linux-kernel - Re: [PATCH] usb: gadget: f_fs: Fix kernel panic for SuperSpeed

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Date:	Mon, 25 Apr 2016 19:32:40 +0800
From:	Jim Lin <jilin@...dia.com>
To:	Felipe Balbi <balbi@...nel.org>
CC:	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: f_fs: Fix kernel panic for SuperSpeed

On 2016年04月22日 19:52, Felipe Balbi wrote:
> * PGP Signed by an unknown key
>
>
> Hi Jim,
>
> Jim Lin <jilin@...dia.com> writes:
>> Android N adds os_desc_compat in v2_descriptor by init_functionfs()
>> (system/core/adb/usb_linux_client.cpp) to support automatic install
>> of MTP driver on Windows for USB device mode.
>>
>> Current __ffs_data_do_os_desc() of f_fs.c will check reserved1 field
>> and return -EINVAL.
>> This results in a second adb_write of usb_linux_client.cpp
>> (system/core/adb/) which doesn't have ss_descriptors filled.
>> Then later kernel_panic (composite.c) occurs when ss_descriptors
>> as a pointer with NULL is being accessed.
> where exactly in composite.c are we dereferencing a NULL pointer ?
In set_config

for (; *descriptors; ++descriptors) {



Here is the link which shows reserved (at offset 1, e.g., Function 
Section 2) as  1.
https://msdn.microsoft.com/en-us/library/windows/hardware/gg463179.aspx


>
> Is this happening on set_config() ? If that's the case, why is
> gadget->speed set to USB_SPEED_SUPER to start with ? Your controller
> should already have negotiated highspeed which means
> function_descriptors() should have returned highspeed descriptors, not a
> NULL superspeed.
>
> Care to explain why you haven't negotiated Highspeed ? The only thing I
> can think of is that you're using a Superspeed-capable peripheral
> controller (dwc3?) with maximum-speed set to Superspeed, with a
> Superspeed-capable cable connected to an XHCI PC, but loading a
> high-speed gadget driver (which you got from Android, written with f_fs)
> and this gadget doesn't tell composite that its maximum speed is
> Highspeed, instead of super-speed.
>
> We can add a check, sure, to avoid a kernel oops; however, you should
> really fix up the gadget implementation and/or set dwc3's maximum-speed
> property accordingly.
>
> Can you check if this patch makes your scenario work while still being
> fully functional ?
>
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index de9ffd60fcfa..3d3cdc5ed20d 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -66,20 +66,36 @@ function_descriptors(struct usb_function *f,
>   {
>   	struct usb_descriptor_header **descriptors;
>   
> +	/*
> +	 * NOTE: we try to help gadget drivers which might not be setting
> +	 * max_speed appropriately.
> +	 */
> +
>   	switch (speed) {
>   	case USB_SPEED_SUPER_PLUS:
>   		descriptors = f->ssp_descriptors;
> -		break;
> +		if (descriptors)
> +			break;
> +		/* FALLTHROUGH */
>   	case USB_SPEED_SUPER:
>   		descriptors = f->ss_descriptors;
> -		break;
> +		if (descriptors)
> +			break;
> +		/* FALLTHROUGH */
>   	case USB_SPEED_HIGH:
>   		descriptors = f->hs_descriptors;
> -		break;
> +		if (descriptors)
> +			break;
> +		/* FALLTHROUGH */
>   	default:
>   		descriptors = f->fs_descriptors;
>   	}
>   
> +	/*
> +	 * if we can't find any descriptors at all, then this gadget deserves to
> +	 * Oops with a NULL pointer dereference
> +	 */
> +
>   	return descriptors;
>   }
>   
After trying your change, no kernel panic, but SuperSpeed device (device 
mode) is not enumerated by ubuntu 14.04 USB 3.0 host controller as MTP 
device with USB3.0 cable.

--nvpublic