Re: [PATCH v1 2/2] usb: gadget: ffs: change ep->ep safe in ffs_epfile_io()

[John Keeping <john@metanate.com>]

On Tue, May 31, 2022 at 05:36:15PM +0800, Linyu Yuan wrote:
> In ffs_epfile_io(), when read/write data in blocking mode, it will wait
> the completion in interruptible mode, if task receive a signal, it will
> terminate the wait, at same time, if function unbind occurs,
> ffs_func_unbind() will kfree all eps, ffs_epfile_io() still try to
> dequeue request by dereferencing ep which may become invalid.
> 
> Fix it by add ep spinlock and will not dereference ep if it is not valid.
> 
> Signed-off-by: Linyu Yuan <quic_linyyuan@quicinc.com>

Reviewed-by: John Keeping <john@metanate.com>

> ---
>  drivers/usb/gadget/function/f_fs.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index dcba835..b6c9b44 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -1077,6 +1077,11 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
>  		spin_unlock_irq(&epfile->ffs->eps_lock);
>  
>  		if (wait_for_completion_interruptible(&io_data->done)) {
> +			spin_lock_irq(&epfile->ffs->eps_lock);
> +			if (epfile->ep != ep) {
> +				ret = -ESHUTDOWN;
> +				goto error_lock;
> +			}
>  			/*
>  			 * To avoid race condition with ffs_epfile_io_complete,
>  			 * dequeue the request first then check
> @@ -1084,6 +1089,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
>  			 * condition with req->complete callback.
>  			 */
>  			usb_ep_dequeue(ep->ep, req);
> +			spin_unlock_irq(&epfile->ffs->eps_lock);
>  			wait_for_completion(&io_data->done);
>  			interrupted = true;
>  		}
> -- 
> 2.7.4
>