Postpone freeing of X509 context to the first data exchange after handshake

X509 context contains certificate fingerprint and various names which may be used to verify the certificate.
Previously we would free it right after the handshake completion, which prevented the client from actually using any information from X509 context.
Postponing this to the first ssl_read/ssl_write call after the handshake, we give the client a chance to verify the certificate.

Also added logging to ssl_match_fingerprint function in case fingerprint doesn't match expected value.

Author: igrr

ssl/tls1.c

@@ -52,6 +52,7 @@ static int set_key_block(SSL *ssl, int is_write);
 static int verify_digest(SSL *ssl, int mode, const uint8_t *buf, int read_len);
 static void *crypt_new(SSL *ssl, uint8_t *key, uint8_t *iv, int is_decrypt, void* cached);
 static int send_raw_packet(SSL *ssl, uint8_t protocol);
+static void certificate_free(SSL* ssl);
 
 /**
  * The server will pick the cipher based on the order that the order that the
@@ -247,8 +248,8 @@ EXP_FUNC void STDCALL ssl_free(SSL *ssl)
     free(ssl->encrypt_ctx);
     free(ssl->decrypt_ctx);
     disposable_free(ssl);
+    certificate_free(ssl);
     free(ssl->bm_all_data);
-    free(ssl->fingerprint);
     free(ssl);
 }
 
@@ -257,6 +258,9 @@ EXP_FUNC void STDCALL ssl_free(SSL *ssl)
  */
 EXP_FUNC int STDCALL ssl_read(SSL *ssl, uint8_t **in_data)
 {
+    if (ssl->hs_status == SSL_OK) {
+        certificate_free(ssl);
+    }
     int ret = basic_read(ssl, in_data);
 
     /* check for return code so we can send an alert */
@@ -281,7 +285,9 @@ EXP_FUNC int STDCALL ssl_read(SSL *ssl, uint8_t **in_data)
 EXP_FUNC int STDCALL ssl_write(SSL *ssl, const uint8_t *out_data, int out_len)
 {
     int n = out_len, nw, i, tot = 0;
-
+    if (ssl->hs_status == SSL_OK) {
+        certificate_free(ssl);
+    }
     /* maximum size of a TLS packet is around 16kB, so fragment */
     do 
     {
@@ -547,7 +553,6 @@ SSL *ssl_new(SSL_CTX *ssl_ctx, int client_fd)
     ssl->ca_cert_ctx = ssl_ctx->ca_cert_ctx;
 #endif
     disposable_new(ssl);
-    ssl->fingerprint = 0;
 
     /* a bit hacky but saves a few bytes of memory */
     ssl->flag |= ssl_ctx->options;
@@ -1671,12 +1676,17 @@ void disposable_free(SSL *ssl)
         free(ssl->dc);
         ssl->dc = NULL;
     }
+}
+
+static void certificate_free(SSL* ssl)
+{
 #ifdef CONFIG_SSL_CERT_VERIFICATION
     if (ssl->x509_ctx) {
         x509_free(ssl->x509_ctx);
         ssl->x509_ctx = 0;
     }
 #endif
+    increase_bm_data_size(ssl);
 }
 
 #ifndef CONFIG_SSL_SKELETON_MODE     /* no session resumption in this mode */
@@ -1945,9 +1955,21 @@ int process_certificate(SSL *ssl, X509_CTX **x509_ctx)
 
 EXP_FUNC int STDCALL ssl_match_fingerprint(const SSL *ssl, const uint8_t* fp)
 {
-    if (!ssl->fingerprint)
+    if (ssl->x509_ctx == NULL || ssl->x509_ctx->fingerprint == NULL)
         return 1;
-    return memcmp(ssl->fingerprint, fp, SHA1_SIZE);
+    int res = memcmp(ssl->x509_ctx->fingerprint, fp, SHA1_SIZE);
+    if (res != 0) {
+        printf("cert FP: ");
+        for (int i = 0; i < SHA1_SIZE; ++i) {
+            printf("%02X ", ssl->x509_ctx->fingerprint[i]);
+        }
+        printf("\r\ntest FP: ");
+        for (int i = 0; i < SHA1_SIZE; ++i) {
+            printf("%02X ", fp[i]);
+        }
+        printf("\r\n");
+    }
+    return res;
 }
 
 #endif /* CONFIG_SSL_CERT_VERIFICATION */

ssl/tls1.h

@@ -190,8 +190,6 @@ struct _SSL
 #ifdef CONFIG_SSL_CERT_VERIFICATION
     X509_CTX *x509_ctx;
 #endif
-    uint8_t* fingerprint;
-
     uint8_t session_id[SSL_SESSION_ID_SIZE]; 
     uint8_t client_mac[SHA1_SIZE];  /* for HMAC verification */
     uint8_t server_mac[SHA1_SIZE];  /* for HMAC verification */

ssl/tls1_clnt.c

@@ -119,10 +119,7 @@ int do_clnt_handshake(SSL *ssl, int handshake_type, uint8_t *buf, int hs_len)
 
         case HS_FINISHED:
             ret = process_finished(ssl, buf, hs_len);
-            ssl->fingerprint = ssl->x509_ctx->fingerprint;
-            ssl->x509_ctx->fingerprint = 0;
-            disposable_free(ssl);   /* free up some memory */
-            increase_bm_data_size(ssl);
+            disposable_free(ssl);
             /* note: client renegotiation is not allowed after this */
             break;