On Tue, Nov 28, 2017 at 11:48:49PM +0100, Luis R. Rodriguez wrote: > On Tue, Nov 28, 2017 at 02:18:18PM -0800, Kees Cook wrote: > > On Tue, Nov 28, 2017 at 2:12 PM, Luis R. Rodriguez <mcg...@kernel.org> > > wrote: > > > On Tue, Nov 28, 2017 at 01:39:58PM -0800, Kees Cook wrote: > > >> On Tue, Nov 28, 2017 at 1:16 PM, Luis R. Rodriguez <mcg...@kernel.org> > > >> wrote: > > >> > And *all* auto-loading uses aliases? What's the difference > > >> > between auto-loading and direct-loading? > > >> > > >> The difference is the process privileges. Unprivilged autoloading > > >> (e.g. int n_hdlc = N_HDLC; ioctl(fd, > > >> TIOCSETD, &n_hdlc)), triggers a privileged call to finit_module() > > >> under CAP_SYS_MODULE. > > > > > > Ah, so system call implicated request_module() calls. > > > > Yup. Unprivileged user does something that ultimately hits a > > request_module() in the kernel. Then the kernel calls out with the > > usermode helper (which has CAP_SYS_MODULE) and calls finit_module(). > > Thanks, using this terminology is much better to understand than > auto-loading, given it does make it clear an unprivileged call was one > that initiated the request_module() call, there are many uses of > request_module() which *are* privileged. > > > > OK and since CAP_SYS_MODULE is much more restrictive one could > > > argue, what's the point here? > > > > The goal is to block an unprivileged user from being able to trigger a > > module load without blocking root from loading modules directly. > > I see now. Do we have an audit of all system calls which implicate a > request_module() call? Networking is a good example for sure to start > off with but I was curious if we have a grasp of how wide spread this > could be.
I'm not sure it makes sense to classify this by syscalls. In networking, request_module() can be triggered e.g. by a netlink message (genetlink family lookup is an example not needing any privileges) so that one of the syscalls would be sendmsg(). Michal Kubecek
