Homework 6

22C:116, Fall 1999

Due Friday Oct 1, 1999, in class

1. Background Recordable CD-Roms are an example of a WORM memory device (Write Once Read Mostly). EPROM is another example of such a device. In both cases, it the blank memory device has all bits set to 1 (or 0), and, under software control, each bit can be set to 0 (or 1) at any time, but once a bit is changed, the change can never be undone. EPROMS are word addressable, while Recordable CD-Roms have random-access characteristics like other disks.

   Certain applications can greatly benefit from the use of WORM devices, but it is generally desirable to make the WORM device present a standard file system interface to the rest of the system software.

   Part A: What storage allocation or free list management scheme would you suggest using to manage the free space on a WORM.

   Part B: When a user creates a new version of /local_user/jones/temp on a WORM, what files must be replaced by new versions.

   Part C: How would you suggest finding the root of the file system on a WORM when the file system is mounted.

2. The Question: Macro viruses attached to Microsoft Word documents are a major problem today. Given what you know about the requirements a virus must meet in order to propagate through a computer system (see section 4.4 of the text) what features can you infer must be present in Microsoft Word's macro language.

3. The Question Protection models that include domains as objects allow the operation "enter" to be executed, transferring control from one domain to another. What operations permitted in a conventional 2-level security model (user state/system state) are formally modeled as enter operations? (See section 4.5.1 of the text)

4. The Question Read the man page for the UNIX chmod and exec commands. What feature of CHMOD and the setuid bit prevent the use of the setuid bit to solve the mutual suspicion problem?