On Wed 07-08-13 09:22:10, Tejun Heo wrote: > Hello, > > On Wed, Aug 07, 2013 at 01:28:25PM +0200, Michal Hocko wrote: > > There is no limit for the maximum number of threshold events registered > > per memcg. This might lead to an user triggered memory depletion if a > > regular user is allowed to register on memory.[memsw.]usage_in_bytes > > eventfd interface. > > > > Let's be more strict and cap the number of events that might be > > registered. MAX_THRESHOLD_EVENTS value is more or less random. The > > expectation is that it should be high enough to cover reasonable > > usecases while not too high to allow excessive resources consumption. > > 1024 events consume something like 16KB which shouldn't be a big deal > > and it should be good enough. > > I don't think the memory consumption per-se is the issue to be handled > here (as kernel memory consumption is a different generic problem) but > rather that all listeners, regardless of their priv level, cgroup > membership and so on, end up contributing to this single shared > contiguous table, The table is per-memcg but you are right that everybody who has file write access to the particular group's usage file can register to it. > which makes it quite easy to do DoS attack on it if > the event control is actually delegated to untrusted security domain, OK, I have obviously misunderstood your concern mentioned in the other email. Could you be more specific what is the DoS scenario which was your concern, then? [...] > Can you please update the patch description to reflect the actual > problem? As soon as I understand what is your concern ;) -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>