Messages in this thread | | | From | (Alan Cox) | Subject | Re: kill -9 <pid of X> | Date | Wed, 12 Aug 1998 21:26:34 +0100 (BST) |
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> Remember, we're talking about defending against signals from a hostile > root who wants to crash the video card. In this scenario, not even the > kernel can do it -- root can install a kernel module which overwrites
Signals are the uninteresting end of the problem, being root is uninteresting. The bigger problems are that X11 is subject to being killed with sig 9 (which with a horrible kernel hack can be blocked for iopl3 processes)
Now you need the signal 9 blocking hack because any parent process that sits around to catch X failures does _not_ know the exact state of the video card.
The related problems are SAK - which is defined to kill all processes on that VT and out of resource kills from the kernel (oom()). SAK is not that big a deal - a setuid "sak signal" ioctl akin to the way you take over console switching covers it. Oom is trickier.
> Boy, it's no wonder Linus is grumpy these days.
Being grumpy and being right are different things.
I'd agree however - you don't need to put all mode switching code in kernel if you allow iopl3 proceses to lock out sig 9 and you provide a sak hook. Oom should be solvable its just harder
Alan
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