On Wed, Oct 26, 2016 at 07:53:44AM +0100, Robert N. M. Watson wrote: > Hi Pawel: > > In general, my strong recommendation is against issuing advisories for local > denial-of-service attacks, in part because it suggests we consider it a > security guarantee of the system that those problems can be reliably > prevented. At least in current operating-system designs, preventing local DoS > is a very hard problem (not quite up there with covert channels, but > certainly not something we can do reliably) ??? and so I think it would be > misleading to suggest to our users that they can expect them not to exist at > all. If something is being widely exploited, then it might be appropriate to > issue an errata update, but I think if it???s something obscure where a local > user to trigger a panic (and there really is no escalation path to kernel > privilege, for example), then I think an advisory would generally be a > mistake. Otherwise we???d find that a huge number of our ordinary kernel bug > fixes get reclassified as security patches requiring advisories, if nothing > else! > > (In this case, I???m not passing judgement one way or the other ??? zeroing > of arbitrary kernel memory can have more broad implications than a panic ??? > for example, you can imagine that if it were to zero a process credential, a > process might start running unexpectedly as root. And what were once thought > to be innocuous crashes due to NULL-pointer dereferences turn out not to be!)
It is not quite arbitrary kernel memory, memory is adjanced to the region allocated with kmem_malloc(kernel_arena), which puts the allocated chunk aside from the typical kernel allocations. In fact, most likely the allocated chunk is followed by an unmapped page, which means that attempt to zero past the end of legit chunk traps. In other words, I consider the escalation of the issue unlikely or, at least, hard. FWIW, I asked the same question as Pawel when initial SA was created. The answer was not technical but satisfactory. _______________________________________________ freebsd-security@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-security To unsubscribe, send any mail to "freebsd-security-unsubscr...@freebsd.org"
