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Date: Sat, 1 Apr 2023 12:01:43 +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. 11:52, Mirsad Goran Todorovac wrote:
> 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:
Thousand apologies, the previous version had a compilation error. I've sent the untested
version.
I must have become over-confident. But they say that a mistake that makes you humbled
is better than success that makes you arrogant :-|
I would like your opinion on the patch before I actually start the kernel, for I won't
be able to reboot clean that machine if it hangs in kernel until Tuesday :-(
It seems that put_device() would call the release method of the device and kfree() in
it, but I cannot say anything about the side effects, for I do not know the source so
well ...
Kind regards,
Mirsad
---
diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c
index bf7667845459..c63250322e26 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)
+ 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?"
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