Add functions that check security level in certs and cert chains.

ok beck jsing

2 files changed, 147 insertions, 2 deletions

diff --git a/src/lib/libssl/ssl_locl.h b/src/lib/libssl/ssl_locl.h
index d979baf301..161a8407af 100644
--- a/src/lib/libssl/ssl_locl.h
+++ b/src/lib/libssl/ssl_locl.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_locl.h,v 1.403 2022/06/29 20:04:28 tb Exp $ */
+/* $OpenBSD: ssl_locl.h,v 1.404 2022/06/29 21:10:20 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1300,6 +1300,10 @@ int ssl_ctx_security(const SSL_CTX *ctx, int op, int bits, int nid,
 int ssl_security(const SSL *ssl, int op, int bits, int nid, void *other);
 int ssl_ctx_security_dh(const SSL_CTX *ctx, DH *dh);
 int ssl_security_dh(const SSL *ssl, DH *dh);
+int ssl_security_cert(const SSL_CTX *ctx, const SSL *ssl, X509 *x509,
+    int is_peer, int *out_error);
+int ssl_security_cert_chain(const SSL *ssl, STACK_OF(X509) *sk,
+    X509 *x509, int *out_error);
 
 int ssl_get_new_session(SSL *s, int session);
 int ssl_get_prev_session(SSL *s, CBS *session_id, CBS *ext_block,
diff --git a/src/lib/libssl/ssl_seclevel.c b/src/lib/libssl/ssl_seclevel.c
index 1db2a2dbcd..b24999498c 100644
--- a/src/lib/libssl/ssl_seclevel.c
+++ b/src/lib/libssl/ssl_seclevel.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: ssl_seclevel.c,v 1.8 2022/06/29 11:59:23 tb Exp $ */
+/*      $OpenBSD: ssl_seclevel.c,v 1.9 2022/06/29 21:10:20 tb Exp $ */
 /*
  * Copyright (c) 2020 Theo Buehler <tb@openbsd.org>
  *
@@ -17,10 +17,15 @@
 
 #include <stddef.h>
 
+#include <openssl/asn1.h>
 #include <openssl/dh.h>
+#include <openssl/evp.h>
+#include <openssl/obj_mac.h>
+#include <openssl/objects.h>
 #include <openssl/ossl_typ.h>
 #include <openssl/ssl.h>
 #include <openssl/tls1.h>
+#include <openssl/x509.h>
 
 #include "ssl_locl.h"
 
@@ -247,3 +252,139 @@ ssl_security_dh(const SSL *ssl, DH *dh)
         return 1;
 #endif
 }
+
+#if defined(LIBRESSL_HAS_SECURITY_LEVEL)
+static int
+ssl_cert_pubkey_security_bits(const X509 *x509)
+{
+        EVP_PKEY *pkey;
+
+        if ((pkey = X509_get0_pubkey(x509)) == NULL)
+                return -1;
+
+        /*
+         * XXX: DSA_security_bits() returns -1 on keys without parameters and
+         * cause the default security callback to fail.
+         */
+
+        return EVP_PKEY_security_bits(pkey);
+}
+
+static int
+ssl_security_cert_key(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int op)
+{
+        int security_bits;
+
+        security_bits = ssl_cert_pubkey_security_bits(x509);
+
+        if (ssl != NULL)
+                return ssl_security(ssl, op, security_bits, 0, x509);
+
+        return ssl_ctx_security(ctx, op, security_bits, 0, x509);
+}
+
+static int
+ssl_cert_signature_md_nid(const X509 *x509)
+{
+        int md_nid, signature_nid;
+
+        if ((signature_nid = X509_get_signature_nid(x509)) == NID_undef)
+                return NID_undef;
+
+        if (!OBJ_find_sigid_algs(signature_nid, &md_nid, NULL))
+                return NID_undef;
+
+        return md_nid;
+}
+
+static int
+ssl_cert_md_nid_security_bits(int md_nid)
+{
+        const EVP_MD *md;
+
+        if (md_nid == NID_undef)
+                return -1;
+
+        if ((md = EVP_get_digestbynid(md_nid)) == NULL)
+                return -1;
+
+        /* Assume 4 bits of collision resistance for each hash octet. */
+        return EVP_MD_size(md) * 4;
+}
+
+static int
+ssl_security_cert_sig(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int op)
+{
+        int md_nid, security_bits;
+
+        md_nid = ssl_cert_signature_md_nid(x509);
+        security_bits = ssl_cert_md_nid_security_bits(md_nid);
+
+        if (ssl != NULL)
+                return ssl_security(ssl, op, security_bits, md_nid, x509);
+
+        return ssl_ctx_security(ctx, op, security_bits, md_nid, x509);
+}
+#endif
+
+int
+ssl_security_cert(const SSL_CTX *ctx, const SSL *ssl, X509 *x509,
+    int is_ee, int *out_error)
+{
+#if defined(LIBRESSL_HAS_SECURITY_LEVEL)
+        int key_error, operation;
+
+        *out_error = 0;
+
+        if (is_ee) {
+                operation = SSL_SECOP_EE_KEY;
+                key_error = SSL_R_EE_KEY_TOO_SMALL;
+        } else {
+                operation = SSL_SECOP_CA_KEY;
+                key_error = SSL_R_CA_KEY_TOO_SMALL;
+        }
+
+        if (!ssl_security_cert_key(ctx, ssl, x509, operation)) {
+                *out_error = key_error;
+                return 0;
+        }
+
+        if (!ssl_security_cert_sig(ctx, ssl, x509, SSL_SECOP_CA_MD)) {
+                *out_error = SSL_R_CA_MD_TOO_WEAK;
+                return 0;
+        }
+
+#endif
+        return 1;
+}
+
+/*
+ * Check security of a chain. If |sk| includes the end entity certificate
+ * then |x509| must be NULL.
+ */
+int
+ssl_security_cert_chain(const SSL *ssl, STACK_OF(X509) *sk, X509 *x509,
+    int *out_error)
+{
+        int start_idx = 0;
+        int is_ee;
+        int i;
+
+        if (x509 == NULL) {
+                x509 = sk_X509_value(sk, 0);
+                start_idx = 1;
+        }
+
+        if (!ssl_security_cert(NULL, ssl, x509, is_ee = 1, out_error))
+                return 0;
+
+        for (i = start_idx; i < sk_X509_num(sk); i++) {
+                x509 = sk_X509_value(sk, i);
+
+                if (!ssl_security_cert(NULL, ssl, x509, is_ee = 0,
+                    out_error))
+                        return 0;
+        }
+
+        return 1;
+}