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[crypto] Do not allow build-time cryptography settings to be overridden
If a root certificate has been explicitly specified at build time using TRUST=/path/to/cert then do not allow this to be overridden even from a trustworthy settings source (such as VMware GuestInfo). Similarly, if a client certificate (and private key) has been explicitly specified at build time, then do not allow it to be overridden at runtime. Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
parent
63d9cc28b9
commit
bd16deaa87
@ -47,6 +47,13 @@ FILE_LICENCE ( GPL2_OR_LATER );
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#warning "Attempting to embed private key with no corresponding certificate"
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#endif
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/* Allow client certificates to be overridden if not explicitly specified */
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#ifdef CERTIFICATE
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#define ALLOW_CERT_OVERRIDE 0
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#else
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#define ALLOW_CERT_OVERRIDE 1
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#endif
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/* Raw client certificate data */
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extern char client_certificate_data[];
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extern char client_certificate_len[];
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@ -72,13 +79,19 @@ __asm__ ( ".section \".rodata\", \"a\", @progbits\n\t"
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".previous\n\t" );
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/** Client certificate */
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struct client_certificate client_certificate;
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struct client_certificate client_certificate = {
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.data = client_certificate_data,
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.len = ( ( size_t ) client_certificate_len ),
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};
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/** Client private key */
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struct client_private_key client_private_key;
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struct client_private_key client_private_key = {
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.data = client_private_key_data,
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.len = ( ( size_t ) client_private_key_len ),
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};
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/** Client certificate setting */
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struct setting cert_setting __setting ( SETTING_CRYPTO ) = {
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static struct setting cert_setting __setting ( SETTING_CRYPTO ) = {
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.name = "cert",
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.description = "Client certificate",
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.tag = DHCP_EB_CERT,
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@ -86,7 +99,7 @@ struct setting cert_setting __setting ( SETTING_CRYPTO ) = {
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};
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/** Client private key setting */
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struct setting key_setting __setting ( SETTING_CRYPTO ) = {
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static struct setting key_setting __setting ( SETTING_CRYPTO ) = {
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.name = "key",
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.description = "Client private key",
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.tag = DHCP_EB_KEY,
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@ -99,45 +112,51 @@ struct setting key_setting __setting ( SETTING_CRYPTO ) = {
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* @ret rc Return status code
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*/
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static int clientcert_apply_settings ( void ) {
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static void *cert;
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static void *key;
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static void *cert = NULL;
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static void *key = NULL;
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int len;
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int rc;
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/* Restore default client certificate */
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client_certificate.data = client_certificate_data;
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client_certificate.len = ( ( size_t ) client_certificate_len );
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/* Allow client certificate to be overridden only if
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* not explicitly specified at build time.
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*/
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if ( ALLOW_CERT_OVERRIDE ) {
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/* Fetch new client certificate, if any */
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free ( cert );
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len = fetch_setting_copy ( NULL, &cert_setting, &cert );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &client_certificate, "CLIENTCERT cannot fetch client "
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"certificate: %s\n", strerror ( rc ) );
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return rc;
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}
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if ( cert ) {
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client_certificate.data = cert;
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client_certificate.len = len;
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}
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/* Restore default client certificate */
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client_certificate.data = client_certificate_data;
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client_certificate.len = ( ( size_t ) client_certificate_len );
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/* Restore default client private key */
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client_private_key.data = client_private_key_data;
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client_private_key.len = ( ( size_t ) client_private_key_len );
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/* Fetch new client certificate, if any */
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free ( cert );
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len = fetch_setting_copy ( NULL, &cert_setting, &cert );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &client_certificate, "CLIENTCERT cannot fetch "
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"client certificate: %s\n", strerror ( rc ) );
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return rc;
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}
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if ( cert ) {
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client_certificate.data = cert;
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client_certificate.len = len;
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}
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/* Fetch new client private key, if any */
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free ( key );
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len = fetch_setting_copy ( NULL, &key_setting, &key );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &client_certificate, "CLIENTCERT cannot fetch client "
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"private key: %s\n", strerror ( rc ) );
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return rc;
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}
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if ( key ) {
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client_private_key.data = key;
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client_private_key.len = len;
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/* Restore default client private key */
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client_private_key.data = client_private_key_data;
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client_private_key.len = ( ( size_t ) client_private_key_len );
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/* Fetch new client private key, if any */
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free ( key );
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len = fetch_setting_copy ( NULL, &key_setting, &key );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &client_certificate, "CLIENTCERT cannot fetch "
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"client private key: %s\n", strerror ( rc ) );
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return rc;
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}
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if ( key ) {
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client_private_key.data = key;
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client_private_key.len = len;
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}
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}
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/* Debug */
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@ -36,6 +36,13 @@ FILE_LICENCE ( GPL2_OR_LATER );
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/** Length of a root certificate fingerprint */
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#define FINGERPRINT_LEN SHA256_DIGEST_SIZE
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/* Allow trusted certificates to be overridden if not explicitly specified */
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#ifdef TRUSTED
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#define ALLOW_TRUST_OVERRIDE 0
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#else
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#define ALLOW_TRUST_OVERRIDE 1
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#endif
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/* Use iPXE root CA if no trusted certificates are explicitly specified */
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#ifndef TRUSTED
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#define TRUSTED \
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@ -50,9 +57,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
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static const uint8_t fingerprints[] = { TRUSTED };
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/** Root certificate fingerprint setting */
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struct setting trust_setting __setting ( SETTING_CRYPTO ) = {
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static struct setting trust_setting __setting ( SETTING_CRYPTO ) = {
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.name = "trust",
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.description = "Trusted root certificate fingerprint",
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.description = "Trusted root certificate fingerprints",
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.tag = DHCP_EB_TRUST,
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.type = &setting_type_hex,
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};
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@ -67,38 +74,50 @@ struct x509_root root_certificates = {
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/**
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* Initialise root certificate
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*
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* We allow the list of trusted root certificate fingerprints to be
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* overridden using the "trust" setting, but only at the point of iPXE
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* The list of trusted root certificates can be specified at build
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* time using the TRUST= build parameter. If no certificates are
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* specified, then the default iPXE root CA certificate is trusted.
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*
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* If no certificates were explicitly specified, then we allow the
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* list of trusted root certificate fingerprints to be overridden
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* using the "trust" setting, but only at the point of iPXE
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* initialisation. This prevents untrusted sources of settings
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* (e.g. DHCP) from subverting the chain of trust, while allowing
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* trustworthy sources (e.g. VMware GuestInfo or non-volatile stored
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* options) to change the trusted root certificate without requiring a
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* rebuild.
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* options) to specify the trusted root certificate without requiring
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* a rebuild.
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*/
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static void rootcert_init ( void ) {
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void *external;
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void *external = NULL;
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int len;
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int rc;
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/* Fetch copy of "trust" setting, if it exists. This memory
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* will never be freed.
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/* Allow trusted root certificates to be overridden only if
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* not explicitly specified at build time.
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*/
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len = fetch_setting_copy ( NULL, &trust_setting, &external );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &root_certificates, "ROOTCERT cannot fetch trusted "
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"root certificate fingerprints: %s\n", strerror ( rc ) );
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/* No way to prevent startup; fail safe by trusting no
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* certificates.
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*/
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root_certificates.count = 0;
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return;
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}
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if ( ALLOW_TRUST_OVERRIDE ) {
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/* Use certificates from "trust" setting, if present */
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if ( external ) {
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root_certificates.fingerprints = external;
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root_certificates.count = ( len / FINGERPRINT_LEN );
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/* Fetch copy of "trust" setting, if it exists. This
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* memory will never be freed.
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*/
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len = fetch_setting_copy ( NULL, &trust_setting, &external );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &root_certificates, "ROOTCERT cannot fetch "
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"trusted root certificate fingerprints: %s\n",
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strerror ( rc ) );
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/* No way to prevent startup; fail safe by
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* trusting no certificates.
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*/
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root_certificates.count = 0;
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return;
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}
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/* Use certificates from "trust" setting, if present */
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if ( external ) {
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root_certificates.fingerprints = external;
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root_certificates.count = ( len / FINGERPRINT_LEN );
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}
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}
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DBGC ( &root_certificates, "ROOTCERT using %d %s certificate(s):\n",
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