On Wed, Oct 3, 2012 at 11:02 AM, David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Wed, 3 Oct 2012, Kees Cook wrote: > >> > So root does echo 0 > /proc/sys/kernel/kptr_restrict first. Again: what >> > are you trying to protect? >> >> Only CAP_SYS_ADMIN can change the setting. This is, for example, for >> containers, or other situations where a uid 0 process lacking >> CAP_SYS_ADMIN cannot see virtual addresses. It's a very paranoid case, >> yes, but it's part of how this feature was designed. Think of it as >> supporting the recent uid 0 vs ring 0 boundary. :) >> > > The intention of /proc/vmallocinfo being S_IRUSR is obviously to only > allow root to read this information to begin with, so if root lacks > CAP_SYS_ADMIN then it seems the best fix would be to return an empty file > on read()? Or give permission to everybody to read it but only return a > positive count when they have CAP_SYS_ADMIN? > > There's no need to make this so convoluted that you need to have the right > combination of uid, kptr_restrict, CAP_SYS_ADMIN, and CAP_SYSLOG to get > anything valuable out of this file, though. Well, the existing mechanism is using %pK. I see no reason to add additional complexity. -Kees -- Kees Cook Chrome OS Security -- 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>