linux-kernel - Re: [PATCH RESEND] driver-core: fix modparam async

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Date:	Sat, 16 Jan 2016 11:05:50 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org, hare@...e.de,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"4.2+" <stable@...r.kernel.org>
Subject: Re: [PATCH RESEND] driver-core: fix modparam async_probe request

Hi Luis,

On Fri, Jan 15, 2016 at 03:42:17PM -0800, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@...e.com>
> 
> Commit f2411da746985 ("driver-core: add driver module
> asynchronous probe support") added async probe support,
> in two forms:
> 
>   * in-kernel driver specification annotation
>   * generic async_probe module parameter (modprobe foo async_probe)
> 
> To support the generic kernel parameter parse_args() was
> extended via commit ecc8617053e0 ("module: add extra
> argument for parse_params() callback") however commit
> failed to f2411da746985 failed to add the required argument.
> 
> This causes a crash then whenever async_probe generic
> module parameter is used. This was overlooked when the
> form in which in-kernel async probe support was reworked
> a bit... Fix this as originally intended.
> 
> Cc: Hannes Reinecke <hare@...e.de>
> Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
> Cc: stable@...r.kernel.org (4.2+)
> Signed-off-by: Luis R. Rodriguez <mcgrof@...e.com>
> ---
> 
> Resending and addressing Rusty, the other patch I sent on Dec 19
> was addressed to Greg by mistake. Sorry about that.
> 
>  kernel/module.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 8f051a106676..88100ea77c55 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3402,16 +3402,22 @@ out:
>  static int unknown_module_param_cb(char *param, char *val, const char *modname,
>  				   void *arg)
>  {
> -	struct module *mod = arg;
> +	struct module *mod;
>  	int ret;
>  
>  	if (strcmp(param, "async_probe") == 0) {
> +		mod = arg;
> +		if (!mod) {
> +			ret = -ENOENT;
> +			goto out;
> +		}

Why do we need this chunk? We only call unknown_module_param_cb() from
one place and with your chunk below we do know that "mod" is never NULL.

>  		mod->async_probe_requested = true;
>  		return 0;
>  	}
>  
>  	/* Check for magic 'dyndbg' arg */
>  	ret = ddebug_dyndbg_module_param_cb(param, val, modname);
> +out:
>  	if (ret != 0)
>  		pr_warn("%s: unknown parameter '%s' ignored\n", modname, param);
>  	return 0;
> @@ -3515,7 +3521,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  
>  	/* Module is ready to execute: parsing args may do that. */
>  	after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
> -				  -32768, 32767, NULL,
> +				  -32768, 32767, mod,

I believe this is the only change that is needed.

>  				  unknown_module_param_cb);
>  	if (IS_ERR(after_dashes)) {
>  		err = PTR_ERR(after_dashes);
> -- 
> 2.6.2
> 

Thanks.

-- 
Dmitry