linux-kernel - Re: [PATCH] usb: dwc2: gadget: don't reset gadget's driver->bus

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Message-ID: <40bf9f88-ec75-4049-412c-fd489c384205@synopsys.com>
Date:   Fri, 13 May 2022 07:18:19 +0000
From:   Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: dwc2: gadget: don't reset gadget's driver->bus

On 5/5/2022 2:46 PM, Marek Szyprowski wrote:
> UDC driver should not touch gadget's driver internals, especially it
> should not reset driver->bus. This wasn't harmful so far, but since
> commit fc274c1e9973 ("USB: gadget: Add a new bus for gadgets") gadget
> subsystem got it's own bus and messing with ->bus triggers the
> following NULL pointer dereference:
> 
> dwc2 12480000.hsotg: bound driver g_ether
> 8<--- cut here ---
> Unable to handle kernel NULL pointer dereference at virtual address 00000000
> [00000000] *pgd=00000000
> Internal error: Oops: 5 [#1] SMP ARM
> Modules linked in: ...
> CPU: 0 PID: 620 Comm: modprobe Not tainted 5.18.0-rc5-next-20220504 #11862
> Hardware name: Samsung Exynos (Flattened Device Tree)
> PC is at module_add_driver+0x44/0xe8
> LR is at sysfs_do_create_link_sd+0x84/0xe0
> ...
> Process modprobe (pid: 620, stack limit = 0x(ptrval))
> ...
>   module_add_driver from bus_add_driver+0xf4/0x1e4
>   bus_add_driver from driver_register+0x78/0x10c
>   driver_register from usb_gadget_register_driver_owner+0x40/0xb4
>   usb_gadget_register_driver_owner from do_one_initcall+0x44/0x1e0
>   do_one_initcall from do_init_module+0x44/0x1c8
>   do_init_module from load_module+0x19b8/0x1b9c
>   load_module from sys_finit_module+0xdc/0xfc
>   sys_finit_module from ret_fast_syscall+0x0/0x54
> Exception stack(0xf1771fa8 to 0xf1771ff0)
> ...
> dwc2 12480000.hsotg: new device is high-speed
> ---[ end trace 0000000000000000 ]---
> 
> Fix this by removing driver->bus entry reset.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>

Acked-by: Minas Harutyunyan <hminas@...opsys.com>

> ---
>   drivers/usb/dwc2/gadget.c | 1 -
>   1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
> index eee3504397e6..fe2a58c75861 100644
> --- a/drivers/usb/dwc2/gadget.c
> +++ b/drivers/usb/dwc2/gadget.c
> @@ -4544,7 +4544,6 @@ static int dwc2_hsotg_udc_start(struct usb_gadget *gadget,
>   
>   	WARN_ON(hsotg->driver);
>   
> -	driver->driver.bus = NULL;
>   	hsotg->driver = driver;
>   	hsotg->gadget.dev.of_node = hsotg->dev->of_node;
>   	hsotg->gadget.speed = USB_SPEED_UNKNOWN;