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

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Date:	Sat, 16 Jan 2016 13:21:15 -0800
From:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>, "4.2+" <stable@...r.kernel.org>
Subject: Re: [PATCH RESEND] driver-core: fix modparam async_probe request

On Sat, Jan 16, 2016 at 11:05 AM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> 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.

To prevent future bugs that might use this incorrectly.

>>               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.

For the fix yes, that is true. We could split this in two. Up to Rusty.

 Luis