[PATCH v13 07/20] appended signatures: Parse PKCS#7 signed data

[Sudhakar Kuppusamy <sudhakar@linux.ibm.com>]

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: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/commands/appendedsig/appendedsig.h |  37 ++
 grub-core/commands/appendedsig/pkcs7.c       | 452 +++++++++++++++++++
 2 files changed, 489 insertions(+)
 create mode 100644 grub-core/commands/appendedsig/pkcs7.c

diff --git a/grub-core/commands/appendedsig/appendedsig.h b/grub-core/commands/appendedsig/appendedsig.h
index 601d6164f..b0beb8935 100644
--- a/grub-core/commands/appendedsig/appendedsig.h
+++ b/grub-core/commands/appendedsig/appendedsig.h
@@ -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);
diff --git a/grub-core/commands/appendedsig/pkcs7.c b/grub-core/commands/appendedsig/pkcs7.c
new file mode 100644
index 000000000..b8e272047
--- /dev/null
+++ b/grub-core/commands/appendedsig/pkcs7.c
@@ -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);
+}
-- 
2.50.1 (Apple Git-155)


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