linux-kernel - Re: [PATCH v3] usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget

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Message-ID: <2cc401dc-bfeb-402e-967e-bd1653640949@samsung.com>
Date: Fri, 9 Feb 2024 10:41:19 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-usb@...r.kernel.org"
	<linux-usb@...r.kernel.org>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>, Felipe Balbi <balbi@...nel.org>
Subject: Re: [PATCH v3] usb: dwc3: gadget: Fix NULL pointer dereference in
 dwc3_gadget_suspend

On 08.02.2024 23:54, Thinh Nguyen wrote:
> On Wed, Feb 07, 2024, Marek Szyprowski wrote:
>> On 19.01.2024 10:48, Uttkarsh Aggarwal wrote:
>>> In current scenario if Plug-out and Plug-In performed continuously
>>> there could be a chance while checking for dwc->gadget_driver in
>>> dwc3_gadget_suspend, a NULL pointer dereference may occur.
>>>
>>> Call Stack:
>>>
>>> 	CPU1:                           CPU2:
>>> 	gadget_unbind_driver            dwc3_suspend_common
>>> 	dwc3_gadget_stop                dwc3_gadget_suspend
>>>                                           dwc3_disconnect_gadget
>>>
>>> CPU1 basically clears the variable and CPU2 checks the variable.
>>> Consider CPU1 is running and right before gadget_driver is cleared
>>> and in parallel CPU2 executes dwc3_gadget_suspend where it finds
>>> dwc->gadget_driver which is not NULL and resumes execution and then
>>> CPU1 completes execution. CPU2 executes dwc3_disconnect_gadget where
>>> it checks dwc->gadget_driver is already NULL because of which the
>>> NULL pointer deference occur.
>>>
>>> Cc: <stable@...r.kernel.org>
>>> Fixes: 9772b47a4c29 ("usb: dwc3: gadget: Fix suspend/resume during device mode")
>>> Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
>>> Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
>> This patch landed some time ago in linux-next as commit 61a348857e86
>> ("usb: dwc3: gadget: Fix NULL pointer dereference in
>> dwc3_gadget_suspend"). Recently I found that it causes the following
>> warning when no USB gadget is bound to the DWC3 driver and a system
>> suspend/resume cycle is performed:
>>
>> dwc3 12400000.usb: wait for SETUP phase timed out
>> dwc3 12400000.usb: failed to set STALL on ep0out
>> ------------[ cut here ]------------
>> WARNING: CPU: 4 PID: 604 at drivers/usb/dwc3/ep0.c:289
>> dwc3_ep0_out_start+0xc8/0xcc
>> Modules linked in:
>> CPU: 4 PID: 604 Comm: rtcwake Not tainted 6.8.0-rc3-next-20240207 #7979
>> Hardware name: Samsung Exynos (Flattened Device Tree)
>>    unwind_backtrace from show_stack+0x10/0x14
>>    show_stack from dump_stack_lvl+0x58/0x70
>>    dump_stack_lvl from __warn+0x7c/0x1bc
>>    __warn from warn_slowpath_fmt+0x1a0/0x1a8
>>    warn_slowpath_fmt from dwc3_ep0_out_start+0xc8/0xcc
>>    dwc3_ep0_out_start from dwc3_gadget_soft_disconnect+0x16c/0x230
>>    dwc3_gadget_soft_disconnect from dwc3_gadget_suspend+0xc/0x90
>>    dwc3_gadget_suspend from dwc3_suspend_common+0x44/0x30c
>>    dwc3_suspend_common from dwc3_suspend+0x14/0x2c
>>    dwc3_suspend from dpm_run_callback+0x94/0x288
>>    dpm_run_callback from device_suspend+0x130/0x6d0
>>    device_suspend from dpm_suspend+0x124/0x35c
>>    dpm_suspend from dpm_suspend_start+0x64/0x6c
>>    dpm_suspend_start from suspend_devices_and_enter+0x134/0xbd8
>>    suspend_devices_and_enter from pm_suspend+0x2ec/0x380
>>    pm_suspend from state_store+0x68/0xc8
>>    state_store from kernfs_fop_write_iter+0x110/0x1d4
>>    kernfs_fop_write_iter from vfs_write+0x2e8/0x430
>>    vfs_write from ksys_write+0x5c/0xd4
>>    ksys_write from ret_fast_syscall+0x0/0x1c
>> Exception stack(0xf1421fa8 to 0xf1421ff0)
>> ...
>> irq event stamp: 14304
>> hardirqs last  enabled at (14303): [<c01a599c>] console_unlock+0x108/0x114
>> hardirqs last disabled at (14304): [<c0c229d8>]
>> _raw_spin_lock_irqsave+0x64/0x68
>> softirqs last  enabled at (13030): [<c010163c>] __do_softirq+0x318/0x4f4
>> softirqs last disabled at (13025): [<c012dd40>] __irq_exit_rcu+0x130/0x184
>> ---[ end trace 0000000000000000 ]---
>>
>> IMHO dwc3_gadget_soft_disconnect() requires some kind of a check if
>> dwc->gadget_driver is present or not, as it really makes no sense to do
> I don't think checking that is sufficient, and I don't think that's the
> case here.
>
>> any ep0 related operations if there is no gadget driver at all.
>>
> If there's indeed no gadget_driver present, then we wouldn't get this
> stack trace. (ie. dwc3_ep0_out_start should occurs when gadget_driver is
> present). This is a race happened between binding + suspend.

I have no gadget compiled into the kernel and no such created via 
configfs, so how can this be caused by a race?



> I think something like this should be sufficient. Would you mind giving
> it a try?
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 564976b3e2b9..1990d6371066 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -2656,6 +2656,11 @@ static int dwc3_gadget_soft_disconnect(struct dwc3 *dwc)
>   	int ret;
>   
>   	spin_lock_irqsave(&dwc->lock, flags);
> +	if (!dwc->pullups_connected) {
> +		spin_unlock_irqrestore(&dwc->lock, flags);
> +		return 0;
> +	}
> +
>   	dwc->connected = false;
>   
>   	/*
>
This patch fixes the reported issue. Feel free to add:

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>


Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland