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

[Marek Szyprowski <m.szyprowski@samsung.com>]

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@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 
any ep0 related operations if there is no gadget driver at all.


> ---
>
> changes in v3:
> Corrected fixes tag and typo mistake in commit message dw3_gadget_stop -> dwc3_gadget_stop.
>
> Link to v2:
> https://lore.kernel.org/linux-usb/CAKzKK0r8RUqgXy1o5dndU21KuTKtyZ5rn5Fb9sZqTPZqAjT_9A@mail.gmail.com/T/#t
>
> Changes in v2:
> Added cc and fixes tag missing in v1.
>
> Link to v1:
> https://lore.kernel.org/linux-usb/20240110095532.4776-1-quic_uaggarwa@quicinc.com/T/#u
>
>   drivers/usb/dwc3/gadget.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 019368f8e9c4..564976b3e2b9 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -4709,15 +4709,13 @@ int dwc3_gadget_suspend(struct dwc3 *dwc)
>   	unsigned long flags;
>   	int ret;
>   
> -	if (!dwc->gadget_driver)
> -		return 0;
> -
>   	ret = dwc3_gadget_soft_disconnect(dwc);
>   	if (ret)
>   		goto err;
>   
>   	spin_lock_irqsave(&dwc->lock, flags);
> -	dwc3_disconnect_gadget(dwc);
> +	if (dwc->gadget_driver)
> +		dwc3_disconnect_gadget(dwc);
>   	spin_unlock_irqrestore(&dwc->lock, flags);
>   
>   	return 0;

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