From: Daniel Axtens <d...@axtens.net>
This code allows us to parse:
- X.509 certificates: at least enough to verify the signatures on the
PKCS#7 messages. We expect that the certificates embedded in grub will
be leaf certificates, not CA certificates. The parser enforces this.
- X.509 certificates support the Extended Key Usage extension and handle
it by verifying that the certificate has a Code Signing usage.
Signed-off-by: Javier Martinez Canillas <javi...@redhat.com> # EKU support
Reported-by: Michal Suchanek <msucha...@suse.com> # key usage issue
Signed-off-by: Daniel Axtens <d...@axtens.net>
Signed-off-by: Sudhakar Kuppusamy <sudha...@linux.ibm.com>
Reviewed-by: Stefan Berger <stef...@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avn...@linux.ibm.com>
---
grub-core/commands/appendedsig/appendedsig.h | 30 +
grub-core/commands/appendedsig/x509.c | 954 +++++++++++++++++++
2 files changed, 984 insertions(+)
create mode 100644 grub-core/commands/appendedsig/x509.c
diff --git a/grub-core/commands/appendedsig/appendedsig.h
b/grub-core/commands/appendedsig/appendedsig.h
index c3dc8a9a9..352eaf64d 100644
--- a/grub-core/commands/appendedsig/appendedsig.h
+++ b/grub-core/commands/appendedsig/appendedsig.h
@@ -25,6 +25,21 @@ extern asn1_node grub_gnutls_pkix_asn;
#define MAX_OID_LEN 32
+/*
+ * One or more x509 certificates.Add commentMore actions
+ * We do limited parsing: extracting only the serial, CN and RSA public key.
+ */
+struct x509_certificate
+{
+ struct x509_certificate *next;
+ grub_uint8_t *serial;
+ grub_size_t serial_len;
+ char *subject;
+ grub_size_t subject_len;
+ /* We only support RSA public keys. This encodes [modulus, publicExponent] */
+ gcry_mpi_t mpis[2];
+};
+
/* A PKCS#7 signedData signerInfo.Add commentMore actions */
struct pkcs7_signerInfo
{
@@ -43,6 +58,21 @@ struct pkcs7_signedData
struct pkcs7_signerInfo *signerInfos;
};
+/*
+ * Import a DER-encoded certificate at 'data', of size 'size'.
+ * Place the results into 'results', which must be already allocated.Add
commentMore actions
+ */
+extern grub_err_t
+parse_x509_certificate (const void *data, grub_size_t size, struct
x509_certificate *results);
+
+/*
+ * Release all the storage associated with the x509 certificate.
+ * If the caller dynamically allocated the certificate, it must free it.
+ * The caller is also responsible for maintenance of the linked list.
+ */
+extern void
+certificate_release (struct x509_certificate *cert);
+
/*
* Parse a PKCS#7 message, which must be a signedData message.Add commentMore
actions
* The message must be in 'sigbuf' and of size 'data_size'. The result is
diff --git a/grub-core/commands/appendedsig/x509.c
b/grub-core/commands/appendedsig/x509.c
new file mode 100644
index 000000000..414f7d101
--- /dev/null
+++ b/grub-core/commands/appendedsig/x509.c
@@ -0,0 +1,954 @@
+/*
+ * 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 <libtasn1.h>
+#include <grub/types.h>
+#include <grub/err.h>
+#include <grub/mm.h>
+#include <grub/crypto.h>
+#include <grub/misc.h>
+#include <grub/gcrypt/gcrypt.h>
+
+#include "appendedsig.h"
+
+static char asn1_error[ASN1_MAX_ERROR_DESCRIPTION_SIZE];
+
+
+/* RFC 3279 2.3.1 RSA Keys */
+static const char *rsaEncryption_oid = "1.2.840.113549.1.1.1";
+
+/* RFC 5280 Appendix A */
+static const char *commonName_oid = "2.5.4.3";
+
+/* RFC 5280 4.2.1.3 Key Usage */
+static const char *keyUsage_oid = "2.5.29.15";
+
+static const grub_uint8_t digitalSignatureUsage = 0x80;
+
+/* RFC 5280 4.2.1.9 Basic Constraints */
+static const char *basicConstraints_oid = "2.5.29.19";
+
+/* RFC 5280 4.2.1.12 Extended Key Usage */
+static const char *extendedKeyUsage_oid = "2.5.29.37";
+static const char *codeSigningUsage_oid = "1.3.6.1.5.5.7.3.3";
+
+/*
+ * RFC 3279 2.3.1
+ *
+ * The RSA public key MUST be encoded using the ASN.1 type RSAPublicKey:
+ *
+ * RSAPublicKey ::= SEQUENCE {
+ * modulus INTEGER, -- n
+ * publicExponent INTEGER } -- e
+ *
+ * where modulus is the modulus n, and publicExponent is the public
+ * exponent e.
+ */
+static grub_err_t
+grub_parse_rsa_pubkey (grub_uint8_t *der, int dersize, struct x509_certificate
*certificate)
+{
+ int result;
+ asn1_node spk = NULL;
+ grub_uint8_t *m_data, *e_data;
+ int m_size, e_size;
+ grub_err_t err = GRUB_ERR_NONE;
+ gcry_error_t gcry_err;
+
+ result = asn1_create_element (grub_gnutls_gnutls_asn, "GNUTLS.RSAPublicKey",
&spk);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ "cannot create storage for public key ASN.1 data");
+
+ result = asn1_der_decoding2 (&spk, der, &dersize,
ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("cannot decode certificate public key DER: %s"),
asn1_error);
+ goto cleanup;
+ }
+
+ m_data = grub_asn1_allocate_and_read (spk, "modulus", "RSA modulus",
&m_size);
+ if (m_data == NULL)
+ {
+ err = grub_errno;
+ goto cleanup;
+ }
+
+ e_data = grub_asn1_allocate_and_read (spk, "publicExponent", "RSA public
exponent", &e_size);
+ if (e_data == NULL)
+ {
+ err = grub_errno;
+ goto cleanup_m_data;
+ }
+
+ /*
+ * convert m, e to mpi
+ *
+ * nscanned is not set for FMT_USG, it's only set for FMT_PGP,
+ * so we can't verify it
+ */
+ gcry_err = gcry_mpi_scan (&certificate->mpis[0], GCRYMPI_FMT_USG, m_data,
m_size, NULL);
+ if (gcry_err != GPG_ERR_NO_ERROR)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error loading RSA modulus into MPI structure:
%d"), gcry_err);
+ goto cleanup_e_data;
+ }
+
+ gcry_err = gcry_mpi_scan (&certificate->mpis[1], GCRYMPI_FMT_USG, e_data,
e_size, NULL);
+ if (gcry_err != GPG_ERR_NO_ERROR)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error loading RSA exponent into MPI structure:
%d"), gcry_err);
+ goto cleanup_m_mpi;
+ }
+
+ grub_free (e_data);
+ grub_free (m_data);
+ asn1_delete_structure (&spk);
+
+ return GRUB_ERR_NONE;
+
+ cleanup_m_mpi:
+ gcry_mpi_release (certificate->mpis[0]);
+ cleanup_e_data:
+ grub_free (e_data);
+ cleanup_m_data:
+ grub_free (m_data);
+ cleanup:
+ asn1_delete_structure (&spk);
+
+ return err;
+}
+
+/*
+ * RFC 5280:
+ * SubjectPublicKeyInfo ::= SEQUENCE {
+ * algorithm AlgorithmIdentifier,
+ * subjectPublicKey BIT STRING }
+ *
+ * AlgorithmIdentifiers come from RFC 3279, we are not strictly compilant as we
+ * only support RSA Encryption.
+ */
+static grub_err_t
+grub_x509_read_subject_public_key (asn1_node asn, struct x509_certificate
*results)
+{
+ int result;
+ grub_err_t err;
+ const char *algo_name =
"tbsCertificate.subjectPublicKeyInfo.algorithm.algorithm";
+ const char *params_name =
"tbsCertificate.subjectPublicKeyInfo.algorithm.parameters";
+ const char *pk_name = "tbsCertificate.subjectPublicKeyInfo.subjectPublicKey";
+ char algo_oid[MAX_OID_LEN];
+ int algo_size = sizeof (algo_oid);
+ char params_value[2];
+ int params_size = sizeof (params_value);
+ grub_uint8_t *key_data = NULL;
+ int key_size = 0;
+ unsigned int key_type;
+
+ /* algorithm: see notes for rsaEncryption_oid */
+ result = asn1_read_value (asn, algo_name, algo_oid, &algo_size);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading x509 public
key algorithm: %s"),
+ asn1_strerror (result));
+
+ if (grub_strncmp (algo_oid, rsaEncryption_oid, sizeof (rsaEncryption_oid))
!= 0)
+ return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
+ N_("unsupported x509 public key algorithm: %s"),
algo_oid);
+
+ /*
+ * RFC 3279 2.3.1
+ * The rsaEncryption OID is intended to be used in the algorithm field
+ * of a value of type AlgorithmIdentifier. The parameters field MUST
+ * have ASN.1 type NULL for this algorithm identifier.
+ */
+ result = asn1_read_value (asn, params_name, params_value, ¶ms_size);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading x509 public
key parameters: %s"),
+ asn1_strerror (result));
+
+ if (params_value[0] != ASN1_TAG_NULL)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ "invalid x509 public key parameters: expected NULL");
+
+ /*
+ * RFC 3279 2.3.1: The DER encoded RSAPublicKey is the value of the BIT
+ * STRING subjectPublicKey.
+ */
+ result = asn1_read_value_type (asn, pk_name, NULL, &key_size, &key_type);
+ if (result != ASN1_MEM_ERROR)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading size of x509
public key: %s"),
+ asn1_strerror (result));
+ if (key_type != ASN1_ETYPE_BIT_STRING)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("unexpected ASN.1 type when
reading x509 public key: %x"),
+ key_type);
+
+ /* length is in bits */
+ key_size = (key_size + 7) / 8;
+
+ key_data = grub_malloc (key_size);
+ if (key_data == NULL)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY, "out of memory for x509 public
key");
+
+ result = asn1_read_value (asn, pk_name, key_data, &key_size);
+ if (result != ASN1_SUCCESS)
+ {
+ grub_free (key_data);
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, "error reading public key
data");
+ }
+
+ key_size = (key_size + 7) / 8;
+ err = grub_parse_rsa_pubkey (key_data, key_size, results);
+ grub_free (key_data);
+
+ return err;
+}
+
+/* Decode a string as defined in Appendix A */
+static grub_err_t
+decode_string (char *der, int der_size, char **string, grub_size_t
*string_size)
+{
+ asn1_node strasn;
+ int result;
+ char *choice;
+ int choice_size = 0;
+ int tmp_size = 0;
+ grub_err_t err = GRUB_ERR_NONE;
+
+ result = asn1_create_element (grub_gnutls_pkix_asn, "PKIX1.DirectoryString",
&strasn);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not create ASN.1 structure for certificate:
%s"),
+ asn1_strerror (result));
+
+ result = asn1_der_decoding2 (&strasn, der, &der_size,
ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("could not parse DER for DirectoryString: %s"),
asn1_error);
+ goto cleanup;
+ }
+
+ choice = grub_asn1_allocate_and_read (strasn, "", "DirectoryString choice",
&choice_size);
+ if (choice == NULL)
+ {
+ err = grub_errno;
+ goto cleanup;
+ }
+
+ if (grub_strncmp ("utf8String", choice, choice_size) == 0)
+ {
+ result = asn1_read_value (strasn, "utf8String", NULL, &tmp_size);
+ if (result != ASN1_MEM_ERROR)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading size of
UTF-8 string: %s"),
+ asn1_strerror (result));
+ goto cleanup_choice;
+ }
+ }
+ else if (grub_strncmp ("printableString", choice, choice_size) == 0)
+ {
+ result = asn1_read_value (strasn, "printableString", NULL, &tmp_size);
+ if (result != ASN1_MEM_ERROR)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading size of
UTF-8 string: %s"),
+ asn1_strerror (result));
+ goto cleanup_choice;
+ }
+ }
+ else
+ {
+ err = grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
+ N_("only UTF-8 and printable DirectoryStrings are
supported, got %s"),
+ choice);
+ goto cleanup_choice;
+ }
+
+ /* read size does not include trailing null */
+ tmp_size++;
+
+ *string = grub_malloc (tmp_size);
+ if (*string == NULL)
+ {
+ err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ "cannot allocate memory for DirectoryString contents");
+ goto cleanup_choice;
+ }
+
+ result = asn1_read_value (strasn, choice, *string, &tmp_size);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading out %s in
DirectoryString: %s"),
+ choice, asn1_strerror (result));
+ grub_free (*string);
+ *string = NULL;
+ goto cleanup_choice;
+ }
+
+ *string_size = tmp_size + 1;
+ (*string)[tmp_size] = '\0';
+
+ cleanup_choice:
+ grub_free (choice);
+ cleanup:
+ asn1_delete_structure (&strasn);
+
+ return err;
+}
+
+/*
+ * TBSCertificate ::= SEQUENCE {
+ * version [0] EXPLICIT Version DEFAULT v1,
+ * ...
+ *
+ * Version ::= INTEGER { v1(0), v2(1), v3(2) }
+ */
+static grub_err_t
+check_version (asn1_node certificate)
+{
+ int rc;
+ const char *name = "tbsCertificate.version";
+ grub_uint8_t version;
+ int len = sizeof (version);
+
+ rc = asn1_read_value (certificate, name, &version, &len);
+
+ /* require version 3 */
+ if (rc != ASN1_SUCCESS || len != 1)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading certificate
version"));
+
+ if (version != 0x02)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("invalid x509 certificate version, expected v3
(0x02), got 0x%02x"),
+ version);
+
+ return GRUB_ERR_NONE;
+}
+
+/*
+ * This is an X.501 Name, which is complex.
+ *
+ * For simplicity, we extract only the CN.
+ */
+static grub_err_t
+read_name (asn1_node asn, const char *name_path, char **name, grub_size_t
*name_size)
+{
+ int seq_components, set_components;
+ int result;
+ int i, j;
+ char *top_path, *set_path, *type_path, *val_path;
+ char type[MAX_OID_LEN];
+ int type_len = sizeof (type);
+ int string_size = 0;
+ char *string_der;
+ grub_err_t err;
+
+ *name = NULL;
+
+ top_path = grub_xasprintf ("%s.rdnSequence", name_path);
+ if (top_path == NULL)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not allocate memory for %s name parsing
path"), name_path);
+
+ result = asn1_number_of_elements (asn, top_path, &seq_components);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error counting name
components: %s"),
+ asn1_strerror (result));
+ goto cleanup;
+ }
+
+ for (i = 1; i <= seq_components; i++)
+ {
+ set_path = grub_xasprintf ("%s.?%d", top_path, i);
+ if (set_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not allocate memory for %s name set
parsing path"),
+ name_path);
+ goto cleanup_set;
+ }
+ /* this brings us, hopefully, to a set */
+ result = asn1_number_of_elements (asn, set_path, &set_components);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error counting name sub-components components
(element %d): %s"),
+ i, asn1_strerror (result));
+ goto cleanup_set;
+ }
+ for (j = 1; j <= set_components; j++)
+ {
+ type_path = grub_xasprintf ("%s.?%d.?%d.type", top_path, i, j);
+ if (type_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not allocate memory for %s name
component type path"),
+ name_path);
+ goto cleanup_set;
+ }
+ type_len = sizeof (type);
+ result = asn1_read_value (asn, type_path, type, &type_len);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading %s
name component type: %s"),
+ name_path, asn1_strerror (result));
+ goto cleanup_type;
+ }
+
+ if (grub_strncmp (type, commonName_oid, type_len) != 0)
+ {
+ grub_free (type_path);
+ continue;
+ }
+
+ val_path = grub_xasprintf ("%s.?%d.?%d.value", top_path, i, j);
+ if (val_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not allocate memory for %s name
component value path"),
+ name_path);
+ goto cleanup_type;
+ }
+
+ string_der = grub_asn1_allocate_and_read (asn, val_path, name_path,
&string_size);
+ if (string_der == NULL)
+ {
+ err = grub_errno;
+ goto cleanup_val_path;
+ }
+
+ err = decode_string (string_der, string_size, name, name_size);
+ if (err)
+ goto cleanup_string;
+
+ grub_free (string_der);
+ grub_free (type_path);
+ grub_free (val_path);
+ break;
+ }
+
+ grub_free (set_path);
+ if (*name)
+ break;
+ }
+
+ grub_free (top_path);
+
+ return GRUB_ERR_NONE;
+
+ cleanup_string:
+ grub_free (string_der);
+ cleanup_val_path:
+ grub_free (val_path);
+ cleanup_type:
+ grub_free (type_path);
+ cleanup_set:
+ grub_free (set_path);
+ cleanup:
+ grub_free (top_path);
+
+ return err;
+}
+
+/*
+ * Verify the Key Usage extension.
+ * We require the Digital Signature usage.
+ */
+static grub_err_t
+verify_key_usage (grub_uint8_t *value, int value_size)
+{
+ asn1_node usageasn;
+ int result;
+ grub_err_t err = GRUB_ERR_NONE;
+ grub_uint8_t usage = 0xff;
+ int usage_size = sizeof (usage_size);
+
+ result = asn1_create_element (grub_gnutls_pkix_asn, "PKIX1.KeyUsage",
&usageasn);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ "could not create ASN.1 structure for key usage");
+
+ result = asn1_der_decoding2 (&usageasn, value, &value_size,
+ ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error parsing DER for Key Usage: %s"), asn1_error);
+ goto cleanup;
+ }
+
+ result = asn1_read_value (usageasn, "", &usage, &usage_size);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading Key Usage
value: %s"),
+ asn1_strerror (result));
+ goto cleanup;
+ }
+
+ if (!(usage & digitalSignatureUsage))
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("key usage (0x%x) missing Digital Signature
usage"), usage);
+ goto cleanup;
+ }
+
+ cleanup:
+ asn1_delete_structure (&usageasn);
+
+ return err;
+}
+
+/*
+ * BasicConstraints ::= SEQUENCE {
+ * cA BOOLEAN DEFAULT FALSE,
+ * pathLenConstraint INTEGER (0..MAX) OPTIONAL }
+ */
+static grub_err_t
+verify_basic_constraints (grub_uint8_t *value, int value_size)
+{
+ asn1_node basicasn;
+ int result;
+ grub_err_t err = GRUB_ERR_NONE;
+ char cA[6]; /* FALSE or TRUE */
+ int cA_size = sizeof (cA);
+
+ result = asn1_create_element (grub_gnutls_pkix_asn,
"PKIX1.BasicConstraints", &basicasn);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ "could not create ASN.1 structure for Basic
Constraints");
+
+ result = asn1_der_decoding2 (&basicasn, value, &value_size,
+ ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error parsing DER for Basic Constraints: %s"),
asn1_error);
+ goto cleanup;
+ }
+
+ result = asn1_read_value (basicasn, "cA", cA, &cA_size);
+ if (result == ASN1_ELEMENT_NOT_FOUND)
+ {
+ /* Not present, default is False, so this is OK */
+ err = GRUB_ERR_NONE;
+ goto cleanup;
+ }
+ else if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading Basic
Constraints cA value: %s"),
+ asn1_strerror (result));
+ goto cleanup;
+ }
+
+ /* The certificate must not be a CA certificate */
+ if (grub_strncmp ("FALSE", cA, cA_size) != 0)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("unexpected CA value: %s"),
cA);
+ goto cleanup;
+ }
+
+ cleanup:
+ asn1_delete_structure (&basicasn);
+
+ return err;
+}
+
+/*
+ * Verify the Extended Key Usage extension.
+ * We require the Code Signing usage.
+ *
+ * ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
+ *
+ * KeyPurposeId ::= OBJECT IDENTIFIER
+ */
+static grub_err_t
+verify_extended_key_usage (grub_uint8_t *value, int value_size)
+{
+ asn1_node extendedasn;
+ int result, count, i = 0;
+ grub_err_t err = GRUB_ERR_NONE;
+ char usage[MAX_OID_LEN], name[3];
+ int usage_size = sizeof (usage);
+
+ result = asn1_create_element (grub_gnutls_pkix_asn,
"PKIX1.ExtKeyUsageSyntax", &extendedasn);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ "could not create ASN.1 structure for Extended Key
Usage");
+
+ result = asn1_der_decoding2 (&extendedasn, value, &value_size,
+ ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("error parsing DER for Extended Key Usage: %s"),
asn1_error);
+ goto cleanup;
+ }
+
+ /* If EKUs are present, it checks the presents of Code Signing usage */
+ result = asn1_number_of_elements (extendedasn, "", &count);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error counting number of
Extended Key Usages: %s"),
+ asn1_strerror (result));
+ goto cleanup;
+ }
+
+
+ for (i = 1; i < count + 1; i++)
+ {
+ grub_memset (name, 0, sizeof (name));
+ grub_snprintf (name, sizeof (name), "?%d", i);
+ result = asn1_read_value (extendedasn, name, usage, &usage_size);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading Extended
Key Usage: %s"),
+ asn1_strerror (result));
+ goto cleanup;
+ }
+
+ if (grub_strncmp (codeSigningUsage_oid, usage, usage_size) == 0)
+ goto cleanup;
+ }
+
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, "extended key usage missing Code
Signing usage");
+
+ cleanup:
+ asn1_delete_structure (&extendedasn);
+
+ return err;
+}
+
+/*
+ * Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
+ *
+ * Extension ::= SEQUENCE {
+ * extnID OBJECT IDENTIFIER,
+ * critical BOOLEAN DEFAULT FALSE,
+ * extnValue OCTET STRING
+ * -- contains the DER encoding of an ASN.1 value
+ * -- corresponding to the extension type identified
+ * -- by extnID
+ * }
+ *
+ * A certificate must:
+ * - contain the Digital Signature usage
+ * - not be a CA
+ * - contain no extended usages, or contain the Code Signing extended usage
+ * - not contain any other critical extensions (RFC 5280 s 4.2)
+ */
+static grub_err_t
+verify_extensions (asn1_node cert)
+{
+ int result;
+ int ext, num_extensions = 0;
+ int usage_present = 0, constraints_present = 0, extended_usage_present = 0;
+ char *oid_path, *critical_path, *value_path;
+ char extnID[MAX_OID_LEN];
+ int extnID_size;
+ grub_err_t err;
+ char critical[6]; /* we get either "TRUE" or "FALSE" */
+ int critical_size;
+ grub_uint8_t *value;
+ int value_size;
+
+ result = asn1_number_of_elements (cert, "tbsCertificate.extensions",
&num_extensions);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error counting number of
extensions: %s"),
+ asn1_strerror (result));
+
+ if (num_extensions < 2)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("insufficient number of extensions for certificate,
need at least 2, got %d"),
+ num_extensions);
+
+ for (ext = 1; ext <= num_extensions; ext++)
+ {
+ oid_path = grub_xasprintf ("tbsCertificate.extensions.?%d.extnID", ext);
+ if (oid_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, "error extension OID path
is empty");
+ return err;
+ }
+
+ extnID_size = sizeof (extnID);
+ result = asn1_read_value (cert, oid_path, extnID, &extnID_size);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading
extension OID: %s"),
+ asn1_strerror (result));
+ goto cleanup_oid_path;
+ }
+
+ critical_path = grub_xasprintf
("tbsCertificate.extensions.?%d.critical", ext);
+ if (critical_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, "error critical path is
empty");
+ goto cleanup_oid_path;
+ }
+
+ critical_size = sizeof (critical);
+ result = asn1_read_value (cert, critical_path, critical, &critical_size);
+ if (result == ASN1_ELEMENT_NOT_FOUND)
+ critical[0] = '\0';
+ else if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("error reading
extension criticality: %s"),
+ asn1_strerror (result));
+ goto cleanup_critical_path;
+ }
+
+ value_path = grub_xasprintf ("tbsCertificate.extensions.?%d.extnValue",
ext);
+ if (value_path == NULL)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE, "error extnValue path is
empty");
+ goto cleanup_critical_path;
+ }
+
+ value = grub_asn1_allocate_and_read (cert, value_path,
+ "certificate extension value",
&value_size);
+ if (value == NULL)
+ {
+ err = grub_errno;
+ goto cleanup_value_path;
+ }
+
+ /*
+ * Now we must see if we recognise the OID.
+ * If we have an unrecognised critical extension we MUST bail.
+ */
+ if (grub_strncmp (keyUsage_oid, extnID, extnID_size) == 0)
+ {
+ err = verify_key_usage (value, value_size);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_value;
+
+ usage_present++;
+ }
+ else if (grub_strncmp (basicConstraints_oid, extnID, extnID_size) == 0)
+ {
+ err = verify_basic_constraints (value, value_size);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_value;
+
+ constraints_present++;
+ }
+ else if (grub_strncmp (extendedKeyUsage_oid, extnID, extnID_size) == 0)
+ {
+ err = verify_extended_key_usage (value, value_size);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_value;
+
+ extended_usage_present++;
+ }
+ else if (grub_strncmp ("TRUE", critical, critical_size) == 0)
+ {
+ /*
+ * per the RFC, we must not process a certificate with
+ * a critical extension we do not understand.
+ */
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("unhandled critical x509 extension with OID
%s"), extnID);
+ goto cleanup_value;
+ }
+
+ grub_free (value);
+ grub_free (value_path);
+ grub_free (critical_path);
+ grub_free (oid_path);
+ }
+
+ if (usage_present != 1)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("unexpected number of Key Usage extensions -
expected 1, got %d"),
+ usage_present);
+
+ if (constraints_present != 1)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("unexpected number of basic constraints extensions -
expected 1, got %d"),
+ constraints_present);
+
+ if (extended_usage_present > 1)
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("unexpected number of Extended Key Usage extensions
- expected 0 or 1, got %d"),
+ extended_usage_present);
+
+ return GRUB_ERR_NONE;
+
+ cleanup_value:
+ grub_free (value);
+ cleanup_value_path:
+ grub_free (value_path);
+ cleanup_critical_path:
+ grub_free (critical_path);
+ cleanup_oid_path:
+ grub_free (oid_path);
+
+ return err;
+}
+
+/*
+ * Parse a certificate whose DER-encoded form is in @data, of size @data_size.
+ * Return the results in @results, which must point to an allocated x509
certificate.
+ */
+grub_err_t
+parse_x509_certificate (const void *data, grub_size_t data_size, struct
x509_certificate *results)
+{
+ int result = 0;
+ asn1_node cert;
+ grub_err_t err;
+ int size;
+ int tmp_size;
+
+ if (data_size > GRUB_INT_MAX)
+ return grub_error (GRUB_ERR_OUT_OF_RANGE,
+ "cannot parse a certificate where data size > INT_MAX");
+ size = (int) data_size;
+
+ result = asn1_create_element (grub_gnutls_pkix_asn, "PKIX1.Certificate",
&cert);
+ if (result != ASN1_SUCCESS)
+ return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+ N_("could not create ASN.1 structure for certificate:
%s"),
+ asn1_strerror (result));
+
+ result = asn1_der_decoding2 (&cert, data, &size,
ASN1_DECODE_FLAG_STRICT_DER, asn1_error);
+ if (result != ASN1_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ N_("could not parse DER for certificate: %s"),
asn1_error);
+ goto cleanup;
+ }
+
+ /*
+ * TBSCertificate ::= SEQUENCE {
+ * version [0] EXPLICIT Version DEFAULT v1
+ */
+ err = check_version (cert);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup;
+
+ /*
+ * serialNumber CertificateSerialNumber,
+ *
+ * CertificateSerialNumber ::= INTEGER
+ */
+ results->serial = grub_asn1_allocate_and_read (cert,
"tbsCertificate.serialNumber",
+ "certificate serial number",
&tmp_size);
+ if (results->serial == NULL)
+ {
+ err = grub_errno;
+ goto cleanup;
+ }
+ /*
+ * It's safe to cast the signed int to an unsigned here, we know
+ * length is non-negative
+ */
+ results->serial_len = tmp_size;
+
+ /*
+ * signature AlgorithmIdentifier,
+ *
+ * We don't load the signature or issuer at the moment,
+ * as we don't attempt x509 verification.
+ */
+
+ /*
+ * issuer Name,
+ *
+ * The RFC only requires the serial number to be unique within
+ * issuers, so to avoid ambiguity we _technically_ ought to make
+ * this available.
+ */
+
+ /*
+ * validity Validity,
+ *
+ * Validity ::= SEQUENCE {
+ * notBefore Time,
+ * notAfter Time }
+ *
+ * We can't validate this reasonably, we have no true time source on several
+ * platforms. For now we do not parse them.
+ */
+
+ /*
+ * subject Name,
+ *
+ * This is an X501 name, we parse out just the CN.
+ */
+ err = read_name (cert, "tbsCertificate.subject", &results->subject,
&results->subject_len);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_serial;
+
+ /*
+ * TBSCertificate ::= SEQUENCE {
+ * ...
+ * subjectPublicKeyInfo SubjectPublicKeyInfo,
+ * ...
+ */
+ err = grub_x509_read_subject_public_key (cert, results);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_name;
+
+ /*
+ * TBSCertificate ::= SEQUENCE {
+ * ...
+ * extensions [3] EXPLICIT Extensions OPTIONAL
+ * -- If present, version MUST be v3
+ * }
+ */
+ err = verify_extensions (cert);
+ if (err != GRUB_ERR_NONE)
+ goto cleanup_mpis;
+
+ /*
+ * We do not read or check the signature on the certificate:
+ * as discussed we do not try to validate the certificate but trust
+ * it implictly.
+ */
+ asn1_delete_structure (&cert);
+
+ return GRUB_ERR_NONE;
+
+ cleanup_mpis:
+ gcry_mpi_release (results->mpis[0]);
+ gcry_mpi_release (results->mpis[1]);
+ cleanup_name:
+ grub_free (results->subject);
+ cleanup_serial:
+ grub_free (results->serial);
+ cleanup:
+ asn1_delete_structure (&cert);
+
+ return err;
+}
+
+/*
+ * Release all the storage associated with the x509 certificate.
+ * If the caller dynamically allocated the certificate, it must free it.
+ * The caller is also responsible for maintenance of the linked list.
+ */
+void
+certificate_release (struct x509_certificate *cert)
+{
+ grub_free (cert->subject);
+ grub_free (cert->serial);
+ gcry_mpi_release (cert->mpis[0]);
+ gcry_mpi_release (cert->mpis[1]);
+}
--
2.49.0
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