linux-kernel - Re: [RFC] export module parameters even the permission is zero

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Date:	Tue, 20 Jan 2015 17:02:39 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Wang\, Yalin" <Yalin.Wang@...ymobile.com>,
	"'akpm\@linux-foundation.org'" <akpm@...ux-foundation.org>,
	"'jani.nikula\@intel.com'" <jani.nikula@...el.com>,
	"'hch\@infradead.org'" <hch@...radead.org>,
	"'hare\@suse.de'" <hare@...e.de>,
	"'keescook\@chromium.org'" <keescook@...omium.org>,
	"'linux-kernel\@vger.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] export module parameters even the permission is zero

"Wang, Yalin" <Yalin.Wang@...ymobile.com> writes:
> This patch make sure to export module parameters even the permission
> is zero, this is useful for some platforms like Android,
> the init process can change the parameter mode/owner by
> chmod/chown during bootup
>
> Signed-off-by: Yalin Wang <yalin.wang@...ymobile.com>

Hi!

        Unfortunately, this won't work.  Various parts of the code
assume that 0 permissions means "cannot be changed or read", so this
change would introduce many bugs (eg. the parameter could be
__initdata).

Since these are owned by root at boot, changing mode and owner should
still work.  However, you can't make a read-only field writable and
expect it to work.

Hope that helps,
Rusty.



> ---
>  kernel/params.c | 6 ------
>  1 file changed, 6 deletions(-)
>
> diff --git a/kernel/params.c b/kernel/params.c
> index bd65d136..aa80c04 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -607,9 +607,6 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
>  	struct attribute **new_attrs;
>  	unsigned int i;
>  
> -	/* We don't bother calling this with invisible parameters. */
> -	BUG_ON(!kp->perm);
> -
>  	if (!mk->mp) {
>  		/* First allocation. */
>  		mk->mp = kzalloc(sizeof(*mk->mp), GFP_KERNEL);
> @@ -812,9 +809,6 @@ static void __init param_sysfs_builtin(void)
>  	for (kp = __start___param; kp < __stop___param; kp++) {
>  		char *dot;
>  
> -		if (kp->perm == 0)
> -			continue;
> -
>  		dot = strchr(kp->name, '.');
>  		if (!dot) {
>  			/* This happens for core_param() */
> -- 
> 2.1.3
> --
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