Abstract:
A method, apparatus, and computer instructions for managing a data buffer. Data for the data buffer is received. A security action is performed in response to detecting data for the data buffer having a size greater than a designated size.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates generally to an improved data processing system, and in particular, to a method and apparatus for processing data. Still more particularly, the present invention provides a method and apparatus for preventing security exploits associated with buffer overflows. 
   2. Description of Related Art 
   Computers and networks are commonplace tools for many companies and businesses. Networks are used internally by a company to share information and conduct business. Often times, many types of applications and programs will be used within a network or a computer. Some of these applications and programs may be commercial packages while others may be customized for the particular client. These systems are often subject to attack or exploitation by unauthorized users. 
   For example, a hacker may attempt to gain unauthorized access to a computer system by trying to obtain a user ID and password that allows access to privileged objects within a system. Another area of concern involves security problems arising from coding errors that occur when a data buffer is allocated and data is copied into that buffer in a manner that the data “overflows” the end of the allocated storage. These types of overflows may allow an unauthorized or unprivileged subject to execute or access privileged objects in a computer or in a network. 
   For example, a command line argument may be added to a print command. If a buffer overflow is caused by the command line argument, a user may be able to print files that are normally unprintable by the particular user. 
   Another example of such a vulnerability is in Windows XP, which is an operating system available from Microsoft Corporation. With respect to universal plug and play (UPnP), an unchecked buffer is present in one of the components that handles NOTIFY directives, which are messages that advertise the availability of UPnP-capable devices on the network. By sending a specially-malformed NOTIFY directive, it would be possible for an attacker to cause code to run in the context of the UPnP service, which runs with system privileges on Windows XP. This situation would enable the attacker to gain complete control over the computer. 
   When these types of security holes or exploits are identified, programs may be patched to prevent future exploits. However, such a solution does not prevent buffer overflow exploits for programs and functions in which the bugs in coding that may allow unanticipated access remain unidentified. 
   Therefore, it would be advantageous to have an improved method, apparatus, and computer instructions for preventing security exploits based on buffer overruns. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method, apparatus, and computer instructions for managing a data buffer. Data for the data buffer is received. A security action is performed in response to detecting data for the data buffer having a size greater than a designated size. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a pictorial representation of a data processing system in which the present invention may be implemented in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a block diagram of a data processing system in which the present invention may be implemented; 
       FIG. 3  is a diagram illustrating components used in preventing security exploits based on buffer overflows in accordance with a preferred embodiment of the present invention; 
       FIG. 4  is a flowchart of a process used for preventing buffer overflow security exploits in accordance with a preferred embodiment of the present invention; and 
       FIG. 5  is a flowchart of a process used for checking limits in accordance with a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the figures and in particular with reference to  FIG. 1 , a pictorial representation of a data processing system in which the present invention may be implemented is depicted in accordance with a preferred embodiment of the present invention. A computer  100  is depicted which includes system unit  102 , video display terminal  104 , keyboard  106 , storage devices  108 , which may include floppy drives and other types of permanent and removable storage media, and mouse  110 . Additional input devices may be included with personal computer  100 , such as, for example, a joystick, touchpad, touch screen, trackball, microphone, and the like. Computer  100  can be implemented using any suitable computer, such as an IBM eServer computer or IntelliStation computer, which are products of International Business Machines Corporation, located in Armonk, N.Y. Although the depicted representation shows a computer, other embodiments of the present invention may be implemented in other types of data processing systems, such as a network computer. Computer  100  also preferably includes a graphical user interface (GUI) that may be implemented by means of systems software residing in computer readable media in operation within computer  100 . 
   With reference now to  FIG. 2 , a block diagram of a data processing system is shown in which the present invention may be implemented. Data processing system  200  is an example of a computer, such as computer  100  in  FIG. 1 , in which code or instructions implementing the processes of the present invention may be located. Data processing system  200  employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Accelerated Graphics Port (AGP) and Industry Standard Architecture (ISA) may be used. Processor  202  and main memory  204  are connected to PCI local bus  206  through PCI bridge  208 . PCI bridge  208  also may include an integrated memory controller and cache memory for processor  202 . Additional connections to PCI local bus  206  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  210 , small computer system interface SCSI host bus adapter  212 , and expansion bus interface  214  are connected to PCI local bus  206  by direct component connection. In contrast, audio adapter  216 , graphics adapter  218 , and audio/video adapter  219  are connected to PCI local bus  206  by add-in boards inserted into expansion slots. Expansion bus interface  214  provides a connection for a keyboard and mouse adapter  220 , modem  222 , and additional memory  224 . SCSI host bus adapter  212  provides a connection for hard disk drive  226 , tape drive  228 , and CD-ROM drive  230 . Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors. 
   An operating system runs on processor  202  and is used to coordinate and provide control of various components within data processing system  200  in  FIG. 2 . The operating system may be a commercially available operating system such as Windows XP, which is available from Microsoft Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provides calls to the operating system from Java programs or applications executing on data processing system  200 . “Java” is a trademark of Sun Microsystems, Inc. Instructions for the operating system, the object-oriented programming system, and applications or programs are located on storage devices, such as hard disk drive  226 , and may be loaded into main memory  204  for execution by processor  202 . 
   Those of ordinary skill in the art will appreciate that the hardware in  FIG. 2  may vary depending on the implementation. Other internal hardware or peripheral devices, such as flash read-only memory (ROM), equivalent nonvolatile memory, or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in  FIG. 2 . Also, the processes of the present invention may be applied to a multiprocessor data processing system. 
   For example, data processing system  200 , if optionally configured as a network computer, may not include SCSI host bus adapter  212 , hard disk drive  226 , tape drive  228 , and CD-ROM  230 . In that case, the computer, to be properly called a client computer, includes some type of network communication interface, such as LAN adapter  210 , modem  222 , or the like. As another example, data processing system  200  may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system  200  comprises some type of network communication interface. As a further example, data processing system  200  may be a personal digital assistant (PDA), which is configured with ROM and/or flash ROM to provide non-volatile memory for storing operating system files and/or user-generated data. 
   The depicted example in  FIG. 2  and above-described examples are not meant to imply architectural limitations. For example, data processing system  200  also may be a notebook computer or hand held computer in addition to taking the form of a PDA. Data processing system  200  also may be a kiosk or a Web appliance. 
   The processes of the present invention are performed by processor  202  using computer implemented instructions, which may be located in a memory such as, for example, main memory  204 , memory  224 , or in one or more peripheral devices  226 – 230 . 
   Turning now to  FIG. 3 , a diagram illustrating components used in preventing security exploits based on buffer overflows is depicted in accordance with a preferred embodiment of the present invention. In this example, data buffer  300  is a location in which data may be copied into for executing functions and processes. Data is written into data buffer  300  by process  302  in this example. The mechanism of the present invention includes security process  304 , which is designed to place limitations on the size of individual input parameters to prevent environmental variables and command line arguments from exceeding a selected size. Environmental variables are symbolic names used to provide information. For example, on UNIX-like operating systems, the HOME environmental variable contains the name of the current user&#39;s home directory. This environmental variable may be used by commands to determine where to store files which would normally be stored in the user&#39;s home directory. Another example is the NLSPATH environmental variable. This environmental variable is used to construct the name of the message files used by programs so that the program can produce messages in the appropriate language using the appropriate cultural conventions. Command line arguments are values passed with a command typed into a command line. These arguments are independent items, or variables, that contain data or codes. 
   Of course, the mechanism of the present invention may be implemented in other components, such as, for example, within the operating system or as an extension to the operating system such as systems, which provide an ability to load additional security policies. Depending on the size of the data placed into data buffer  300 , security process  304  initiates a security action, which may include for example, preventing a program from acting on or using the data or logging a warning message. This message may contain information needed to identify the program or user initiating placement of the data into data buffer  300 . 
   In these examples, an input into data buffer  300  are divided into two types, environmental variables and command line arguments. Further, two types of limitations are placed on the length of inputs in data buffer  300 . For example, a soft limit is used to produce a warning message in the system error log for audit trail when this limit is exceeded when data is placed into data buffer  300 . A hard limit also is used, which causes command execution to fail, when this limit is exceeded. 
   The mechanism of the present invention also may look to see what privileges are present. For example, execution of a privileged object by an unprivileged subject and execution of any object by a privileged subject are situations in which the mechanism of the present invention checks for buffer overflows. With respect to these two instances, these situations represent instances in which the privilege is enhanced, which is a more common scenario for violating security in a computer system or network. The situation in which an unprivileged object is executed by an unprivileged subject is not assumed to represent a security risk or exposure in these examples. 
   With reference now to  FIG. 4 , a flowchart of a process used for preventing buffer overflow security exploits is depicted in accordance with a preferred embodiment of the present invention. The process illustrated in  FIG. 4  may be implemented in a security process, such as security process  304  in  FIG. 3 . 
   The process begins by making a determination as to whether the process has privileges (step  400 ). In these examples, a privilege allows a process to perform an operation that the process normally would not be permitted to perform absent the privilege. A privilege may be required to access objects or to perform operations. The objects accessed may be, for example, files, devices, and memory segments. The operations may be, for example, adding users, modifying an audit system, and configuring devices. If the process does not have privileges, a determination is made as to whether the process is acquiring privileges (step  402 ). Printing of a document is an example of an operation of a process in which a process may acquire a privilege. A process which spools print requests must be able to write to the directory which contains print requests. An ordinary process lacks the privileges needed to perform this operation. The process temporarily acquires privilege while running the print command so that the print command may spool the print request. If the process is not acquiring privileges, the program is permitted (step  404 ) and the process terminates thereafter. This situation is one in which an unprivileged object is executed by an unprivileged subject or process and is assumed not to present a security risk or exposure. 
   With reference again to step  402 , if the process is acquiring privileges, limit values for processes acquiring privileges are used (step  406 ). In these examples, a total of eight limits, which may be defined by a 2×2×2 matrix, are present. One dimension is an environmental variable or a command line argument, while another dimension is a privilege process or a privilege acquiring process. The third dimension is a soft limit or hard limit. In these examples, the soft limit causes a logging of the operation while the hard limit also results in a termination or prohibition of process execution. Of the eight limits total, four are selected based on already privileged versus privilege acquiring. Of those four limits, two are selected based on whether the system is checking environmental variables or command line arguments at that instant. Limit checking is performed (step  408 ) and the process terminates thereafter. With reference again to step  400 , if the process has privileges, limit values for processes which already have privileges are used (step  410 ) and the process proceeds to step  408  as described above. 
   Turning now to  FIG. 5 , a flowchart of a process used for checking limits is depicted in accordance with a preferred embodiment of the present invention. The process illustrated in  FIG. 5  is a more detailed description of step  408  in  FIG. 4 . 
   The process begins by making a determination as to whether any remaining environmental variables are present for processing (step  500 ). If more environmental variables are not present for processing, a determination is made as to whether any remaining command line arguments are present for processing (step  502 ). If more command line arguments are not present for processing, the program is permitted to proceed executing with the environmental variables or command line arguments placed in the buffer (step  504 ) and the process terminates thereafter. 
   With reference again to step  502 , if more remaining command line arguments are present for processing, a determination is made as to whether the length of the command line argument being processed exceeds a hard limit (step  506 ). If the length does exceed the hard limit, the program is not permitted to continue execution, a message is logged and the program fails (step  508 ) with the process terminating thereafter. 
   The message may be stored in a log or other file for later use. In these examples, the message includes information about the object in which access was attempted and information about the process attempting the access. For example, the message may include the name of a file, a path to the file, and an identification of the process attempting the access. Further, this information also may include a user ID for the user logged in at the time the access attempt failed. Any other information useful for identifying the subject or process attempting to access the object may be included in the message. For example, information about the date and length of data placed in the buffer may be logged as well as a process ID, and connection information. 
   If the length does not exceed the hard limit, a determination is made as to whether the length exceeds the soft limit (step  510 ). If the length does not exceed the hard limit, the next unprocessed argument in the buffer is selected for processing (step  512 ) and the process returns to step  502  as described above. If the length does exceed the soft limit, a warning message is logged (step  514 ) and the proceeds to step  512  as described above. This warning message may include information similar to messages logged when program execution is not permitted. 
   With reference again to step  500 , if more remaining environmental variables are present for processing, a determination is made as to whether the length of the environmental variable exceeds the hard limit (step  516 ). If the length does exceed the hard limit, the program is not permitted, the message is logged and the program fails (step  518 ) with the process terminating thereafter. If the length does not exceed the hard limit, a determination is made as to whether the length exceeds the soft limit (step  520 ). If the length does not exceeds the hard limit, the next variable is selected for processing (step  522 ) and the process returns to step  500 , as described above, to determine whether another environmental variable was present and selected by step  522 . If the length does exceed the soft limit, a warning message is logged (step  524 ) and the proceeds to step  522  as described above. 
   The particular limits selected for the hard limit and the soft limit depend on the particular implementation. For example, a soft limit for a user name may be 16 Kbytes while a hard limit is 20 Kbytes. Further, the hard limit for the environmental variable may differ from the hard limit for the command line argument. Further, the soft limits may differ between an environmental variable and a command line argument. 
   Thus, the present invention provides an improved method, apparatus, and computer instructions for preventing buffer overflow security exploits. When a potential security risk or exposure is present, the mechanism of the present invention checks to see whether data input into the buffer exceeds selected limits or thresholds. Depending on what thresholds are exceeded, a warning message may be logged or execution of the program may be prevented. In this manner, exploitation of unknown or undiscovered security holds or risks may be prevented. 
   It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system. 
   The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.