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

[Thinh Nguyen]

On Wed, Feb 07, 2024, Marek Szyprowski wrote:
> Dear All,
> 
> 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@xxxxxxxxxxxxxxx>
> > Fixes: 9772b47a4c29 ("usb: dwc3: gadget: Fix suspend/resume during device mode")
> > Acked-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> > Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@xxxxxxxxxxx>
> 
> 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 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;
 
 	/*


Thanks,
Thinh