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:

quoted

On Tue, Nov 28, 2017 at 2:12 PM, Luis R. Rodriguez [off-list ref] wrote:

quoted

On Tue, Nov 28, 2017 at 01:39:58PM -0800, Kees Cook wrote:

quoted

On Tue, Nov 28, 2017 at 1:16 PM, Luis R. Rodriguez [off-list ref] wrote:

quoted

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.

quoted

quoted

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
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