Re: [PATCH] usb: f_fs: Fix crash during gadget function switching

[Michael Wu]

On 5/31/2022 2:14 AM, John Keeping wrote:
> On Tue, May 10, 2022 at 04:01:05PM +0800, Michael Wu wrote:
> > On arm64 android12 and possibly other platforms, during the usb gadget
> > function switching procedure (e.g. from mtp to midi), a synchronization
> > issue could occur, which causes an use-after-free panic as shown below:
>
> I assume this is the path through ffs_epfile_io() with !io_data->aio.
> It looks like there is no check there for epfile->ep == ep which the
> other paths do check.
>
> Does the patch below fix the problem without needing to add a new
> completion?

Hi John,
Thanks for your suggestion. I've tested your patch and it did work -- 
When my issue occurs, (epfile->ep != ep) is satisfied, and the error is 
handled.

> -- >8 --
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -1084,16 +1084,22 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
>                           */
>                          usb_ep_dequeue(ep->ep, req);
>                          wait_for_completion(&done);
> -                       interrupted = ep->status < 0;
> +                       interrupted = true;
>                  }
>   
> -               if (interrupted)
> +               spin_lock_irq(&epfile->ffs->eps_lock);
> +               if (epfile->ep != ep)
> +                       ret = -ESHUTDOWN;
> +               else if (interrupted && ep->status < 0)
>                          ret = -EINTR;
> -               else if (io_data->read && ep->status > 0)
> -                       ret = __ffs_epfile_read_data(epfile, data, ep->status,
> -                                                    &io_data->data);
>                  else
>                          ret = ep->status;
> +               spin_unlock_irq(&epfile->ffs->eps_lock);
> +
> +               if (io_data->read && ret > 0)
> +                       ret = __ffs_epfile_read_data(epfile, data, ret,
> +                                                    &io_data->data);
> +
>                  goto error_mutex;
>          } else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
>                  ret = -ENOMEM;
Tested-by: Michael Wu <michael@xxxxxxxxxxxxxxxxx>


I also tested Linyu's patch [1][2]. It also works.
Is there a preference on these solutions?


[1] 
https://lore.kernel.org/linux-usb/1654056916-2062-2-git-send-email-quic_linyyuan@xxxxxxxxxxx/
[2] 
https://lore.kernel.org/linux-usb/1654056916-2062-3-git-send-email-quic_linyyuan@xxxxxxxxxxx/


--
Regards,
Michael Wu