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appended signatures: Parse PKCS#7 signed data

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This code allows us to parse:

 - PKCS#7 signed data messages. Only a single signer info is supported, which
   is all that the Linux sign-file utility supports creating out-of-the-box.
   Only RSA, SHA-256 and SHA-512 are supported. Any certificate embedded in
   the PKCS#7 message will be ignored.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Sudhakar Kuppusamy 2025-10-06 12:54:52 +05:30 committed by Daniel Kiper
parent 3e4ff6ffb3
commit a337549797
2 changed files with 489 additions and 0 deletions
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37
grub-core/commands/appendedsig/appendedsig.h
View File

@ -17,11 +17,48 @@
* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
#include <grub/crypto.h>
#include <libtasn1.h>
extern asn1_node grub_gnutls_gnutls_asn;
extern asn1_node grub_gnutls_pkix_asn;
#define GRUB_MAX_OID_LEN 32
/* A PKCS#7 signed data signer info. */
struct pkcs7_signer
{
const gcry_md_spec_t *hash;
gcry_mpi_t sig_mpi;
};
typedef struct pkcs7_signer grub_pkcs7_signer_t;
/*
* A PKCS#7 signed data message. We make no attempt to match intelligently, so
* we don't save any info about the signer.
*/
struct pkcs7_data
{
grub_int32_t signer_count;
grub_pkcs7_signer_t *signers;
};
typedef struct pkcs7_data grub_pkcs7_data_t;
/*
* Parse a PKCS#7 message, which must be a signed data message. The message must
* be in 'sigbuf' and of size 'data_size'. The result is placed in 'msg', which
* must already be allocated.
*/
extern grub_err_t
grub_pkcs7_data_parse (const void *sigbuf, grub_size_t data_size, grub_pkcs7_data_t *msg);
/*
* Release all the storage associated with the PKCS#7 message. If the caller
* dynamically allocated the message, it must free it.
*/
extern void
grub_pkcs7_data_release (grub_pkcs7_data_t *msg);
/* Do libtasn1 init. */
extern int
grub_asn1_init (void);

452
grub-core/commands/appendedsig/pkcs7.c Normal file
View File

@ -0,0 +1,452 @@
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2020, 2022 Free Software Foundation, Inc.
* Copyright (C) 2020, 2022, 2025 IBM Corporation
*
* GRUB is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GRUB is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
#include "appendedsig.h"
#include <grub/misc.h>
#include <grub/crypto.h>
#include <grub/gcrypt/gcrypt.h>
#include <sys/types.h>
static char asn1_error[ASN1_MAX_ERROR_DESCRIPTION_SIZE];
/* RFC 5652 s 5.1. */
static const char *signedData_oid = "1.2.840.113549.1.7.2";
/* RFC 4055 s 2.1. */
static const char *sha256_oid = "2.16.840.1.101.3.4.2.1";
static const char *sha512_oid = "2.16.840.1.101.3.4.2.3";
static grub_err_t
process_content (grub_uint8_t *content, grub_int32_t size, grub_pkcs7_data_t *msg)
{
grub_int32_t res;
asn1_node signed_part;
grub_err_t err = GRUB_ERR_NONE;
char algo_oid[GRUB_MAX_OID_LEN];
grub_int32_t algo_oid_size;
grub_int32_t algo_count;
grub_int32_t signer_count;
grub_int32_t i;
char version;
grub_int32_t version_size = sizeof (version);
grub_uint8_t *result_buf;
grub_int32_t result_size = 0;
grub_int32_t crls_size = 0;
gcry_error_t gcry_err;
bool sha256_in_da, sha256_in_si, sha512_in_da, sha512_in_si;
char *da_path;
char *si_sig_path;
char *si_da_path;
res = asn1_create_element (grub_gnutls_pkix_asn, "PKIX1.pkcs-7-SignedData", &signed_part);
if (res != ASN1_SUCCESS)
return grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not create ASN.1 structure for PKCS#7 signed part");
res = asn1_der_decoding2 (&signed_part, content, &size,
ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"error reading PKCS#7 signed data: %s", asn1_error);
goto cleanup_signed_part;
}
/*
* SignedData ::= SEQUENCE {
* version CMSVersion,
* digestAlgorithms DigestAlgorithmIdentifiers,
* encapContentInfo EncapsulatedContentInfo,
* certificates [0] IMPLICIT CertificateSet OPTIONAL,
* crls [1] IMPLICIT RevocationInfoChoices OPTIONAL,
* signerInfos SignerInfos }
*/
res = asn1_read_value (signed_part, "version", &version, &version_size);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "error reading signedData version: %s",
asn1_strerror (res));
goto cleanup_signed_part;
}
/* Signature version must be 1 because appended signature only support v1. */
if (version != 1)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"unexpected signature version v%d, only v1 supported", version);
goto cleanup_signed_part;
}
/*
* digestAlgorithms DigestAlgorithmIdentifiers
*
* DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
* DigestAlgorithmIdentifer is an X.509 AlgorithmIdentifier (10.1.1)
*
* RFC 4055 s 2.1:
* sha256Identifier AlgorithmIdentifier ::= { id-sha256, NULL }
* sha512Identifier AlgorithmIdentifier ::= { id-sha512, NULL }
*
* We only support 1 element in the set, and we do not check parameters atm.
*/
res = asn1_number_of_elements (signed_part, "digestAlgorithms", &algo_count);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "error counting number of digest algorithms: %s",
asn1_strerror (res));
goto cleanup_signed_part;
}
if (algo_count <= 0)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "a minimum of 1 digest algorithm is required");
goto cleanup_signed_part;
}
if (algo_count > 2)
{
err = grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET, "a maximum of 2 digest algorithms is supported");
goto cleanup_signed_part;
}
sha256_in_da = false;
sha512_in_da = false;
for (i = 0; i < algo_count; i++)
{
da_path = grub_xasprintf ("digestAlgorithms.?%d.algorithm", i + 1);
if (da_path == NULL)
{
err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not allocate path for digest algorithm parsing path");
goto cleanup_signed_part;
}
algo_oid_size = sizeof (algo_oid);
res = asn1_read_value (signed_part, da_path, algo_oid, &algo_oid_size);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "error reading digest algorithm: %s",
asn1_strerror (res));
grub_free (da_path);
goto cleanup_signed_part;
}
if (grub_strncmp (sha512_oid, algo_oid, algo_oid_size) == 0)
{
if (sha512_in_da == false)
sha512_in_da = true;
else
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"SHA-512 specified twice in digest algorithm list");
grub_free (da_path);
goto cleanup_signed_part;
}
}
else if (grub_strncmp (sha256_oid, algo_oid, algo_oid_size) == 0)
{
if (sha256_in_da == false)
sha256_in_da = true;
else
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"SHA-256 specified twice in digest algorithm list");
grub_free (da_path);
goto cleanup_signed_part;
}
}
else
{
err = grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
"only SHA-256 and SHA-512 hashes are supported, found OID %s",
algo_oid);
grub_free (da_path);
goto cleanup_signed_part;
}
grub_free (da_path);
}
/* At this point, at least one of sha{256,512}_in_da must be true. */
/*
* We ignore the certificates, but we don't permit CRLs. A CRL entry might be
* revoking the certificate we're using, and we have no way of dealing with
* that at the moment.
*/
res = asn1_read_value (signed_part, "crls", NULL, &crls_size);
if (res != ASN1_ELEMENT_NOT_FOUND)
{
err = grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
"PKCS#7 messages with embedded CRLs are not supported");
goto cleanup_signed_part;
}
/* Read the signatures */
res = asn1_number_of_elements (signed_part, "signerInfos", &signer_count);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "error counting number of signers: %s",
asn1_strerror (res));
goto cleanup_signed_part;
}
if (signer_count <= 0)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "a minimum of 1 signer is required");
goto cleanup_signed_part;
}
msg->signers = grub_calloc (signer_count, sizeof (grub_pkcs7_signer_t));
if (msg->signers == NULL)
{
err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not allocate space for %d signers", signer_count);
goto cleanup_signed_part;
}
msg->signer_count = 0;
for (i = 0; i < signer_count; i++)
{
si_da_path = grub_xasprintf ("signerInfos.?%d.digestAlgorithm.algorithm", i + 1);
if (si_da_path == NULL)
{
err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not allocate path for signer %d's digest algorithm parsing path",
i);
goto cleanup_signerInfos;
}
algo_oid_size = sizeof (algo_oid);
res = asn1_read_value (signed_part, si_da_path, algo_oid, &algo_oid_size);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"error reading signer %d's digest algorithm: %s", i, asn1_strerror (res));
grub_free (si_da_path);
goto cleanup_signerInfos;
}
grub_free (si_da_path);
if (grub_strncmp (sha512_oid, algo_oid, algo_oid_size) == 0)
{
if (sha512_in_da == false)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"signer %d claims a SHA-512 signature which was not "
"specified in the outer DigestAlgorithms", i);
goto cleanup_signerInfos;
}
else
{
sha512_in_si = true;
msg->signers[i].hash = grub_crypto_lookup_md_by_name ("sha512");
}
}
else if (grub_strncmp (sha256_oid, algo_oid, algo_oid_size) == 0)
{
if (sha256_in_da == false)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"signer %d claims a SHA-256 signature which was not "
"specified in the outer DigestAlgorithms", i);
goto cleanup_signerInfos;
}
else
{
sha256_in_si = true;
msg->signers[i].hash = grub_crypto_lookup_md_by_name ("sha256");
}
}
else
{
err = grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
"only SHA-256 and SHA-512 hashes are supported, found OID %s",
algo_oid);
goto cleanup_signerInfos;
}
if (msg->signers[i].hash == NULL)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"Hash algorithm for signer %d (OID %s) not loaded", i, algo_oid);
goto cleanup_signerInfos;
}
si_sig_path = grub_xasprintf ("signerInfos.?%d.signature", i + 1);
if (si_sig_path == NULL)
{
err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not allocate path for signer %d's signature parsing path", i);
goto cleanup_signerInfos;
}
result_buf = grub_asn1_allocate_and_read (signed_part, si_sig_path, "signature data", &result_size);
grub_free (si_sig_path);
if (result_buf == NULL)
{
err = grub_errno;
goto cleanup_signerInfos;
}
gcry_err = _gcry_mpi_scan (&(msg->signers[i].sig_mpi), GCRYMPI_FMT_USG,
result_buf, result_size, NULL);
grub_free (result_buf);
if (gcry_err != GPG_ERR_NO_ERROR)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"error loading signature %d into MPI structure: %d",
i, gcry_err);
goto cleanup_signerInfos;
}
/*
* Use msg->signer_count to track fully populated signerInfos so we know
* how many we need to clean up.
*/
msg->signer_count++;
}
/*
* Final consistency check of signerInfo.*.digestAlgorithm vs digestAlgorithms
* .*.algorithm. An algorithm must be present in both digestAlgorithms and
* signerInfo or in neither. We have already checked for an algorithm in
* signerInfo that is not in digestAlgorithms, here we check for algorithms in
* digestAlgorithms but not in signerInfos.
*/
if (sha512_in_da == true && sha512_in_si == false)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"SHA-512 specified in DigestAlgorithms but did not appear in SignerInfos");
goto cleanup_signerInfos;
}
if (sha256_in_da == true && sha256_in_si == false)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"SHA-256 specified in DigestAlgorithms but did not appear in SignerInfos");
goto cleanup_signerInfos;
}
asn1_delete_structure (&signed_part);
return GRUB_ERR_NONE;
cleanup_signerInfos:
for (i = 0; i < msg->signer_count; i++)
_gcry_mpi_release (msg->signers[i].sig_mpi);
grub_free (msg->signers);
cleanup_signed_part:
asn1_delete_structure (&signed_part);
return err;
}
grub_err_t
grub_pkcs7_data_parse (const void *sigbuf, grub_size_t data_size, grub_pkcs7_data_t *msg)
{
grub_int32_t res;
asn1_node content_info;
grub_err_t err = GRUB_ERR_NONE;
char content_oid[GRUB_MAX_OID_LEN];
grub_uint8_t *content;
grub_int32_t content_size;
grub_int32_t content_oid_size = sizeof (content_oid);
grub_int32_t size = (grub_int32_t) data_size;
if (data_size > GRUB_UINT_MAX)
return grub_error (GRUB_ERR_OUT_OF_RANGE,
"cannot parse a PKCS#7 message where data size > GRUB_UINT_MAX");
res = asn1_create_element (grub_gnutls_pkix_asn, "PKIX1.pkcs-7-ContentInfo", &content_info);
if (res != ASN1_SUCCESS)
return grub_error (GRUB_ERR_OUT_OF_MEMORY,
"could not create ASN.1 structure for PKCS#7 data: %s",
asn1_strerror (res));
res = asn1_der_decoding2 (&content_info, sigbuf, &size,
ASN1_DECODE_FLAG_STRICT_DER | ASN1_DECODE_FLAG_ALLOW_PADDING,
asn1_error);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"error decoding PKCS#7 message DER: %s", asn1_error);
goto cleanup;
}
/*
* ContentInfo ::= SEQUENCE {
* contentType ContentType,
* content [0] EXPLICIT ANY DEFINED BY contentType }
*
* ContentType ::= OBJECT IDENTIFIER
*/
res = asn1_read_value (content_info, "contentType", content_oid, &content_oid_size);
if (res != ASN1_SUCCESS)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE, "error reading PKCS#7 content type: %s",
asn1_strerror (res));
goto cleanup;
}
/* OID for SignedData defined in 5.1. */
if (grub_strncmp (signedData_oid, content_oid, content_oid_size) != 0)
{
err = grub_error (GRUB_ERR_BAD_SIGNATURE,
"unexpected content type in PKCS#7 message: OID %s", content_oid);
goto cleanup;
}
content = grub_asn1_allocate_and_read (content_info, "content", "PKCS#7 message content", &content_size);
if (content == NULL)
{
err = grub_errno;
goto cleanup;
}
err = process_content (content, content_size, msg);
grub_free (content);
cleanup:
asn1_delete_structure (&content_info);
return err;
}
/*
* Release all the storage associated with the PKCS#7 message. If the caller
* dynamically allocated the message, it must free it.
*/
void
grub_pkcs7_data_release (grub_pkcs7_data_t *msg)
{
grub_int32_t i;
for (i = 0; i < msg->signer_count; i++)
_gcry_mpi_release (msg->signers[i].sig_mpi);
grub_free (msg->signers);
}