linux-kernel - Re: [PATCH] usb: interface: allow drivers declare number of endpoints they need

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Message-ID: <87y4df180w.fsf@saruman.tx.rr.com>
Date:	Mon, 30 Nov 2015 15:39:43 -0600
From:	Felipe Balbi <balbi@...com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Vladis Dronov <vdronov@...hat.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: interface: allow drivers declare number of endpoints they need


Hi,

Dmitry Torokhov <dmitry.torokhov@...il.com> writes:
> USB interface drivers need to check number of endpoints before trying to
> access/use them. Quite a few drivers only use the default setting
> (altsetting 0), so let's allow them to declare number of endpoints in
> altsetting 0 they require to operate and have USB core check it for us
> instead of having every driver implement check manually.
>
> For compatibility, if driver does not specify number of endpoints (i.e.
> number of endpoints is left at 0) we bypass the check in USB core and
> expect the driver perform necessary checks on its own.
>
> Acked-by: Alan Stern <stern@...land.harvard.edu>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>
> Greg, if the patch is reasonable I wonder if I can take it through my
> tree, as I have a few drivers that do not check number of endpoints
> properly and will crash the kernel when specially crafted device is
> plugged in, as reported by Vladis Dronov.
>
>  drivers/usb/core/driver.c | 9 +++++++++
>  include/linux/usb.h       | 7 +++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index 6b5063e..d9f680d 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -306,6 +306,15 @@ static int usb_probe_interface(struct device *dev)
>  
>  	dev_dbg(dev, "%s - got id\n", __func__);
>  
> +	if (driver->num_endpoints &&

this part of the check is pointless, right ?

> +	    intf->altsetting[0].desc.bNumEndpoints < driver->num_endpoints) {

bNumEndpoints will never be less than 0 and if it is, we're gonna have
issues elsewhere anyway.

-- 
balbi

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