Re: [PATCH v3] usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget_suspend

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

Sorry for the late reply.

On Fri, Feb 09, 2024, Marek Szyprowski wrote:
> 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@vger.kernel.org>
> >>> Fixes: 9772b47a4c29 ("usb: dwc3: gadget: Fix suspend/resume during device mode")
> >>> Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> >>> Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@quicinc.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?

Ah... In that case, we got through the incomplete/wrong check for
dwc3_gadget_soft_disconnect():
	if (dwc->ep0state != EP0_SETUP_PHASE)

Since there's no gadget driver, the controller never started and the
ep0state is defaulted to EP0_UNCONNECTED, which explained why it got
into the timeout condition above and incorrectly attempt to start the
control transfer.

> 
> 
> 
> > 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@samsung.com>
> 

Thanks for the report and Tested-by! I'll send a fix patch soon.

BR,
Thinh