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

[Kees Cook]

On Tue, Nov 28, 2017 at 1:16 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> 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.

>> 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