Re: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap()

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

quoted

We already have a global sysctl for blocking direct-loading (modules_disabled).

My point was that even if you have a CAP_NET_ADMIN check on request_module(),
finit_module() will not check for it, so a crafty userspace could still try
to just finit_module() directly, and completely then bypass the CAP_NET_ADMIN
check.

You need CAP_SYS_MODULE to run finit_module().

-Kees

-- 
Kees Cook
Pixel Security