On 18.07.2017 23:04, Kees Cook wrote: > On Tue, Jul 18, 2017 at 12:56 PM, Alexander Popov <alex.popov@xxxxxxxxx> wrote: >> On 17.07.2017 22:11, Kees Cook wrote: >>> Let's merge this with the proposed CONFIG_FREELIST_HARDENED, then the >>> performance change is behind a config, and we gain the rest of the >>> freelist protections at the same time: >>> >>> http://www.openwall.com/lists/kernel-hardening/2017/07/06/1 >> >> Hello Kees, >> >> If I change BUG_ON() to VM_BUG_ON(), this check will work at least on Fedora >> since it has CONFIG_DEBUG_VM enabled. Debian based distros have this option >> disabled. Do you like that more than having this check under >> CONFIG_FREELIST_HARDENED? > > I think there are two issues: first, this should likely be under > CONFIG_FREELIST_HARDENED since Christoph hasn't wanted to make these > changes enabled by default (if I'm understanding his earlier review > comments to me). Ok, I'll rebase onto FREELIST_HARDENED and test it all together. > The second issue is what to DO when a double-free is > discovered. Is there any way to make it safe/survivable? If not, I > think it should just be BUG_ON(). If it can be made safe, then likely > a WARN_ONCE and do whatever is needed to prevent the double-free. Please correct me if I'm wrong. It seems to me that double-free is a dangerous situation that indicates some serious kernel bug (which might be maliciously exploited). So I would not trust / rely on the process which experiences a double-free error in the kernel mode. But I guess the reaction to it should depend on the Linux kernel policy of handling faults. Is it defined explicitly? Anyway, if we try to mitigate the effect from a double-free error _here_ (for example, skip putting the duplicated object to the freelist), I think we should do the same for other cases of double-free and memory corruptions. >> If you insist on putting this check under CONFIG_FREELIST_HARDENED, should I >> rebase onto your patch and send again? > > That would be preferred for me -- I'd like to have both checks. :) Ok. Best regards, Alexander -- 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>
