MDEV-22387: Do not violate __attribute__((nonnull))

Passing a null pointer to a nonnull argument is not only undefined
behaviour, but it also grants the compiler the permission to optimize
away further checks whether the pointer is null. GCC -O2 at least
starting with version 8 may do that, potentially causing SIGSEGV.

1 files changed, 5 insertions, 3 deletions

diff --git a/sql/protocol.cc b/sql/protocol.cc
index aa795b9d12a..de6d1b96f76 100644
--- a/sql/protocol.cc
+++ b/sql/protocol.cc
@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2012, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2012, Monty Program Ab
+   Copyright (c) 2008, 2020, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -58,7 +58,8 @@ bool Protocol_binary::net_store_data(const uchar *from, size_t length)
       packet->realloc(packet_length+9+length))
     return 1;
   uchar *to= net_store_length((uchar*) packet->ptr()+packet_length, length);
-  memcpy(to,from,length);
+  if (length)
+    memcpy(to,from,length);
   packet->length((uint) (to+length-(uchar*) packet->ptr()));
   return 0;
 }
@@ -715,7 +716,8 @@ void net_send_progress_packet(THD *thd)
 uchar *net_store_data(uchar *to, const uchar *from, size_t length)
 {
   to=net_store_length_fast(to,length);
-  memcpy(to,from,length);
+  if (length)
+    memcpy(to,from,length);
   return to+length;
 }