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 12:11:49 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
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 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?

Otherwise this seems to look good to me.

thanks,

greg k-h