linux-kernel - Re: [PATCH] usb: gadget: f_midi: Fixed a bug when buflen was smaller than wMaxPacketSize

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Date:	Wed, 9 Mar 2016 14:43:06 -0800
From:	Steve Calfee <stevecalfee@...il.com>
To:	"Felipe F. Tonello" <eu@...ipetonello.com>
Cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...nel.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: Re: [PATCH] usb: gadget: f_midi: Fixed a bug when buflen was smaller
 than wMaxPacketSize

On Wed, Mar 9, 2016 at 11:39 AM, Felipe F. Tonello <eu@...ipetonello.com> wrote:
> buflen by default (256) is smaller than wMaxPacketSize (512) in high-speed
> devices.
>
> That caused the OUT endpoint to freeze if the host send any data packet of
> length greater than 256 bytes.
>
> This is an example dump of what happended on that enpoint:
> HOST:   [DATA][Length=260][...]
> DEVICE: [NAK]
> HOST:   [PING]
> DEVICE: [NAK]
> HOST:   [PING]
> DEVICE: [NAK]
> ...
> HOST:   [PING]
> DEVICE: [NAK]
>
> This patch fixes this problem by setting the minimum usb_request's buffer size
> for the OUT endpoint as its wMaxPacketSize.
>
> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
> ---
>  drivers/usb/gadget/function/f_midi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
> index 8475e3dc82d4..826ba641f29d 100644
> --- a/drivers/usb/gadget/function/f_midi.c
> +++ b/drivers/usb/gadget/function/f_midi.c
> @@ -366,7 +366,9 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>         /* allocate a bunch of read buffers and queue them all at once. */
>         for (i = 0; i < midi->qlen && err == 0; i++) {
>                 struct usb_request *req =
> -                       midi_alloc_ep_req(midi->out_ep, midi->buflen);
> +                       midi_alloc_ep_req(midi->out_ep,
> +                               max_t(unsigned, midi->buflen,
> +                                       bulk_out_desc.wMaxPacketSize));
>                 if (req == NULL)
>                         return -ENOMEM;
>
Won't you get a buffer overrun if midi->buflen is less than wMaxPacketSize?

Regards, Steve