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> can the swap partition be used to 'spy' what happenned into a box?
>
> can someone with physical access to a box put the hard drive in
> another computer and check into the swap to find password or email or
> ...?

For the most part, any part of main memory can get swapped out at any
time. If a process that handles passwords or keys gets some or all of its
pages swapped out, then yes, you'll probablly be able retrieve those
passwords or keys from the swap disk. This is mostly only an issue with
long-running processes like ssh-agent.

You can easily verify this for yourself - write a four-line program that
allocates a buffer, sticks a constant string in it, and then sleeps
forever. Then write a program that forks a bunch of times and each copy
allocates as much memory as it can. Wait until the machine starts
thrashing, kill all the memory eaters, and then run strings(1) on your
swap partition - the constant string from the first program will almost
certainly be in there.

> what can i do about it?

There is a system call called mlock(2) which allows a program to lock its
memory pages in core, ensuring that they won't get swapped out. Security
or performance oriented programs sometimes use this. The downside is that
this call can only be made by root, so your programs have to be setuid
root. The gnupg port has some pretty generic code that provides
secure_malloc, secure_free, etc, using mlock.

Alternatively, you could arrange for your swap to be encrypted somehow
(swap to a file on a cryptfs or cfs mount) or else just not use swap.

 -Jason

 -----------------------------------------------------------------------
 I worry about my child and the Internet all the time, even though she's
 too young to have logged on yet. Here's what I worry about. I worry
 that 10 or 15 years from now, she will come to me and say "Daddy, where
 were you when they took freedom of the press away from the Internet?"
        -- Mike Godwin

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