Bug#25471090: MYSQL USE AFTER FREE

Description:- Mysql client crashes when trying to connect
to a fake server which is sending incorrect packets.

Analysis:- Mysql client crashes when it tries to read
server version details.

Fix:- A check is added in "red_one_row()".

Author: Arun Kuruvila

include/mysql_com.h

@@ -1,4 +1,4 @@
-/* Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
 
    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
@@ -561,6 +561,7 @@ void my_thread_end(void);
 
 #ifdef _global_h
 ulong STDCALL net_field_length(uchar **packet);
+ulong STDCALL net_field_length_checked(uchar **packet, ulong max_length);
 my_ulonglong net_field_length_ll(uchar **packet);
 uchar *net_store_length(uchar *pkg, ulonglong length);
 #endif

sql-common/client.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
 
    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
@@ -1723,18 +1723,20 @@ read_one_row(MYSQL *mysql,uint fields,MYSQL_ROW row, ulong *lengths)
   end_pos=pos+pkt_len;
   for (field=0 ; field < fields ; field++)
   {
-    if ((len=(ulong) net_field_length(&pos)) == NULL_LENGTH)
+    len=(ulong) net_field_length_checked(&pos, (ulong)(end_pos - pos));
+    if (pos > end_pos)
+    {
+      set_mysql_error(mysql, CR_UNKNOWN_ERROR, unknown_sqlstate);
+      return -1;
+    }
+
+    if (len == NULL_LENGTH)
     {						/* null field */
       row[field] = 0;
       *lengths++=0;
     }
     else
     {
-      if (len > (ulong) (end_pos - pos))
-      {
-        set_mysql_error(mysql, CR_UNKNOWN_ERROR, unknown_sqlstate);
-        return -1;
-      }
       row[field] = (char*) pos;
       pos+=len;
       *lengths++=len;

sql-common/pack.c

@@ -1,5 +1,4 @@
-/* Copyright (c) 2000-2003, 2007 MySQL AB
-   Use is subject to license terms
+/* Copyright (c) 2000, 2018 Oracle and/or its affiliates. All rights reserved.
 
    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
@@ -46,6 +45,40 @@ ulong STDCALL net_field_length(uchar **packet)
   return (ulong) uint4korr(pos+1);
 }
 
+/* The same as above but with max length check */
+ulong STDCALL net_field_length_checked(uchar **packet, ulong max_length)
+{
+  ulong len;
+  uchar *pos= (uchar *)*packet;
+
+  if (*pos < 251)
+  {
+    (*packet)++;
+    len= (ulong) *pos;
+    return (len > max_length) ? max_length : len;
+  }
+  if (*pos == 251)
+  {
+    (*packet)++;
+    return NULL_LENGTH;
+  }
+  if (*pos == 252)
+  {
+    (*packet)+=3;
+    len= (ulong) uint2korr(pos+1);
+    return (len > max_length) ? max_length : len;
+  }
+  if (*pos == 253)
+  {
+    (*packet)+=4;
+    len= (ulong) uint3korr(pos+1);
+    return (len > max_length) ? max_length : len;
+  }
+  (*packet)+=9;                                 /* Must be 254 when here */
+  len= (ulong) uint4korr(pos+1);
+  return (len > max_length) ? max_length : len;
+}
+
 /* The same as above but returns longlong */
 my_ulonglong net_field_length_ll(uchar **packet)
 {