Re: Per-process flag set via prctl() to deny module loading?

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On 10.4.2023 16.36, Tycho Andersen wrote:
On Mon, Apr 10, 2023 at 01:06:00PM +0300, Topi Miettinen wrote:
I'd propose to add a per-process flag to irrevocably deny any loading of
kernel modules for the process and its children. The flag could be set (but
not unset) via prctl() and for unprivileged processes, only when
NoNewPrivileges is also set. This would be similar to CAP_SYS_MODULE, but
unlike capabilities, there would be no issues with namespaces since the flag
isn't namespaced.

The implementation should be very simple.

Preferably the flag, when configured, would be set by systemd, Firejail and
maybe also container managers. The expectation would be that the permission
to load modules would be retained only by udev and where SUID needs to be
allowed (NoNewPrivileges unset).

You can do something like this today via STATIC_USERMODEHELPER without
the need for kernel patches. It is a bit heavyweight for a
general-purpose system though.

So the user mode helper would be launched whenever there is a module request and it would check whether the process is allowed to load modules or not? Does it know which process caused the module to be loaded and what were its credentials at that time?


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