linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000040

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Message-ID: <CACVXFVPVA0N=99K7VXNcGpz6=vE+v-FcebS2iUBwo6V3zR=_og@mail.gmail.com>
Date:	Sat, 15 Jun 2013 16:08:47 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	nirinA raseliarison <nirina.raseliarison@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Francois Romieu <romieu@...zoreil.com>, nic_swsd@...ltek.com,
	Hayes Wang <hayeswang@...ltek.com>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000040

On Sat, Jun 15, 2013 at 2:30 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On Sat, Jun 15, 2013 at 10:32:14AM +0800, Ming Lei wrote:
>> On Sat, Jun 15, 2013 at 1:07 AM, nirinA raseliarison
>> <nirina.raseliarison@...il.com> wrote:
>>
>> > patch applied and no longer have the bug message when i
>> > reboot and wake up the ethernet controller.
>>
>> I am wondering if Guenter's patch can fix the race really, but I'd like to
>> see Guenter's explanation on his patch.
>>
>> The race should be caused by below:
>>
>> - request timeout triggered by internal timer
>>
>> - user space aborts the requests before the line in _request_firmware_load()
>>
>>              fw_priv->buf = NULL
>>
>> which is run in timeout path
>>
>> - then the abort() called from firmware_loading_store() may use a freed fw buf
>> since the timeout path will free the fw buffer.
>>
>> Considered clearing 'fw_priv->buf' in _request_firmware_load()() isn't protected
>> by fw_lock now, so Guenter's patch can't avoid the race entirely.
>>
> I agree; my patch only protects one specific path, and was based on the
> observation that access to fw_priv->buf is protected elsewhwere in the code.
> My suspicion was that fw_priv->buf was freed while waiting for the mutex in
> firmware_loading_store().
>
> Your patch is more comprehensive.

OK, thanks for your reply.

I will post out one version for merge, and this one moves the
"fw_priv->buf = NULL;" into fw_load_abort() for simplifying change.


Thanks,
--
Ming Lei
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