Factor out certificate list parsing.

This is already duplicated between client and server and otherwise will
get duplicated yet again for TLS 1.3.

Change-Id: Ia8a352f9bc76fab0f88c1629d08a1da4c13d2510
Reviewed-on: https://boringssl-review.googlesource.com/8778
Reviewed-by: David Benjamin <davidben@google.com>

4 files changed, 116 insertions, 142 deletions

diff --git a/ssl/handshake_client.c b/ssl/handshake_client.c
index a110aeae..267e164d 100644
--- a/ssl/handshake_client.c
+++ b/ssl/handshake_client.c
@@ -966,91 +966,48 @@ err:
 }
 
 static int ssl3_get_server_certificate(SSL *ssl) {
-  int al, ret = -1;
-  X509 *x = NULL;
-  STACK_OF(X509) *sk = NULL;
-  EVP_PKEY *pkey = NULL;
-  CBS cbs, certificate_list;
-  const uint8_t *data;
-
-  int msg_ret =
+  int ret =
       ssl->method->ssl_get_message(ssl, SSL3_MT_CERTIFICATE, ssl_hash_message);
-  if (msg_ret <= 0) {
-    return msg_ret;
+  if (ret <= 0) {
+    return ret;
   }
 
+  CBS cbs;
   CBS_init(&cbs, ssl->init_msg, ssl->init_num);
-
-  sk = sk_X509_new_null();
-  if (sk == NULL) {
-    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
+  uint8_t alert;
+  STACK_OF(X509) *chain = ssl_parse_cert_chain(ssl, &alert, NULL, &cbs);
+  if (chain == NULL) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
     goto err;
   }
 
-  if (!CBS_get_u24_length_prefixed(&cbs, &certificate_list) ||
-      CBS_len(&certificate_list) == 0 ||
-      CBS_len(&cbs) != 0) {
-    al = SSL_AD_DECODE_ERROR;
+  if (sk_X509_num(chain) == 0 || CBS_len(&cbs) != 0) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
-    goto f_err;
-  }
-
-  while (CBS_len(&certificate_list) > 0) {
-    CBS certificate;
-    if (!CBS_get_u24_length_prefixed(&certificate_list, &certificate)) {
-      al = SSL_AD_DECODE_ERROR;
-      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_LENGTH_MISMATCH);
-      goto f_err;
-    }
-    /* A u24 length cannot overflow a long. */
-    data = CBS_data(&certificate);
-    x = d2i_X509(NULL, &data, (long)CBS_len(&certificate));
-    if (x == NULL) {
-      al = SSL_AD_BAD_CERTIFICATE;
-      OPENSSL_PUT_ERROR(SSL, ERR_R_ASN1_LIB);
-      goto f_err;
-    }
-    if (data != CBS_data(&certificate) + CBS_len(&certificate)) {
-      al = SSL_AD_DECODE_ERROR;
-      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_LENGTH_MISMATCH);
-      goto f_err;
-    }
-    if (!sk_X509_push(sk, x)) {
-      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
-      goto err;
-    }
-    x = NULL;
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    goto err;
   }
 
-  X509 *leaf = sk_X509_value(sk, 0);
+  X509 *leaf = sk_X509_value(chain, 0);
   if (!ssl3_check_leaf_certificate(ssl, leaf)) {
-    al = SSL_AD_ILLEGAL_PARAMETER;
-    goto f_err;
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+    goto err;
   }
 
   /* NOTE: Unlike the server half, the client's copy of |cert_chain| includes
    * the leaf. */
   sk_X509_pop_free(ssl->session->cert_chain, X509_free);
-  ssl->session->cert_chain = sk;
-  sk = NULL;
+  ssl->session->cert_chain = chain;
 
   X509_free(ssl->session->peer);
   ssl->session->peer = X509_up_ref(leaf);
 
   ssl->session->verify_result = ssl->verify_result;
 
-  ret = 1;
-
-  if (0) {
-  f_err:
-    ssl3_send_alert(ssl, SSL3_AL_FATAL, al);
-  }
+  return 1;
 
 err:
-  EVP_PKEY_free(pkey);
-  X509_free(x);
-  sk_X509_pop_free(sk, X509_free);
-  return ret;
+  sk_X509_pop_free(chain, X509_free);
+  return -1;
 }
 
 static int ssl3_get_cert_status(SSL *ssl) {
diff --git a/ssl/handshake_server.c b/ssl/handshake_server.c
index c041bb82..96b86238 100644
--- a/ssl/handshake_server.c
+++ b/ssl/handshake_server.c
@@ -165,7 +165,6 @@
 #include <openssl/mem.h>
 #include <openssl/nid.h>
 #include <openssl/rand.h>
-#include <openssl/sha.h>
 #include <openssl/x509.h>
 
 #include "internal.h"
@@ -1247,13 +1246,6 @@ static int ssl3_send_server_hello_done(SSL *ssl) {
 }
 
 static int ssl3_get_client_certificate(SSL *ssl) {
-  int al, ret = -1;
-  X509 *x = NULL;
-  STACK_OF(X509) *sk = NULL;
-  SHA256_CTX sha256;
-  CBS certificate_msg, certificate_list;
-  int is_first_certificate = 1;
-
   assert(ssl->s3->tmp.cert_request);
 
   int msg_ret = ssl->method->ssl_get_message(ssl, -1, ssl_hash_message);
@@ -1268,120 +1260,82 @@ static int ssl3_get_client_certificate(SSL *ssl) {
       if ((ssl->verify_mode & SSL_VERIFY_PEER) &&
           (ssl->verify_mode & SSL_VERIFY_FAIL_IF_NO_PEER_CERT)) {
         OPENSSL_PUT_ERROR(SSL, SSL_R_PEER_DID_NOT_RETURN_A_CERTIFICATE);
-        al = SSL_AD_HANDSHAKE_FAILURE;
-        goto f_err;
+        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+        return -1;
       }
 
       ssl->s3->tmp.reuse_message = 1;
       return 1;
     }
 
-    al = SSL_AD_UNEXPECTED_MESSAGE;
     OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_MESSAGE);
-    goto f_err;
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
+    return -1;
   }
 
+  CBS certificate_msg;
   CBS_init(&certificate_msg, ssl->init_msg, ssl->init_num);
-
-  sk = sk_X509_new_null();
-  if (sk == NULL) {
-    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
+  uint8_t alert;
+  STACK_OF(X509) *chain = ssl_parse_cert_chain(
+      ssl, &alert,
+      ssl->ctx->retain_only_sha256_of_client_certs ? ssl->session->peer_sha256
+                                                   : NULL,
+      &certificate_msg);
+  if (chain == NULL) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
     goto err;
   }
 
-  if (!CBS_get_u24_length_prefixed(&certificate_msg, &certificate_list) ||
-      CBS_len(&certificate_msg) != 0) {
-    al = SSL_AD_DECODE_ERROR;
+  if (CBS_len(&certificate_msg) != 0) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
-    goto f_err;
-  }
-
-  while (CBS_len(&certificate_list) > 0) {
-    CBS certificate;
-    const uint8_t *data;
-
-    if (!CBS_get_u24_length_prefixed(&certificate_list, &certificate)) {
-      al = SSL_AD_DECODE_ERROR;
-      OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
-      goto f_err;
-    }
-
-    if (is_first_certificate && ssl->ctx->retain_only_sha256_of_client_certs) {
-      /* If this is the first certificate, and we don't want to keep peer
-       * certificates in memory, then we hash it right away. */
-      SHA256_Init(&sha256);
-      SHA256_Update(&sha256, CBS_data(&certificate), CBS_len(&certificate));
-      SHA256_Final(ssl->session->peer_sha256, &sha256);
-      ssl->session->peer_sha256_valid = 1;
-    }
-    is_first_certificate = 0;
-
-    /* A u24 length cannot overflow a long. */
-    data = CBS_data(&certificate);
-    x = d2i_X509(NULL, &data, (long)CBS_len(&certificate));
-    if (x == NULL) {
-      al = SSL_AD_BAD_CERTIFICATE;
-      OPENSSL_PUT_ERROR(SSL, ERR_R_ASN1_LIB);
-      goto f_err;
-    }
-    if (data != CBS_data(&certificate) + CBS_len(&certificate)) {
-      al = SSL_AD_DECODE_ERROR;
-      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_LENGTH_MISMATCH);
-      goto f_err;
-    }
-    if (!sk_X509_push(sk, x)) {
-      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
-      goto err;
-    }
-    x = NULL;
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    goto err;
   }
 
-  if (sk_X509_num(sk) <= 0) {
+  if (sk_X509_num(chain) == 0) {
     /* No client certificate so the handshake buffer may be discarded. */
     ssl3_free_handshake_buffer(ssl);
 
     /* TLS does not mind 0 certs returned */
     if (ssl->version == SSL3_VERSION) {
-      al = SSL_AD_HANDSHAKE_FAILURE;
       OPENSSL_PUT_ERROR(SSL, SSL_R_NO_CERTIFICATES_RETURNED);
-      goto f_err;
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+      goto err;
     } else if ((ssl->verify_mode & SSL_VERIFY_PEER) &&
                (ssl->verify_mode & SSL_VERIFY_FAIL_IF_NO_PEER_CERT)) {
       /* Fail for TLS only if we required a certificate */
       OPENSSL_PUT_ERROR(SSL, SSL_R_PEER_DID_NOT_RETURN_A_CERTIFICATE);
-      al = SSL_AD_HANDSHAKE_FAILURE;
-      goto f_err;
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+      goto err;
     }
   } else {
-    if (ssl_verify_cert_chain(ssl, sk) <= 0) {
-      al = ssl_verify_alarm_type(ssl->verify_result);
+    /* The hash would have been filled in. */
+    if (ssl->ctx->retain_only_sha256_of_client_certs) {
+      ssl->session->peer_sha256_valid = 1;
+    }
+
+    if (ssl_verify_cert_chain(ssl, chain) <= 0) {
       OPENSSL_PUT_ERROR(SSL, SSL_R_CERTIFICATE_VERIFY_FAILED);
-      goto f_err;
+      ssl3_send_alert(ssl, SSL3_AL_FATAL,
+                      ssl_verify_alarm_type(ssl->verify_result));
+      goto err;
     }
   }
 
   X509_free(ssl->session->peer);
-  ssl->session->peer = sk_X509_shift(sk);
+  ssl->session->peer = sk_X509_shift(chain);
   ssl->session->verify_result = ssl->verify_result;
 
   sk_X509_pop_free(ssl->session->cert_chain, X509_free);
-  ssl->session->cert_chain = sk;
+  ssl->session->cert_chain = chain;
   /* Inconsistency alert: cert_chain does *not* include the peer's own
    * certificate, while we do include it in s3_clnt.c */
 
-  sk = NULL;
-
-  ret = 1;
-
-  if (0) {
-  f_err:
-    ssl3_send_alert(ssl, SSL3_AL_FATAL, al);
-  }
+  return 1;
 
 err:
-  X509_free(x);
-  sk_X509_pop_free(sk, X509_free);
-  return ret;
+  sk_X509_pop_free(chain, X509_free);
+  return -1;
 }
 
 static int ssl3_get_client_key_exchange(SSL *ssl) {
diff --git a/ssl/internal.h b/ssl/internal.h
index 81ac76e9..a6567ab7 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -738,6 +738,15 @@ void ssl_write_buffer_clear(SSL *ssl);
  * configured and zero otherwise. */
 int ssl_has_certificate(const SSL *ssl);
 
+/* ssl_parse_cert_chain parses a certificate list from |cbs| in the format used
+ * by a TLS Certificate message. On success, it returns a newly-allocated
+ * |X509| list and advances |cbs|. Otherwise, it returns NULL and sets
+ * |*out_alert| to an alert to send to the peer. If the list is non-empty and
+ * |out_leaf_sha256| is non-NULL, it writes the SHA-256 hash of the leaf to
+ * |out_leaf_sha256|. */
+STACK_OF(X509) *ssl_parse_cert_chain(SSL *ssl, uint8_t *out_alert,
+                                     uint8_t *out_leaf_sha256, CBS *cbs);
+
 /* ssl_add_cert_to_cbb adds |x509| to |cbb|. It returns one on success and zero
  * on error. */
 int ssl_add_cert_to_cbb(CBB *cbb, X509 *x509);
diff --git a/ssl/ssl_cert.c b/ssl/ssl_cert.c
index aab86108..952bf452 100644
--- a/ssl/ssl_cert.c
+++ b/ssl/ssl_cert.c
@@ -122,6 +122,7 @@
 #include <openssl/dh.h>
 #include <openssl/err.h>
 #include <openssl/mem.h>
+#include <openssl/sha.h>
 #include <openssl/x509.h>
 #include <openssl/x509v3.h>
 
@@ -421,6 +422,59 @@ int ssl_has_certificate(const SSL *ssl) {
   return ssl->cert->x509 != NULL && ssl_has_private_key(ssl);
 }
 
+STACK_OF(X509) *ssl_parse_cert_chain(SSL *ssl, uint8_t *out_alert,
+                                     uint8_t *out_leaf_sha256, CBS *cbs) {
+  STACK_OF(X509) *ret = sk_X509_new_null();
+  if (ret == NULL) {
+    *out_alert = SSL_AD_INTERNAL_ERROR;
+    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
+    return NULL;
+  }
+
+  X509 *x = NULL;
+  CBS certificate_list;
+  if (!CBS_get_u24_length_prefixed(cbs, &certificate_list)) {
+    *out_alert = SSL_AD_DECODE_ERROR;
+    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+    goto err;
+  }
+
+  while (CBS_len(&certificate_list) > 0) {
+    CBS certificate;
+    if (!CBS_get_u24_length_prefixed(&certificate_list, &certificate)) {
+      *out_alert = SSL_AD_DECODE_ERROR;
+      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_LENGTH_MISMATCH);
+      goto err;
+    }
+
+    /* Retain the hash of the leaf certificate if requested. */
+    if (sk_X509_num(ret) == 0 && out_leaf_sha256 != NULL) {
+      SHA256(CBS_data(&certificate), CBS_len(&certificate), out_leaf_sha256);
+    }
+
+    /* A u24 length cannot overflow a long. */
+    const uint8_t *data = CBS_data(&certificate);
+    x = d2i_X509(NULL, &data, (long)CBS_len(&certificate));
+    if (x == NULL || data != CBS_data(&certificate) + CBS_len(&certificate)) {
+      *out_alert = SSL_AD_DECODE_ERROR;
+      goto err;
+    }
+    if (!sk_X509_push(ret, x)) {
+      *out_alert = SSL_AD_INTERNAL_ERROR;
+      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
+      goto err;
+    }
+    x = NULL;
+  }
+
+  return ret;
+
+err:
+  X509_free(x);
+  sk_X509_pop_free(ret, X509_free);
+  return NULL;
+}
+
 int ssl_add_cert_to_cbb(CBB *cbb, X509 *x509) {
   int len = i2d_X509(x509, NULL);
   if (len < 0) {