linux-kernel - Re: [PATCH -next] watchdog: Fix possible use-after-free by calling del_timer

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Message-ID: <a7e5baa5-519f-cc55-42aa-affa6c72c530@huawei.com>
Date:   Thu, 13 May 2021 10:01:35 +0800
From:   Samuel Zou <zou_wei@...wei.com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     <wim@...ux-watchdog.org>, <vz@...ia.com>,
        <linux-watchdog@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] watchdog: Fix possible use-after-free by calling
 del_timer_sync()

Hi Guenter,

Thanks for your review. If there are similar issues in the future, I 
will collect them together and submit as one patch.

On 2021/5/12 22:06, Guenter Roeck wrote:
> On Wed, May 12, 2021 at 02:57:56PM +0800, Zou Wei wrote:
>> This driver's remove path calls del_timer(). However, that function
>> does not wait until the timer handler finishes. This means that the
>> timer handler may still be running after the driver's remove function
>> has finished, which would result in a use-after-free.
>>
>> Fix by calling del_timer_sync(), which makes sure the timer handler
>> has finished, and unable to re-schedule itself.
>>
>> Reported-by: Hulk Robot <hulkci@...wei.com>
>> Signed-off-by: Zou Wei <zou_wei@...wei.com>
> 
> If you have more of those, _please_ submit them together to save review time.
> 
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> 
> Guenter
> >> ---
>>   drivers/watchdog/lpc18xx_wdt.c | 2 +-
>>   drivers/watchdog/w83877f_wdt.c | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/watchdog/lpc18xx_wdt.c b/drivers/watchdog/lpc18xx_wdt.c
>> index 78cf11c..60b6d74 100644
>> --- a/drivers/watchdog/lpc18xx_wdt.c
>> +++ b/drivers/watchdog/lpc18xx_wdt.c
>> @@ -292,7 +292,7 @@ static int lpc18xx_wdt_remove(struct platform_device *pdev)
>>   	struct lpc18xx_wdt_dev *lpc18xx_wdt = platform_get_drvdata(pdev);
>>   
>>   	dev_warn(&pdev->dev, "I quit now, hardware will probably reboot!\n");
>> -	del_timer(&lpc18xx_wdt->timer);
>> +	del_timer_sync(&lpc18xx_wdt->timer);
>>   
>>   	return 0;
>>   }
>> diff --git a/drivers/watchdog/w83877f_wdt.c b/drivers/watchdog/w83877f_wdt.c
>> index 5772cc5..f265086 100644
>> --- a/drivers/watchdog/w83877f_wdt.c
>> +++ b/drivers/watchdog/w83877f_wdt.c
>> @@ -166,7 +166,7 @@ static void wdt_startup(void)
>>   static void wdt_turnoff(void)
>>   {
>>   	/* Stop the timer */
>> -	del_timer(&timer);
>> +	del_timer_sync(&timer);
>>   
>>   	wdt_change(WDT_DISABLE);
>>   
>> -- 
>> 2.6.2
>>
> .
>