On Thu, 2011-09-29 at 20:18 +0400, Vasiliy Kulikov wrote: > I'm not convinced with rounding the information to MBs. The attacker > still may fill slabs with new objects to trigger new slab pages > allocations. He will be able to see when this MB-granularity barrier is > overrun thus seeing how many kbs there were before: > > old = new - filled_obj_size_sum > > As `new' is just increased, it means it is known with KB granularity, > not MB. By counting used slab objects he learns filled_obj_size_sum. > > So, rounding gives us nothing, but obscurity. I'll agree that it doesn't fundamentally fix anything. But, it does make an attack more difficult in the real world. There's a reason that real-world attackers are going after slabinfo: it's a fundamentally *BETTER* than meminfo as a tool with which to aim an attack. A MB-rounded meminfo is also fundamentally *BETTER* than a PAGE_SIZE-rounded meminfo. I find it hard to call this "nothing". Anyway... I'm working on a patch. Will post soon. -- Dave -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>