +
> > +	desc->tfm   = tfm;
> > +
> > +	/* Digest the message [RFC2315 9.3] */
> > +	ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
> > +				  sig->digest);
> > +	if (ret < 0)
> > +		goto error;
> > +	pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
> > +
> > +	/* However, if there are authenticated attributes, there must be a
> > +	 * message digest attribute amongst them which corresponds to the
> > +	 * digest we just calculated.
> > +	 */
> > +	if (sinfo->authattrs) {
> > +		u8 tag;
> > +
> > +		if (!sinfo->msgdigest) {
> > +			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
> > +			ret = -EKEYREJECTED;
> > +			goto error;
> > +		}
> > +
> > +		if (sinfo->msgdigest_len != sig->digest_size) {
> > +			pr_debug("Sig %u: Invalid digest size (%u)\n",
> > +				 sinfo->index, sinfo->msgdigest_len);
> > +			ret = -EBADMSG;
> > +			goto error;
> > +		}
> > +
> > +		if (memcmp(sig->digest, sinfo->msgdigest,
> > +			   sinfo->msgdigest_len) != 0) {
> > +			pr_debug("Sig %u: Message digest doesn't match\n",
> > +				 sinfo->index);
> > +			ret = -EKEYREJECTED;
> > +			goto error;
> > +		}
> > +
> > +		/* We then calculate anew, using the authenticated attributes
> > +		 * 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.
> > +		 */
> > +		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;
> > +		pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
> > +	}
> > +
> > +error:
> > +	kfree(desc);
> > +error_no_desc:
> > +	crypto_free_shash(tfm);
> > +	kleave(" = %d", ret);
> > +	return ret;
> > +}
> > +
> > +int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
> > +		     enum hash_algo *hash_algo)
> > +{
> > +	struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
> > +	int i, ret;
> > +
> > +	/*
> > +	 * This function doesn't support messages with more than one signature.
> > +	 */
> > +	if (sinfo == NULL || sinfo->next != NULL)
> > +		return -EBADMSG;
> > +
> > +	ret = pkcs7_digest(pkcs7, sinfo);
> > +	if (ret)
> > +		return ret;
> > +
> > +	*buf = sinfo->sig->digest;
> > +	*len = sinfo->sig->digest_size;
> > +
> > +	for (i = 0; i < HASH_ALGO__LAST; i++)
> > +		if (!strcmp(hash_algo_name[i], sinfo->sig->hash_algo)) {
> > +			*hash_algo = i;
> > +			break;
> > +		}
> > +
> > +	return 0;
> > +}
> > +#endif /* !__UBOOT__ */
> > +
> > +/*
> > + * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
> > + * uses the issuer's name and the issuing certificate serial number for
> > + * matching purposes.  These must match the certificate issuer's name (not
> > + * subject's name) and the certificate serial number [RFC 2315 6.7].
> > + */
> > +static int pkcs7_find_key(struct pkcs7_message *pkcs7,
> > +			  struct pkcs7_signed_info *sinfo)
> > +{
> > +	struct x509_certificate *x509;
> > +	unsigned certix = 1;
> > +
> > +	kenter("%u", sinfo->index);
> > +
> > +	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
> > +		/* I'm _assuming_ that the generator of the PKCS#7 message will
> > +		 * encode the fields from the X.509 cert in the same way in the
> > +		 * PKCS#7 message - but I can't be 100% sure of that.  It's
> > +		 * possible this will need element-by-element comparison.
> > +		 */
> > +		if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
> > +			continue;
> > +		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
> > +			 sinfo->index, certix);
> > +
> > +		if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
> > +			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
> > +				sinfo->index);
> > +			continue;
> > +		}
> > +
> > +		sinfo->signer = x509;
> > +		return 0;
> > +	}
> > +
> > +	/* The relevant X.509 cert isn't found here, but it might be found in
> > +	 * the trust keyring.
> > +	 */
> > +	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
> > +		 sinfo->index,
> > +		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
> > +	return 0;
> > +}
> > +
> > +/*
> > + * Verify the internal certificate chain as best we can.
> > + */
> > +static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
> > +				  struct pkcs7_signed_info *sinfo)
> > +{
> > +	struct public_key_signature *sig;
> > +	struct x509_certificate *x509 = sinfo->signer, *p;
> > +	struct asymmetric_key_id *auth;
> > +	int ret;
> > +
> > +	kenter("");
> > +
> > +	for (p = pkcs7->certs; p; p = p->next)
> > +		p->seen = false;
> > +
> > +	for (;;) {
> > +		pr_debug("verify %s: %*phN\n",
> > +			 x509->subject,
> > +			 x509->raw_serial_size, x509->raw_serial);
> > +		x509->seen = true;
> > +
> > +		if (x509->blacklisted) {
> > +			/* If this cert is blacklisted, then mark everything
> > +			 * that depends on this as blacklisted too.
> > +			 */
> > +			sinfo->blacklisted = true;
> > +			for (p = sinfo->signer; p != x509; p = p->signer)
> > +				p->blacklisted = true;
> > +			pr_debug("- blacklisted\n");
> > +			return 0;
> > +		}
> > +
> > +		if (x509->unsupported_key)
> > +			goto unsupported_crypto_in_x509;
> > +
> > +		pr_debug("- issuer %s\n", x509->issuer);
> > +		sig = x509->sig;
> > +		if (sig->auth_ids[0])
> > +			pr_debug("- authkeyid.id %*phN\n",
> > +				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
> > +		if (sig->auth_ids[1])
> > +			pr_debug("- authkeyid.skid %*phN\n",
> > +				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
> > +
> > +		if (x509->self_signed) {
> > +			/* If there's no authority certificate specified, then
> > +			 * the certificate must be self-signed and is the root
> > +			 * of the chain.  Likewise if the cert is its own
> > +			 * authority.
> > +			 */
> > +			if (x509->unsupported_sig)
> > +				goto unsupported_crypto_in_x509;
> > +			x509->signer = x509;
> > +			pr_debug("- self-signed\n");
> > +			return 0;
> > +		}
> > +
> > +		/* Look through the X.509 certificates in the PKCS#7 message's
> > +		 * list to see if the next one is there.
> > +		 */
> > +		auth = sig->auth_ids[0];
> > +		if (auth) {
> > +			pr_debug("- want %*phN\n", auth->len, auth->data);
> > +			for (p = pkcs7->certs; p; p = p->next) {
> > +				pr_debug("- cmp [%u] %*phN\n",
> > +					 p->index, p->id->len, p->id->data);
> > +				if (asymmetric_key_id_same(p->id, auth))
> > +					goto found_issuer_check_skid;
> > +			}
> > +		} else if (sig->auth_ids[1]) {
> > +			auth = sig->auth_ids[1];
> > +			pr_debug("- want %*phN\n", auth->len, auth->data);
> > +			for (p = pkcs7->certs; p; p = p->next) {
> > +				if (!p->skid)
> > +					continue;
> > +				pr_debug("- cmp [%u] %*phN\n",
> > +					 p->index, p->skid->len, p->skid->data);
> > +				if (asymmetric_key_id_same(p->skid, auth))
> > +					goto found_issuer;
> > +			}
> > +		}
> > +
> > +		/* We didn't find the root of this chain */
> > +		pr_debug("- top\n");
> > +		return 0;
> > +
> > +	found_issuer_check_skid:
> > +		/* We matched issuer + serialNumber, but if there's an
> > +		 * authKeyId.keyId, that must match the CA subjKeyId also.
> > +		 */
> > +		if (sig->auth_ids[1] &&
> > +		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
> > +			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
> > +				sinfo->index, x509->index, p->index);
> > +			return -EKEYREJECTED;
> > +		}
> > +	found_issuer:
> > +		pr_debug("- subject %s\n", p->subject);
> > +		if (p->seen) {
> > +			pr_warn("Sig %u: X.509 chain contains loop\n",
> > +				sinfo->index);
> > +			return 0;
> > +		}
> > +		ret = public_key_verify_signature(p->pub, x509->sig);
> > +		if (ret < 0)
> > +			return ret;
> > +		x509->signer = p;
> > +		if (x509 == p) {
> > +			pr_debug("- self-signed\n");
> > +			return 0;
> > +		}
> > +		x509 = p;
> > +#ifndef __UBOOT__
> > +		might_sleep();
> > +#endif
> > +	}
> > +
> > +unsupported_crypto_in_x509:
> > +	/* Just prune the certificate chain at this point if we lack some
> > +	 * crypto module to go further.  Note, however, we don't want to set
> > +	 * sinfo->unsupported_crypto as the signed info block may still be
> > +	 * validatable against an X.509 cert lower in the chain that we have a
> > +	 * trusted copy of.
> > +	 */
> > +	return 0;
> > +}
> > +
> > +/*
> > + * Verify one signed information block from a PKCS#7 message.
> > + */
> > +#ifndef __UBOOT__
> > +static
> > +#endif
> > +int pkcs7_verify_one(struct pkcs7_message *pkcs7,
> > +		     struct pkcs7_signed_info *sinfo)
> > +{
> > +	int ret;
> > +
> > +	kenter(",%u", sinfo->index);
> > +
> > +	/* First of all, digest the data in the PKCS#7 message and the
> > +	 * signed information block
> > +	 */
> > +	ret = pkcs7_digest(pkcs7, sinfo);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	/* Find the key for the signature if there is one */
> > +	ret = pkcs7_find_key(pkcs7, sinfo);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	if (!sinfo->signer)
> > +		return 0;
> > +
> > +	pr_devel("Using X.509[%u] for sig %u\n",
> > +		 sinfo->signer->index, sinfo->index);
> > +
> > +	/* Check that the PKCS#7 signing time is valid according to the X.509
> > +	 * certificate.  We can't, however, check against the system clock
> > +	 * since that may not have been set yet and may be wrong.
> > +	 */
> > +	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
> > +		if (sinfo->signing_time < sinfo->signer->valid_from ||
> > +		    sinfo->signing_time > sinfo->signer->valid_to) {
> > +			pr_warn("Message signed outside of X.509 validity window\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +	}
> > +
> > +	/* Verify the PKCS#7 binary against the key */
> > +	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	pr_devel("Verified signature %u\n", sinfo->index);
> > +
> > +	/* Verify the internal certificate chain */
> > +	return pkcs7_verify_sig_chain(pkcs7, sinfo);
> > +}
> > +
> > +#ifndef __UBOOT__
> > +/**
> > + * pkcs7_verify - Verify a PKCS#7 message
> > + * @pkcs7: The PKCS#7 message to be verified
> > + * @usage: The use to which the key is being put
> > + *
> > + * Verify a PKCS#7 message is internally consistent - that is, the data digest
> > + * matches the digest in the AuthAttrs and any signature in the message or one
> > + * of the X.509 certificates it carries that matches another X.509 cert in the
> > + * message can be verified.
> > + *
> > + * This does not look to match the contents of the PKCS#7 message against any
> > + * external public keys.
> > + *
> > + * Returns, in order of descending priority:
> > + *
> > + *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
> > + *      odds with the specified usage, or:
> > + *
> > + *  (*) -EKEYREJECTED if a signature failed to match for which we found an
> > + *	appropriate X.509 certificate, or:
> > + *
> > + *  (*) -EBADMSG if some part of the message was invalid, or:
> > + *
> > + *  (*) 0 if a signature chain passed verification, or:
> > + *
> > + *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
> > + *
> > + *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
> > + *	crypto modules couldn't be found.
> > + */
> > +int pkcs7_verify(struct pkcs7_message *pkcs7,
> > +		 enum key_being_used_for usage)
> > +{
> > +	struct pkcs7_signed_info *sinfo;
> > +	int actual_ret = -ENOPKG;
> > +	int ret;
> > +
> > +	kenter("");
> > +
> > +	switch (usage) {
> > +	case VERIFYING_MODULE_SIGNATURE:
> > +		if (pkcs7->data_type != OID_data) {
> > +			pr_warn("Invalid module sig (not pkcs7-data)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		if (pkcs7->have_authattrs) {
> > +			pr_warn("Invalid module sig (has authattrs)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		break;
> > +	case VERIFYING_FIRMWARE_SIGNATURE:
> > +		if (pkcs7->data_type != OID_data) {
> > +			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		if (!pkcs7->have_authattrs) {
> > +			pr_warn("Invalid firmware sig (missing authattrs)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		break;
> > +	case VERIFYING_KEXEC_PE_SIGNATURE:
> > +		if (pkcs7->data_type != OID_msIndirectData) {
> > +			pr_warn("Invalid kexec sig (not Authenticode)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		/* Authattr presence checked in parser */
> > +		break;
> > +	case VERIFYING_UNSPECIFIED_SIGNATURE:
> > +		if (pkcs7->data_type != OID_data) {
> > +			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
> > +			return -EKEYREJECTED;
> > +		}
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +
> > +	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
> > +		ret = pkcs7_verify_one(pkcs7, sinfo);
> > +		if (sinfo->blacklisted) {
> > +			if (actual_ret == -ENOPKG)
> > +				actual_ret = -EKEYREJECTED;
> > +			continue;
> > +		}
> > +		if (ret < 0) {
> > +			if (ret == -ENOPKG) {
> > +				sinfo->unsupported_crypto = true;
> > +				continue;
> > +			}
> > +			kleave(" = %d", ret);
> > +			return ret;
> > +		}
> > +		actual_ret = 0;
> > +	}
> > +
> > +	kleave(" = %d", actual_ret);
> > +	return actual_ret;
> > +}
> > +EXPORT_SYMBOL_GPL(pkcs7_verify);
> > +
> > +/**
> > + * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
> > + * @pkcs7: The PKCS#7 message
> > + * @data: The data to be verified
> > + * @datalen: The amount of data
> > + *
> > + * Supply the detached data needed to verify a PKCS#7 message.  Note that no
> > + * attempt to retain/pin the data is made.  That is left to the caller.  The
> > + * data will not be modified by pkcs7_verify() and will not be freed when the
> > + * PKCS#7 message is freed.
> > + *
> > + * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
> > + */
> > +int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
> > +			       const void *data, size_t datalen)
> > +{
> > +	if (pkcs7->data) {
> > +		pr_debug("Data already supplied\n");
> > +		return -EINVAL;
> > +	}
> > +	pkcs7->data = data;
> > +	pkcs7->data_len = datalen;
> > +	return 0;
> > +}
> > +#endif /* __UBOOT__ */
> >
>