Certain fields in the protcol required a strict formatting. If

off bound values were sent to the server this could under some
circumstances lead to a crash on the Windows platform.

sql/sql_connect.cc

@@ -630,6 +630,94 @@ bool init_new_connection_handler_thread()
   return 0;
 }
 
+#ifndef EMBEDDED_LIBRARY
+/**
+  Get a null character terminated string from a user-supplied buffer.
+
+  @param buffer[in, out]    Pointer to the buffer to be scanned.
+  @param max_bytes_available[in, out]  Limit the bytes to scan.
+  @param string_length[out] The number of characters scanned not including
+                            the null character.
+
+  @remark The string_length does not include the terminating null character.
+          However, after the call, the buffer is increased by string_length+1
+          bytes, beyond the null character if there still available bytes to
+          scan.
+
+  @return pointer to beginning of the string scanned.
+    @retval NULL The buffer content is malformed
+*/
+
+static
+char *get_null_terminated_string(char **buffer,
+                                 size_t *max_bytes_available,
+                                 size_t *string_length)
+{
+  char *str= (char *)memchr(*buffer, '\0', *max_bytes_available);
+
+  if (str == NULL)
+    return NULL;
+
+  *string_length= (size_t)(str - *buffer);
+  *max_bytes_available-= *string_length + 1;
+  str= *buffer;
+  *buffer += *string_length + 1;  
+
+  return str;
+}
+
+
+/**
+  Get a length encoded string from a user-supplied buffer.
+
+  @param buffer[in, out] The buffer to scan; updates position after scan.
+  @param max_bytes_available[in, out] Limit the number of bytes to scan
+  @param string_length[out] Number of characters scanned
+  
+  @remark In case the length is zero, then the total size of the string is
+    considered to be 1 byte; the size byte.
+
+  @return pointer to first byte after the header in buffer.
+    @retval NULL The buffer content is malformed
+*/
+
+static
+char *get_length_encoded_string(char **buffer,
+                                size_t *max_bytes_available,
+                                size_t *string_length)
+{
+  if (*max_bytes_available == 0)
+    return NULL;
+
+  /* Do double cast to prevent overflow from signed / unsigned conversion */
+  size_t str_len= (size_t)(unsigned char)**buffer;
+
+  /*
+    If the length encoded string has the length 0
+    the total size of the string is only one byte long (the size byte)
+  */
+  if (str_len == 0)
+  {
+    ++*buffer;
+    *string_length= 0;
+    /*
+      Return a pointer to the 0 character so the return value will be
+      an empty string.
+    */
+    return *buffer-1;
+  }
+
+  if (str_len >= *max_bytes_available)
+    return NULL;
+
+  char *str= *buffer+1;
+  *string_length= str_len;
+  *max_bytes_available-= *string_length + 1;
+  *buffer+= *string_length + 1;
+  return str;
+}
+
+
 /*
   Perform handshake, authorize client and update thd ACL variables.
 
@@ -643,7 +731,6 @@ bool init_new_connection_handler_thread()
    > 0  error code (not sent to user)
 */
 
-#ifndef EMBEDDED_LIBRARY
 static int check_connection(THD *thd)
 {
   uint connect_errors= 0;
@@ -831,7 +918,7 @@ static int check_connection(THD *thd)
   }
 #endif /* HAVE_OPENSSL */
 
-  if (end >= (char*) net->read_pos+ pkt_len +2)
+  if (end > (char *)net->read_pos + pkt_len)
   {
     inc_host_errors(&thd->remote.sin_addr);
     my_error(ER_HANDSHAKE_ERROR, MYF(0), thd->main_security_ctx.host_or_ip);
@@ -843,39 +930,75 @@ static int check_connection(THD *thd)
   if ((thd->client_capabilities & CLIENT_TRANSACTIONS) &&
       opt_using_transactions)
     net->return_status= &thd->server_status;
-
+ 
-  char *user= end;
-  char *passwd= strend(user)+1;
-  uint user_len= passwd - user - 1;
-  char *db= passwd;
-  char db_buff[NAME_LEN + 1];           // buffer to store db in utf8
-  char user_buff[USERNAME_LENGTH + 1];	// buffer to store user in utf8
-  uint dummy_errors;
-
   /*
-    Old clients send null-terminated string as password; new clients send
+    In order to safely scan a head for '\0' string terminators
-    the size (1 byte) + string (not null-terminated). Hence in case of empty
+    we must keep track of how many bytes remain in the allocated
-    password both send '\0'.
+    buffer or we might read past the end of the buffer.
-
-    This strlen() can't be easily deleted without changing protocol.
-
-    Cast *passwd to an unsigned char, so that it doesn't extend the sign for
-    *passwd > 127 and become 2**32-127+ after casting to uint.
   */
-  uint passwd_len= thd->client_capabilities & CLIENT_SECURE_CONNECTION ?
+  size_t bytes_remaining_in_packet= pkt_len - (end - (char *)net->read_pos);
-    (uchar)(*passwd++) : strlen(passwd);
-  db= thd->client_capabilities & CLIENT_CONNECT_WITH_DB ?
-    db + passwd_len + 1 : 0;
-  /* strlen() can't be easily deleted without changing protocol */
-  uint db_len= db ? strlen(db) : 0;
 
-  if (passwd + passwd_len + db_len > (char *)net->read_pos + pkt_len)
+  size_t user_len;
+  char *user= get_null_terminated_string(&end, &bytes_remaining_in_packet,
+                                         &user_len);
+  if (user == NULL)
   {
     inc_host_errors(&thd->remote.sin_addr);
     my_error(ER_HANDSHAKE_ERROR, MYF(0), thd->main_security_ctx.host_or_ip);
     return 1;
   }
 
+  /*
+    Old clients send a null-terminated string as password; new clients send
+    the size (1 byte) + string (not null-terminated). Hence in case of empty
+    password both send '\0'.
+  */
+  size_t passwd_len= 0;
+  char *passwd= NULL;
+
+  if (thd->client_capabilities & CLIENT_SECURE_CONNECTION)
+  {
+    /*
+      4.1+ password. First byte is password length.
+    */
+    passwd= get_length_encoded_string(&end, &bytes_remaining_in_packet,
+                                      &passwd_len);
+  }
+  else
+  {
+    /*
+      Old passwords are zero terminated strings.
+    */
+    passwd= get_null_terminated_string(&end, &bytes_remaining_in_packet,
+                                       &passwd_len);
+  }
+
+  if (passwd == NULL)
+  {
+    inc_host_errors(&thd->remote.sin_addr);
+    my_error(ER_HANDSHAKE_ERROR, MYF(0), thd->main_security_ctx.host_or_ip);
+    return 1;
+  }
+
+  size_t db_len= 0;
+  char *db= NULL;
+
+  if (thd->client_capabilities & CLIENT_CONNECT_WITH_DB)
+  {
+    db= get_null_terminated_string(&end, &bytes_remaining_in_packet,
+                                   &db_len);
+    if (db == NULL)
+    {
+      inc_host_errors(&thd->remote.sin_addr);
+      my_error(ER_HANDSHAKE_ERROR, MYF(0), thd->main_security_ctx.host_or_ip);
+      return 1;
+    }
+  }
+
+  char db_buff[NAME_LEN + 1];           // buffer to store db in utf8
+  char user_buff[USERNAME_LENGTH + 1];	// buffer to store user in utf8
+  uint dummy_errors;
+
   /* Since 4.1 all database names are stored in utf8 */
   if (db)
   {