On Fri, 2011-03-04 at 09:48 -0800, Linus Torvalds wrote: > On Fri, Mar 4, 2011 at 9:36 AM, Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote: > > > > We need to either keep the bad guys away from the counts (this patch), > > or de-correlate the counts moving around with the position of objects in > > the slab. Ted's suggestion is a good one, and the only other thing I > > can think of is to make the values useless, perhaps by batching and > > delaying the (exposed) counts by a random amount. > > We might just decide to expose the 'active' count for regular users > (and then, in case there are tools there that parse this as normal > users, we could set the 'total' fields to be the same as the active > one, possibly rounded up to the slab allocation or something. > > I know, I know, from a memory usage standpoint, 'active' is secondary, > but it still correlates fairly well, so it's still useful. And for > seeing memory leaks (as opposed to slab fragmentation etc issues), > it's actually the interesting case. > > And at the same time, it's actually much less involved with actual > physical allocations than 'total' is, and thus much less of an attack > vector. The fact that we got another socket allocation when we opened > a new socket is not "useful" information for an attacker, not in the > way it is to see a hint of _where_ the socket got allocated. > > Of course, as you say, '/proc/meminfo' still does give you the trigger > for "oh, now somebody actually allocated a new page". That's totally > independent of slabinfo, though (and knowing the number of active > slabs would neither help nor hurt somebody who uses meminfo - you > might as well allocate new sockets in a loop, and use _only_ meminfo > to see when that allocated a new page). I think lying to the user is much worse than changing the permissions. The cost of the resulting confusion is WAY higher. -- Mathematics is the supreme nostalgia of our time. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>