r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

[Greg Kroah-Hartman]

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@gmail.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?

Otherwise this seems to look good to me.

thanks,

greg k-h

r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

[Jia-Ju Bai]

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@gmail.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

r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

[Jia-Ju Bai]

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@gmail.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);
 	if (pipenum == 0) {
 		kfree(hep->hcpriv);
 		hep->hcpriv = NULL;
+		spin_unlock_irqrestore(&r8a66597->lock, flags);
 		return;
 	}
 
-	spin_lock_irqsave(&r8a66597->lock, flags);
 	pipe_stop(r8a66597, pipe);
 	pipe_irq_disable(r8a66597, pipenum);
 	disable_irq_empty(r8a66597, pipenum);