[OLPC Security] Securing the laptop: DoS

Simson L. Garfinkel simsong at acm.org
Sat Oct 7 22:40:51 EDT 2006


This is pretty easy to defeat: just bust the cache so that the system 
doesn't know the difference between data that's going to be overwritten 
and data that isn't.
Hell, use a PNG so that the system can't tell the difference.
And if you buffer writes to RAM, you lose a lot of reliability. What 
happens if the machine is turned off before the buffers flush?


John Moser wrote:
> ! The onboard NAND flash has a limited number of writes per sector
>   before it will start to wear out. JFFS2 tries its best to mitigate
>   repeated writes to a file by distributing the writes evenly over the
>   whole flash chip.
>   * Opening a file and running a {modify, fsync} endless loop on it
>     should be able to kill the flash chip in minutes
>
>
> ^^^ This is probably the easiest to handle.  Just buffer and delay
> writes for a good 30-45 seconds, merging the changes in memory and then
> snapshotting and writing back to disk.  This will take some amount of
> code to get done, but doesn't such code already exist anyway?
> (laptop mode...)
>
>   



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