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All built-in integral types (char, short, int, long, etc) have a limited capacity because they are represented with a xed number of bits Sometimes programmers ignore this fact and think of an integral variable as being the same as an integer in mathematics (where an integer has no nite upper or lower bound) Unlike integers in mathematics, program variables have a xed range and wrap around when they go above their maximum value or below their minimum value; a very large positive number becomes a very large negative number, or vice versa Figure 71 shows the range of values that can be represented by 4-bit signed and unsigned variables1 Figure 72 shows how, with an unsigned 4-bit variable, 15 + 1 = 0 Similarly, with a signed 4-bit variable, 7 + 1 = -8 When an attacker can take advantage of this behavior, the program is said to contain an integer over ow vulnerability Integer over ow can lead to any number of problems, but in C and C++, an integer over ow is most frequently used as a lead-in to a buffer over ow exploit The buffer over ow might occur when the wrapped-around variable is used to allocate memory, bound a string operation, or index into a buffer Integer over ow can also occur in Java, but because Java enforces memory safety properties, integer over ow is not as easy to exploit In this section, we discuss a variety of ways that integer overflow and numeric conversion errors can occur and suggest tactics for avoiding them in common scenarios We also look at some closely related typeconversion bugs At the end of the section, we demonstrate techniques to prevent or detect these problems in situations that are most likely to cause vulnerabilities Wrap-Around Errors Wrap-around errors, the canonical example of integer over ows, occur when an integer value is increased or decreased to a value outside the range its data type is capable of representing Example 71 shows an excerpt from OpenSSH 33 that demonstrates a classic case of integer over ow If nresp has the value 1073741824 and sizeof(char*) has its typical value of 4, the result of the operation nresp*sizeof(char*) over ows, and the argument to xmalloc() will be 0 Because the allocated buffer is greatly undersized, the subsequent loop iterations will over ow the heap buffer response.

It is possible to use Active Record s underlying database connections directly, and sometimes it is useful to do so from custom scripts and for one-off or ad-hoc testing Access the connection via the connection attribute of any Active Record class If all your models use the same connection, then use the connection attribute of ActiveRecord::Base

A property con guration can be made mandatory by setting the mustSupply attribute on the property declaration in the composite to true (by default, it is set to false) This is shown in Listing 520

The most basic operation that you can do with a connection is simply to execute a SQL statement from the DatabaseStatements module For example, Listing 51 shows a method that executes a SQL file statement by statement

1 We assume that all signed numbers are represented using twos compliment This is the representation almost all modern computers use

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Listing 51 Execute a SQL file line by line using active record s connection def execute_sql_file(path) Fileread(path)split(';')each do |sql| begin ActiveRecord::Baseconnectionexecute(#{sql}\n") unless sqlblank rescue ActiveRecord::StatementInvalid $stderrputs "warning: #{$!}" end end end

The ActiveRecord::ConnectionAdapters::DatabaseStatements module mixes a number of useful methods into the connection object that make it possible to work with the database directly instead of using Active Record models I ve purposely left out some of the methods of this module (such as add_limit! and add_lock) because they

are used internally by Rails to construct SQL statements dynamically and I don t think they re of much use to application developers For the sake of readability in the select_examples below, assume that the connection object has been assigned to conn, like this:

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begin db transaction()

<composite name="CreditServiceComposite" xmlns:xs="http://wwww3org/2001/XMLSchema"> <property name="min" mustSupply="true" type="xs:integer"/> <property name="max" mustSupply="true" type="xs:integer"/> <component name ="CreditComponent"> <component> </composite>

Begins a database transaction manually (and turns off Active Record s default autocommitting behavior)

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commit db transaction()

Commits the transaction (and turns on Active Record s default autocommitting behavior again)

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delete(sql statement)

When @mustSupply is set to true, a property must be con gured when the composite is used as a component implementation

execute(sql statement)

Executes the SQL statement provided in the context of this connection This method is abstract in the DatabaseStatements module and is overridden by specific database adapter implementations As such, the return type is a result set object corresponding to the adapter in use

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insert(sql statement)

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