safety check to ensure we dont send out beyond the users buffer

ssl/s3_pkt.c

@@ -816,6 +816,21 @@ int ssl3_write_bytes(SSL *s, int type, const void *buf_, int len)
 		return tot;
 		}
 
+	/* ensure that if we end up with a smaller value of data to write 
+	 * out than the the original len from a write which didn't complete 
+	 * for non-blocking I/O and also somehow ended up avoiding 
+	 * the check for this in ssl3_write_pending/SSL_R_BAD_WRITE_RETRY as
+	 * it must never be possible to end up with (len-tot) as a large
+	 * number that will then promptly send beyond the end of the users
+	 * buffer ... so we trap and report the error in a way the user
+	 * will notice
+	 */
+	if ( len < tot)
+		{
+		SSLerr(SSL_F_SSL3_WRITE_BYTES,SSL_R_BAD_LENGTH);
+		return(-1);
+		}
+
 	n=(len-tot);
 	for (;;)
 		{