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

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Message-ID: <CACVXFVP5-d_1RUC+vBTLxnHZje3F1rYaJvDCgbV2-ngXfb_KNw@mail.gmail.com>
Date:	Sat, 15 Jun 2013 10:32:14 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	nirinA raseliarison <nirina.raseliarison@...il.com>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	"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 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.

Thanks,
--
Ming Lei
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