From a2fce21ae5b5bd74c66e305f864ff5875cf9df81 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= <mpg@elzevir.fr>
Date: Wed, 15 Apr 2015 19:09:03 +0200
Subject: [PATCH] Fix potential NULL dereference on bad usage

---
 ChangeLog         |  3 ++
 library/ssl_tls.c | 71 ++++++++++++++++++++++++++++-------------------
 2 files changed, 46 insertions(+), 28 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index edcd42dd3..39ae43f82 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -27,6 +27,9 @@ Features
      errors on use of deprecated functions.
 
 Bugfix
+   * Fix potential NULL pointer dereference (not trigerrable remotely) when
+     ssl_write() is called before the handshake is finished (introduced in
+     1.3.10) (first reported by Martin Blumenstingl).
    * Fix bug in pk_parse_key() that caused some valid private EC keys to be
      rejected.
    * Fix bug in Via Padlock support (found by Nikos Mavrogiannopoulos).
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 515b90355..d2e0c52bc 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4754,37 +4754,16 @@ int ssl_read( ssl_context *ssl, unsigned char *buf, size_t len )
 }
 
 /*
- * Send application data to be encrypted by the SSL layer
+ * Send application data to be encrypted by the SSL layer,
+ * taking care of max fragment length and buffer size
  */
-#if defined(POLARSSL_SSL_CBC_RECORD_SPLITTING)
-static int ssl_write_real( ssl_context *ssl, const unsigned char *buf, size_t len )
-#else
-int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
-#endif
+static int ssl_write_real( ssl_context *ssl,
+                           const unsigned char *buf, size_t len )
 {
     int ret;
     size_t n;
     unsigned int max_len = SSL_MAX_CONTENT_LEN;
 
-    SSL_DEBUG_MSG( 2, ( "=> write" ) );
-
-#if defined(POLARSSL_SSL_RENEGOTIATION)
-    if( ( ret = ssl_check_ctr_renegotiate( ssl ) ) != 0 )
-    {
-        SSL_DEBUG_RET( 1, "ssl_check_ctr_renegotiate", ret );
-        return( ret );
-    }
-#endif
-
-    if( ssl->state != SSL_HANDSHAKE_OVER )
-    {
-        if( ( ret = ssl_handshake( ssl ) ) != 0 )
-        {
-            SSL_DEBUG_RET( 1, "ssl_handshake", ret );
-            return( ret );
-        }
-    }
-
 #if defined(POLARSSL_SSL_MAX_FRAGMENT_LENGTH)
     /*
      * Assume mfl_code is correct since it was checked when set
@@ -4824,8 +4803,6 @@ int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
         }
     }
 
-    SSL_DEBUG_MSG( 2, ( "<= write" ) );
-
     return( (int) n );
 }
 
@@ -4837,7 +4814,8 @@ int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
  * remember wether we already did the split or not.
  */
 #if defined(POLARSSL_SSL_CBC_RECORD_SPLITTING)
-int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
+static int ssl_write_split( ssl_context *ssl,
+                            const unsigned char *buf, size_t len )
 {
     int ret;
 
@@ -4865,6 +4843,43 @@ int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
 }
 #endif /* POLARSSL_SSL_CBC_RECORD_SPLITTING */
 
+/*
+ * Write application data (public-facing wrapper)
+ */
+int ssl_write( ssl_context *ssl, const unsigned char *buf, size_t len )
+{
+    int ret;
+
+    SSL_DEBUG_MSG( 2, ( "=> write" ) );
+
+#if defined(POLARSSL_SSL_RENEGOTIATION)
+    if( ( ret = ssl_check_ctr_renegotiate( ssl ) ) != 0 )
+    {
+        SSL_DEBUG_RET( 1, "ssl_check_ctr_renegotiate", ret );
+        return( ret );
+    }
+#endif
+
+    if( ssl->state != SSL_HANDSHAKE_OVER )
+    {
+        if( ( ret = ssl_handshake( ssl ) ) != 0 )
+        {
+            SSL_DEBUG_RET( 1, "ssl_handshake", ret );
+            return( ret );
+        }
+    }
+
+#if defined(POLARSSL_SSL_CBC_RECORD_SPLITTING)
+    ret = ssl_write_split( ssl, buf, len );
+#else
+    ret = ssl_write_real( ssl, buf, len );
+#endif
+
+    SSL_DEBUG_MSG( 2, ( "<= write" ) );
+
+    return( ret );
+}
+
 /*
  * Notify the peer that the connection is being closed
  */