linux-kernel - Re: BUG FIX: [PATCH RFC v3] memstick_check() memleak in kernel 6.1.0+ introduced pre 4.17

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Date:   Sat, 1 Apr 2023 11:52:59 +0200
From:   Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Maxim Levitsky <maximlevitsky@...il.com>,
        Alex Dubov <oakad@...oo.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Hannes Reinecke <hare@...e.de>,
        Jiasheng Jiang <jiasheng@...as.ac.cn>,
        ye xingchen <ye.xingchen@....com.cn>, linux-mmc@...r.kernel.org
Subject: Re: BUG FIX: [PATCH RFC v3] memstick_check() memleak in kernel 6.1.0+
 introduced pre 4.17

On 01. 04. 2023. 11:23, Greg KH wrote:
> On Sat, Apr 01, 2023 at 11:18:19AM +0200, Greg KH wrote:
>> On Sat, Apr 01, 2023 at 08:33:36AM +0200, Greg KH wrote:
>>> On Sat, Apr 01, 2023 at 08:28:07AM +0200, Greg KH wrote:
>>>> On Sat, Apr 01, 2023 at 08:23:26AM +0200, Mirsad Goran Todorovac wrote:
>>>>>> This patch is implying that anyone who calls "dev_set_name()" also has
>>>>>> to do this hack, which shouldn't be the case at all.
>>>>>>
>>>>>> thanks,
>>>>>>
>>>>>> greg k-h
>>>>>
>>>>> This is my best guess. Unless there is dev_free_name() or kobject_free_name(), I don't
>>>>> see a more sensible way to patch this up.
>>>>
>>>> In sleeping on this, I think this has to move to the driver core.  I
>>>> don't understand why we haven't seen this before, except maybe no one
>>>> has really noticed before (i.e. we haven't had good leak detection tools
>>>> that run with removable devices?)
>>>>
>>>> Anyway, let me see if I can come up with something this weekend, give me
>>>> a chance...
>>>
>>> Wait, no, this already should be handled by the kobject core, look at
>>> kobject_cleanup(), at the bottom.  So your change should be merely
>>> duplicating the logic there that already runs when the struct device is
>>> freed, right?
>>>
>>> So I don't understand why your change works, odd.  I need more coffee...
>>
>> I think you got half of the change correctly.  This init code is a maze
>> of twisty passages, let me take your patch and tweak it a bit into
>> something that I think should work.  This looks to be only a memstick
>> issue, not a driver core issue (which makes me feel better.)
> 
> Oops, forgot the patch.  Can you try this change here and let me know if
> that solves the problem or not?  I have compile-tested it only, so I
> have no idea if it works.
> 
> If this does work, I'll make up a "real" function to replace the
> horrible dev.kobj.name mess that a driver would have to do here as it
> shouldn't be required that a driver author knows the internals of the
> driver core that well...
> 
> thanks,
> 
> greg k-h
> 
> --------------------
> 
> 
> diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c
> index bf7667845459..bbfaf6536903 100644
> --- a/drivers/memstick/core/memstick.c
> +++ b/drivers/memstick/core/memstick.c
> @@ -410,6 +410,7 @@ static struct memstick_dev *memstick_alloc_card(struct memstick_host *host)
>  	return card;
>  err_out:
>  	host->card = old_card;
> +	kfree_const(card->dev.kobj.name);
>  	kfree(card);
>  	return NULL;
>  }
> @@ -468,8 +469,10 @@ static void memstick_check(struct work_struct *work)
>  				put_device(&card->dev);
>  				host->card = NULL;
>  			}
> -		} else
> +		} else {
> +			kfree_const(card->dev.kobj.name);
>  			kfree(card);
> +		}
>  	}
>  
>  out_power_off:

I thought of this version, but I am not sure about tracking the device_register() and
device_unregister() calls?

put_device() calls put_kobject() which frees the const char *kobj.name ...

I thought how host cannot just be kfree()d when host->card is still allocated.
And it is a pointer. That also seems to me like a bug :-/

Kind regards,
Mirsad

---
diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c
index bf7667845459..46c7bda9715d 100644
--- a/drivers/memstick/core/memstick.c
+++ b/drivers/memstick/core/memstick.c
@@ -179,6 +179,8 @@ static void memstick_free(struct device *dev)
 {
        struct memstick_host *host = container_of(dev, struct memstick_host,
                                                  dev);
+       if (host->card && host->card->dev)
+               put_device(&host->card->dev);
        kfree(host);
 }
 
@@ -410,7 +412,7 @@ static struct memstick_dev *memstick_alloc_card(struct memstick_host *host)
        return card;
 err_out:
        host->card = old_card;
-       kfree(card);
+       put_device(&card->dev);
        return NULL;
 }
 
@@ -468,8 +470,9 @@ static void memstick_check(struct work_struct *work)
                                put_device(&card->dev);
                                host->card = NULL;
                        }
-               } else
-                       kfree(card);
+               } else {
+                       put_device(&card->dev);
+               }
        }
 
 out_power_off:


-- 
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
 
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
The European Union

"I see something approaching fast ... Will it be friends with me?"