linux-kernel - Re: [PATCH 13/13] fs: move binfmt

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Message-ID: <202005290113.53AEED2176@keescook>
Date:   Fri, 29 May 2020 01:14:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     yzaikin@...gle.com, nixiaoming@...wei.com, ebiederm@...ssion.com,
        axboe@...nel.dk, clemens@...isch.de, arnd@...db.de,
        gregkh@...uxfoundation.org, jani.nikula@...ux.intel.com,
        joonas.lahtinen@...ux.intel.com, rodrigo.vivi@...el.com,
        airlied@...ux.ie, daniel@...ll.ch, benh@...nel.crashing.org,
        rdna@...com, viro@...iv.linux.org.uk, mark@...heh.com,
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        sfr@...b.auug.org.au, jack@...e.cz, amir73il@...il.com,
        rafael@...nel.org, tytso@....edu, julia.lawall@...6.fr,
        akpm@...ux-foundation.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linuxppc-dev@...ts.ozlabs.org,
        ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/13] fs: move binfmt_misc sysctl to its own file

On Fri, May 29, 2020 at 07:41:08AM +0000, Luis Chamberlain wrote:
> This moves the binfmt_misc sysctl to its own file to help remove
> clutter from kernel/sysctl.c.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  fs/binfmt_misc.c | 1 +
>  kernel/sysctl.c  | 7 -------
>  2 files changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
> index f69a043f562b..656b3f5f3bbf 100644
> --- a/fs/binfmt_misc.c
> +++ b/fs/binfmt_misc.c
> @@ -821,6 +821,7 @@ static int __init init_misc_binfmt(void)
>  	int err = register_filesystem(&bm_fs_type);
>  	if (!err)
>  		insert_binfmt(&misc_format);
> +	register_sysctl_empty_subdir("fs", "binfmt_misc");
>  	return err;

Nit: let's make the dir before registering the filesystem. I can't
imagine a realistic situation where userspace is reacting so fast it
would actually fail to mount the fs on /proc/sys/fs/binfmt_misc, but why
risk it?

-Kees

>  }
>  
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 460532cd5ac8..7714e7b476c2 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -3042,13 +3042,6 @@ static struct ctl_table fs_table[] = {
>  		.extra1		= SYSCTL_ZERO,
>  		.extra2		= SYSCTL_TWO,
>  	},
> -#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
> -	{
> -		.procname	= "binfmt_misc",
> -		.mode		= 0555,
> -		.child		= sysctl_mount_point,
> -	},
> -#endif
>  	{
>  		.procname	= "pipe-max-size",
>  		.data		= &pipe_max_size,
> -- 
> 2.26.2
> 

-- 
Kees Cook