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'll go review the patches again now with all this in mind. Luis
