linux-kernel - Re: [PATCH] r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint

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Date:   Tue, 18 Dec 2018 19:53:56 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] r8a66597: Fix a possible concurrency use-after-free bug
 in r8a66597_endpoint_disable()



On 2018/12/18 19:11, Greg KH wrote:
> On Tue, Dec 18, 2018 at 06:00:20PM +0800, Jia-Ju Bai wrote:
>> The function r8a66597_endpoint_disable() and r8a66597_urb_enqueue() may
>> be concurrently executed.
>> The two functions both access a possible shared variable "hep->hcpriv".
>>
>> This shared variable is freed by r8a66597_endpoint_disable() via the
>> call path:
>> r8a66597_endpoint_disable
>>    kfree(hep->hcpriv) (line 1995 in Linux-4.19)
>>
>> This variable is read by r8a66597_urb_enqueue() via the call path:
>> r8a66597_urb_enqueue
>>    spin_lock_irqsave(&r8a66597->lock);
>>    init_pipe_info
>>      enable_r8a66597_pipe
>>        pipe = hep->hcpriv (line 802 in Linux-4.19)
>>
>> The read operation is protected by a spinlock, but the free operation
>> is not protected by this spinlock, thus a concurrency use-after-free bug
>> may occur.
>>
>> To fix this bug, the spin-lock and spin-unlock function calls in
>> r8a66597_endpoint_disable() are moved to protect the free operation.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> ---
>>   drivers/usb/host/r8a66597-hcd.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/host/r8a66597-hcd.c b/drivers/usb/host/r8a66597-hcd.c
>> index 984892dd72f5..1495ce14ad22 100644
>> --- a/drivers/usb/host/r8a66597-hcd.c
>> +++ b/drivers/usb/host/r8a66597-hcd.c
>> @@ -1991,13 +1991,14 @@ static void r8a66597_endpoint_disable(struct usb_hcd *hcd,
>>   		return;
>>   	pipenum = pipe->info.pipenum;
>>   
>> +	spin_lock_irqsave(&r8a66597->lock, flags);
> Don't you also need the __aquires/__releases markings on this function
> in order to properly annotate it, like the rest of the driver has?

Okay, thanks for this suggestion :)
I will send a v2 patch.


Best wishes,
Jia-Ju Bai