Kyle Moffett wrote: > Please don't trim CC lists > > On Oct 11, 2007, at 17:02:37, Al Boldi wrote: > > David Newall wrote: > >> [EMAIL PROTECTED] wrote: > >>> What David meant was that "root will always have a slot" doesn't > >>> *actually* help unless you *also* have a way to actually *spawn* > >>> such a process. In order to do the ps, kill, and so on that you > >>> need to recover, you need to already have either a root shell > >>> available, or a way to *get* a root shell that doesn't rely on a > >>> non-root process (so /bin/su doesn't help here). > >> > >> That's right, although it's worse than that. You need to have a > >> process with CAP_SYS_ADMIN. If root processes normally have that > >> capability then the reserved slots may well disappear before you > >> notice a problem. If root processes normally don't have it, then > >> you need to guarantee that one is already running. > > > > I once posted a patch to handle this DoS, but, as usual, it wasn't > > accepted. Go figure... > > This isn't really necessary any more with the new CFS scheduler. If > you want to prevent excess memory usage then you limit memory usage, > not process count, so just set the system max process count to > something absurdly high and leave the user counts down at the maximum > a user might run. Then as long as the sum of the user processes is > less than the max number of processes (which you just set absurdly > high or unlimited), you may still log in. With the per-user > scheduling enabled CFS allows you to run an optimistically-real-time > game as one user and several thousand busy-loops as another user and > get almost picture perfect 50% CPU distribution between the users. > To me that seems a much better DoS-prevention system than limits > which don't scale based on how many people are requesting resources.
You have a point, and resource-controllers can probably control DoS a lot better, but the they also incur more overhead. Think of this "lockout prevention" patch as a near zero overhead safety valve. Thanks! -- Al - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
