On Thu, Dec 19, 2002 at 11:35:01PM -0800, Nate Lawson wrote: > On Fri, 20 Dec 2002, Sean Kelly wrote: > > On my 5.0-CURRENT kernel built 45 minutes ago, I can bring my system to its > > knees by doing > > > > # cat /dev/io > > > > While I understand that this isn't exactly something one would normally be > > doing, is it really something that should bring the system down? > > You're running as root. So does "yes > /dev/da0" and "cat /dev/urandom > > /dev/mem" and ... (infinity)
While I don't really care to test it, I wager that `yes >/dev/da0` will not cause the system to lock hard. But you seem to be talking abot something very different. You are talking about WRITING. I am talking about READING. # cat /dev/da0 # cat /dev/urandom None of these bring the system to its knees. So why does # cat /dev/io totally lock my system solid? According to the manpage: The special file /dev/io is a controlled security hole that allows a pro- cess to gain I/O privileges (which are normally reserved for kernel- internal code). Any process that holds a file descriptor on /dev/io open will get its IOPL bits in the flag register set, thus allowing it to per- form direct I/O operations. This says nothing about what happens if you attempt to read() from /dev/io, as `cat /dev/io` would be expected to do. At the least, there should be a big, fat, blinking WARNING on the manpage telling you that `cat /dev/io` will bring your system down. -- Sean Kelly | PGP KeyID: D2E5E296 [EMAIL PROTECTED] | http://www.zombie.org
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