commit 26f982f50e6a7f55e41d2e7e5dec17a8e7162839
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Tue May 21 11:01:32 2019 +0200
committer Jarno Lamsa <jarno.lamsa@arm.com> Fri Aug 23 12:48:41 2019 +0300
tree 6c09496712790231061c7cb85c0802e13b5378f6
parent a7c376576058ae843b03e6b33d185849a8d80554

Improve save API by always updating olen

This allows callers to discover what an appropriate size is. Otherwise they'd
have to either try repeatedly, or allocate an overly large buffer (or some
combination of those).

Adapt documentation an example usage in ssl_client2.

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f1ba99a..6f9203d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -9862,7 +9862,7 @@
                               size_t *olen )
 {
     unsigned char *p = buf;
-    size_t left = buf_len;
+    size_t used = 0;
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 #if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
     size_t cert_len;
@@ -9874,15 +9874,16 @@
     /*
      * Shallow copy of the session structure
      */
-    if( left < sizeof( mbedtls_ssl_session ) )
-        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
-    left -= sizeof( mbedtls_ssl_session );
+    used += sizeof( mbedtls_ssl_session );
 
     /* This also copies the values of pointer fields in the
      * session to be serialized, but they'll be ignored when
      * loading the session through ssl_load_session(). */
-    memcpy( p, session, sizeof( mbedtls_ssl_session ) );
-    p += sizeof( mbedtls_ssl_session );
+    if( used <= buf_len )
+    {
+        memcpy( p, session, sizeof( mbedtls_ssl_session ) );
+        p += sizeof( mbedtls_ssl_session );
+    }
 
     /*
      * Copy of the peer's end-entity certificate
@@ -9894,40 +9895,37 @@
     else
         cert_len = session->peer_cert->raw.len;
 
-    if( left < 3 + cert_len )
-        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
-    left -= 3 + cert_len;
+    used += 3 + cert_len;
 
-    *p++ = (unsigned char)( ( cert_len >> 16 ) & 0xFF );
-    *p++ = (unsigned char)( ( cert_len >>  8 ) & 0xFF );
-    *p++ = (unsigned char)( ( cert_len       ) & 0xFF );
-    left -= 3;
-
-    if( session->peer_cert != NULL )
+    if( used <= buf_len )
     {
-        memcpy( p, session->peer_cert->raw.p, cert_len );
-        p += cert_len;
-    }
+        *p++ = (unsigned char)( ( cert_len >> 16 ) & 0xFF );
+        *p++ = (unsigned char)( ( cert_len >>  8 ) & 0xFF );
+        *p++ = (unsigned char)( ( cert_len       ) & 0xFF );
 
-    p += cert_len;
-    left -= cert_len;
+        if( session->peer_cert != NULL )
+        {
+            memcpy( p, session->peer_cert->raw.p, cert_len );
+            p += cert_len;
+        }
+    }
 #else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
     if( session->peer_cert_digest != NULL )
         cert_digest_len = 0;
     else
         cert_digest_len = session->peer_cert_digest_len;
 
-    if( left < 1 + cert_digest_len )
-        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+    used += 1 + cert_digest_len;
 
-    *p++ = (unsigned char) cert_digest_len;
-    left--;
+    if( used <= buf_len )
+    {
+        *p++ = (unsigned char) cert_digest_len;
 
-    if( session->peer_cert_digest != NULL )
-        memcpy( p, session->peer_cert_digest, cert_digest_len );
+        if( session->peer_cert_digest != NULL )
+            memcpy( p, session->peer_cert_digest, cert_digest_len );
 
-    p    += cert_digest_len;
-    left -= cert_digest_len;
+        p += cert_digest_len;
+    }
 #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
 #endif /* MBEDTLS_X509_CRT_PARSE_C */
 
@@ -9935,24 +9933,27 @@
      * Copy of the session ticket if any
      */
 #if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
-    if( left < 3 + session->ticket_len )
-        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
-    left -= 3 + session->ticket_len;
+    used += 3 + session->ticket_len;
 
-    *p++ = (unsigned char)( ( session->ticket_len >> 16 ) & 0xFF );
-    *p++ = (unsigned char)( ( session->ticket_len >>  8 ) & 0xFF );
-    *p++ = (unsigned char)( ( session->ticket_len       ) & 0xFF );
-
-    if( session->ticket != NULL )
+    if( used <= buf_len )
     {
-        memcpy( p, session->ticket, session->ticket_len );
-        p += session->ticket_len;
+        *p++ = (unsigned char)( ( session->ticket_len >> 16 ) & 0xFF );
+        *p++ = (unsigned char)( ( session->ticket_len >>  8 ) & 0xFF );
+        *p++ = (unsigned char)( ( session->ticket_len       ) & 0xFF );
+
+        if( session->ticket != NULL )
+        {
+            memcpy( p, session->ticket, session->ticket_len );
+            p += session->ticket_len;
+        }
     }
 #endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */
 
     /* Done */
-    (void) left;
-    *olen = p - buf;
+    *olen = used;
+
+    if( used > buf_len )
+        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
 
     return( 0 );
 }