Improve client certificate selection for TLSv1.3

This allows clients to use EC certificates.

ok inoguchi, jsing

1 files changed, 80 insertions, 16 deletions

diff --git a/src/lib/libssl/tls13_client.c b/src/lib/libssl/tls13_client.c
index d7a912a7e1..e2f61f6c08 100644
--- a/src/lib/libssl/tls13_client.c
+++ b/src/lib/libssl/tls13_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_client.c,v 1.64 2020/05/23 11:58:46 jsing Exp $ */
+/* $OpenBSD: tls13_client.c,v 1.65 2020/06/04 18:41:42 tb Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -826,30 +826,98 @@ tls13_server_finished_recv(struct tls13_ctx *ctx, CBS *cbs)
         return ret;
 }
 
+static int
+tls13_client_check_certificate(struct tls13_ctx *ctx, CERT_PKEY *cpk,
+    int *ok, const struct ssl_sigalg **out_sigalg)
+{
+        const struct ssl_sigalg *sigalg;
+        SSL *s = ctx->ssl;
+
+        *ok = 0;
+        *out_sigalg = NULL;
+
+        if (cpk->x509 == NULL || cpk->privatekey == NULL)
+                goto done;
+
+        if ((sigalg = ssl_sigalg_select(s, cpk->privatekey)) == NULL)
+                goto done;
+
+        *ok = 1;
+        *out_sigalg = sigalg;
+
+ done:
+        return 1;
+}
+
+static int
+tls13_client_select_certificate(struct tls13_ctx *ctx, CERT_PKEY **out_cpk,
+    const struct ssl_sigalg **out_sigalg)
+{
+        SSL *s = ctx->ssl;
+        const struct ssl_sigalg *sigalg;
+        CERT_PKEY *cpk;
+        int cert_ok;
+
+        *out_cpk = NULL;
+        *out_sigalg = NULL;
+
+        /*
+         * XXX - RFC 8446, 4.4.2.3: the server can communicate preferences
+         * with the certificate_authorities (4.2.4) and oid_filters (4.2.5)
+         * extensions. We should honor the former and must apply the latter.
+         */
+
+        cpk = &s->cert->pkeys[SSL_PKEY_ECC];
+        if (!tls13_client_check_certificate(ctx, cpk, &cert_ok, &sigalg))
+                return 0;
+        if (cert_ok)
+                goto done;
+
+        cpk = &s->cert->pkeys[SSL_PKEY_RSA];
+        if (!tls13_client_check_certificate(ctx, cpk, &cert_ok, &sigalg))
+                return 0;
+        if (cert_ok)
+                goto done;
+
+        cpk = NULL;
+        sigalg = NULL;
+
+ done:
+        *out_cpk = cpk;
+        *out_sigalg = sigalg;
+
+        return 1;
+}
+
 int
 tls13_client_certificate_send(struct tls13_ctx *ctx, CBB *cbb)
 {
         SSL *s = ctx->ssl;
         CBB cert_request_context, cert_list;
+        const struct ssl_sigalg *sigalg;
         STACK_OF(X509) *chain;
         CERT_PKEY *cpk;
         X509 *cert;
         int i, ret = 0;
 
-        /* XXX - Need to revisit certificate selection. */
-        cpk = &s->cert->pkeys[SSL_PKEY_RSA];
+        if (!tls13_client_select_certificate(ctx, &cpk, &sigalg))
+                goto err;
 
-        if ((chain = cpk->chain) == NULL)
-                chain = s->ctx->extra_certs;
+        ctx->hs->cpk = cpk;
+        ctx->hs->sigalg = sigalg;
 
         if (!CBB_add_u8_length_prefixed(cbb, &cert_request_context))
                 goto err;
         if (!CBB_add_u24_length_prefixed(cbb, &cert_list))
                 goto err;
 
-        if (cpk->x509 == NULL)
+        /* No certificate selected. */
+        if (cpk == NULL)
                 goto done;
 
+        if ((chain = cpk->chain) == NULL)
+               chain = s->ctx->extra_certs;
+
         if (!tls13_cert_add(ctx, &cert_list, cpk->x509, tlsext_client_build))
                 goto err;
 
@@ -873,27 +941,23 @@ tls13_client_certificate_send(struct tls13_ctx *ctx, CBB *cbb)
 int
 tls13_client_certificate_verify_send(struct tls13_ctx *ctx, CBB *cbb)
 {
-        SSL *s = ctx->ssl;
-        const struct ssl_sigalg *sigalg = NULL;
+        const struct ssl_sigalg *sigalg;
         uint8_t *sig = NULL, *sig_content = NULL;
         size_t sig_len, sig_content_len;
         EVP_MD_CTX *mdctx = NULL;
         EVP_PKEY_CTX *pctx;
         EVP_PKEY *pkey;
-        CERT_PKEY *cpk;
+        const CERT_PKEY *cpk;
         CBB sig_cbb;
         int ret = 0;
 
         memset(&sig_cbb, 0, sizeof(sig_cbb));
 
-        /* XXX - Need to revisit certificate selection. */
-        cpk = &s->cert->pkeys[SSL_PKEY_RSA];
-        pkey = cpk->privatekey;
-
-        if ((sigalg = ssl_sigalg_select(s, pkey)) == NULL) {
-                /* XXX - SSL_R_SIGNATURE_ALGORITHMS_ERROR */
+        if ((cpk = ctx->hs->cpk) == NULL)
                 goto err;
-        }
+        if ((sigalg = ctx->hs->sigalg) == NULL)
+                goto err;
+        pkey = cpk->privatekey;
 
         if (!CBB_init(&sig_cbb, 0))
                 goto err;