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lecture_10 - Operating System Security CS 136 Computer...

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Lecture 10 Page 1 CS 136, Winter 2010 Operating System Security CS 136 Computer Security Peter Reiher February 4, 2010
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Lecture 10 Page 2 CS 136, Winter 2010 Outline Interprocess communications protection File protection and disk encryption Protecting other OS resources Logging and auditing
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Lecture 10 Page 3 CS 136, Winter 2010 Protecting Interprocess Communications Operating systems provide various kinds of interprocess communications Messages Semaphores Shared memory Sockets How can we be sure they’re used properly?
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Lecture 10 Page 4 CS 136, Winter 2010 IPC Protection Issues How hard it is depends on what you’re worried about For the moment, let’s say we’re worried about one process improperly using IPC to get info from another Process A wants to steal information from process B How would process A do that?
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Lecture 10 Page 5 CS 136, Winter 2010 Message Security Process A Process B Can process B use message- based IPC to steal the secret? Gimme your secret That’s probably not going to work
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Lecture 10 Page 6 CS 136, Winter 2010 How Can B Get the Secret? He can convince the system he’s A A problem for authentication He can break into A’s memory That doesn’t use message IPC And is handled by page tables He can forge a message from someone else to get the secret But OS tags IPC messages with identities He can “eavesdrop” on someone else who gets the secret
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Lecture 10 Page 7 CS 136, Winter 2010 Can an Attacker Really Eavesdrop on IPC Message? On a single machine, what is a message send, really? A message is copied from a process buffer to an OS buffer Then from the OS buffer to another process’ buffer Sometimes optimizations skip some copies If attacker can’t get at processes’ internal buffers and can’t get at OS buffers, he can’t “eavesdrop” Need to handle page reuse (discussed earlier)
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Lecture 10 Page 8 CS 136, Winter 2010 Other Forms of IPC Semaphores, sockets, shared memory, RPC Pretty much all the same Use system calls for access Which belong to some process Which belongs to some principal OS can check principal against access control permissions at syscall time Ultimately, data is held in some type of memory Which shouldn’t be improperly accessible
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Lecture 10 Page 9 CS 136, Winter 2010 So When Is It Hard? 1. Always possible that there’s a bug in the operating system Allowing masquerading, eavesdropping, etc. Or, if the OS itself is compromised, all bets are off 2. What if the OS has to prevent cooperating processes from sharing information?
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Lecture 10 Page 10 CS 136, Winter 2010 The Hard Case Process A Process B Process A wants to tell the secret to process B But the OS has been instructed to prevent that A necessary part of Bell-La Padula, e.g.
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