linux-kernel - Re: [PATCH] usb: musb: fix crash with highmen PIO and usbmon

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Date:   Mon, 9 Mar 2020 09:01:06 -0500
From:   Bin Liu <b-liu@...com>
To:     Mans Rullgard <mans@...sr.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: musb: fix crash with highmen PIO and usbmon

Hi Mans,

On Sat, Mar 07, 2020 at 01:07:20PM +0000, Mans Rullgard wrote:
> When handling a PIO bulk transfer with highmem buffer, a temporary
> mapping is assigned to urb->transfer_buffer.  After the transfer is
> complete, an invalid address is left behind in this pointer.  This is
> not ordinarily a problem since nothing touches that buffer before the
> urb is released.  However, when usbmon is active, usbmon_urb_complete()
> calls (indirectly) mon_bin_get_data() which does access the transfer
> buffer if it is set.  To prevent an invalid memory access here, reset
> urb->tranfer_buffer to NULL when finished.
> 
> Fixes: 8e8a55165469 ("usb: musb: host: Handle highmem in PIO mode")
> Signed-off-by: Mans Rullgard <mans@...sr.com>

Thanks for fixing the bug.

> ---
>  drivers/usb/musb/musb_host.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
> index 1c813c37462a..b67b40de1947 100644
> --- a/drivers/usb/musb/musb_host.c
> +++ b/drivers/usb/musb/musb_host.c
> @@ -1459,8 +1459,10 @@ void musb_host_tx(struct musb *musb, u8 epnum)
>  	qh->segsize = length;
>  
>  	if (qh->use_sg) {
> -		if (offset + length >= urb->transfer_buffer_length)
> +		if (offset + length >= urb->transfer_buffer_length) {
>  			qh->use_sg = false;
> +			urb->transfer_buffer = NULL;
> +		}

In this tx case, can you directly pass qh->sg_miter.addr to
musb_write_fifo() so that urb->transfer_buffer is not touched at all?

-Bin.