Re: [PATCH] usblp: fix race between disconnect() and read()

[Greg KH <gregKH@linuxfoundation.org>]

On Thu, Sep 17, 2020 at 12:34:27PM +0200, Oliver Neukum wrote:
> read() needs to check whether the device has been
> disconnected before it tries to talk to the device.
> 
> Signed-off-by: Oliver Neukum <oneukum@suse.com>
> Reported-by: syzbot+be5b5f86a162a6c281e6@syzkaller.appspotmail.com
> ---
>  drivers/usb/class/usblp.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c
> index 084c48c5848f..67cbd42421be 100644
> --- a/drivers/usb/class/usblp.c
> +++ b/drivers/usb/class/usblp.c
> @@ -827,6 +827,11 @@ static ssize_t usblp_read(struct file *file, char __user *buffer, size_t len, lo
>  	if (rv < 0)
>  		return rv;
>  
> +	if (!usblp->present) {
> +		count = -ENODEV;
> +		goto done;
> +	}
> +

What prevents ->present from not being changed right after this test?

thanks,

greg k-h