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SubjectRe: [PATCH] usb: f_fs: Fix crash during gadget function switching
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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@allwinnertech.com>


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


--
Regards,
Michael Wu

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