linux-kernel - Re: [PATCH 01/12] module: Move modprobe_path and modules_disabled ctl

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Message-ID: <e2ebf88d-46a2-4f38-a0c8-940c3d3bee49@suse.com>
Date: Thu, 15 May 2025 10:04:53 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Joel Granados <joel.granados@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, Kees Cook <kees@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Waiman Long <longman@...hat.com>, "Paul E. McKenney" <paulmck@...nel.org>,
 Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>, Uladzislau Rezki <urezki@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 Helge Deller <deller@....de>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>,
 linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, rcu@...r.kernel.org, linux-mm@...ck.org,
 linux-parisc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 01/12] module: Move modprobe_path and modules_disabled
 ctl_tables into the module subsys

On 5/9/25 14:54, Joel Granados wrote:
> Move module sysctl (modprobe_path and modules_disabled) out of sysctl.c
> and into the modules subsystem. Make the modprobe_path variable static
> as it no longer needs to be exported. Remove module.h from the includes
> in sysctl as it no longer uses any module exported variables.
> 
> This is part of a greater effort to move ctl tables into their
> respective subsystems which will reduce the merge conflicts in
> kernel/sysctl.c.
> 
> Signed-off-by: Joel Granados <joel.granados@...nel.org>
> [...]
> --- a/kernel/module/kmod.c
> +++ b/kernel/module/kmod.c
> @@ -60,7 +60,7 @@ static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
>  /*
>  	modprobe_path is set via /proc/sys.
>  */
> -char modprobe_path[KMOD_PATH_LEN] = CONFIG_MODPROBE_PATH;
> +static char modprobe_path[KMOD_PATH_LEN] = CONFIG_MODPROBE_PATH;
>  
>  static void free_modprobe_argv(struct subprocess_info *info)
>  {
> @@ -177,3 +177,33 @@ int __request_module(bool wait, const char *fmt, ...)
>  	return ret;
>  }
>  EXPORT_SYMBOL(__request_module);
> +
> +#ifdef CONFIG_MODULES
> +static const struct ctl_table kmod_sysctl_table[] = {
> +	{
> +		.procname	= "modprobe",
> +		.data		= &modprobe_path,
> +		.maxlen		= KMOD_PATH_LEN,
> +		.mode		= 0644,
> +		.proc_handler	= proc_dostring,
> +	},
> +	{
> +		.procname	= "modules_disabled",
> +		.data		= &modules_disabled,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		/* only handle a transition from default "0" to "1" */
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ONE,
> +		.extra2		= SYSCTL_ONE,
> +	},

This is minor.. but the file kernel/module/kmod.c contains the logic to
request direct modprobe invocation by the kernel. Registering the
modprobe_path sysctl here is appropriate. However, the modules_disabled
setting affects the entire module loader so I don't think it's best to
register it here.

I suggest keeping a single table for the module sysctl values but moving
it to kernel/module/main.c. This means the variable modprobe_path must
retain external linkage, on the other hand, modules_disabled can be made
static.

-- 
Thanks,
Petr

> +};
> +
> +static int __init init_kmod_sysctl(void)
> +{
> +	register_sysctl_init("kernel", kmod_sysctl_table);
> +	return 0;
> +}
> +
> +subsys_initcall(init_kmod_sysctl);
> +#endif