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Re: [PATCH v3 1/2] modules:capabilities: automatic module loading restriction

On Thu, 2017-04-20 at 00:20 +0200, Djalal Harouni wrote:
> +modules_autoload:
> +
> +A sysctl to control if modules auto-load feature is allowed or not.
> +This sysctl complements "modules_disabled" which is for all module
> +operations where this flag applies only to automatic module loading.
> +Automatic module loading happens when programs request a kernel feature
> +that is implemented by an unloaded module, the kernel automatically
> +runs the program pointed by "modprobe" sysctl in order to load the
> +corresponding module.
> +
> +When modules_autoload is set to (0), the default, there are no
> +restrictions.
> +
> +When modules_autoload is set to (1), processes must have CAP_SYS_MODULE
> +to be able to trigger a module auto-load operation, or CAP_NET_ADMIN
> +for modules with a 'netdev-%s' alias.
> +
> +When modules_autoload is set to (2), automatic module loading is
> +disabled for all. Once set, this value can not be changed.

I would expect a parameter 'modules_autoload' to be a boolean, so this
behaviour would be surprising.

What is the point of mode 2?  Why would someone want to set
modules_disabled=0 and modules_autoload=2?

> --- a/kernel/module.c
> +++ b/kernel/module.c
> +static int modules_autoload_privileged_access(const char *name)
> +{
> +	if (capable(CAP_SYS_MODULE))
> +		return 0;
> +	else if (name && strstr(name, "netdev-") && capable(CAP_NET_ADMIN))

We want a prefix match, so use strncmp() not strstr().


Ben Hutchings
It is easier to change the specification to fit the program than vice

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