linux-kernel - Re: [PATCH] usb: gadget: u_serial: check Null pointer in EP callback

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Message-ID: <2024081635-slacking-buzz-acce@gregkh>
Date: Fri, 16 Aug 2024 13:01:02 +0200
From: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To: 胡连勤 <hulianqin@...o.com>
Cc: "quic_prashk@...cinc.com" <quic_prashk@...cinc.com>,
	"quic_jjohnson@...cinc.com" <quic_jjohnson@...cinc.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"opensource.kernel" <opensource.kernel@...o.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] usb: gadget: u_serial: check Null pointer in EP callback

On Fri, Aug 16, 2024 at 10:49:19AM +0000, 胡连勤 wrote:
> From: Lianqin Hu <hulianqin@...o.com>
> 
> Added null pointer check to avoid system crash.
> 
> Unable to handle kernel NULL pointer dereference at
> virtual address 00000000000001a8
> pc : gs_read_complete+0x58/0x240
> lr : usb_gadget_giveback_request+0x40/0x160
> sp : ffffffc00f1539c0
> x29: ffffffc00f1539c0 x28: ffffff8002a30000 x27: 0000000000000000
> x26: ffffff8002a30000 x25: 0000000000000000 x24: ffffff8002a30000
> x23: ffffff8002ff9a70 x22: ffffff898e7a7b00 x21: ffffff803c9af9d8
> x20: ffffff898e7a7b00 x19: 00000000000001a8 x18: ffffffc0099fd098
> x17: 0000000000001000 x16: 0000000080000000 x15: 0000000ac1200000
> x14: 0000000000000003 x13: 000000000000d5e8 x12: 0000000355c314ac
> x11: 0000000000000015 x10: 0000000000000012 x9 : 0000000000000008
> x8 : 0000000000000000 x7 : 0000000000000000 x6 : ffffff887cd12000
> x5 : 0000000000000002 x4 : ffffffc00f9b07f0 x3 : ffffffc00f1538d0
> x2 : 0000000000000001 x1 : 0000000000000000 x0 : 00000000000001a8
> Call trace:
> gs_read_complete+0x58/0x240
> usb_gadget_giveback_request+0x40/0x160
> dwc3_remove_requests+0x170/0x484
> dwc3_ep0_out_start+0xb0/0x1d4
> __dwc3_gadget_start+0x25c/0x720
> kretprobe_trampoline.cfi_jt+0x0/0x8
> kretprobe_trampoline.cfi_jt+0x0/0x8
> udc_bind_to_driver+0x1d8/0x300
> usb_gadget_probe_driver+0xa8/0x1dc
> gadget_dev_desc_UDC_store+0x13c/0x188
> configfs_write_iter+0x160/0x1f4
> vfs_write+0x2d0/0x40c
> ksys_write+0x7c/0xf0
> __arm64_sys_write+0x20/0x30
> invoke_syscall+0x60/0x150
> el0_svc_common+0x8c/0xf8
> do_el0_svc+0x28/0xa0
> el0_svc+0x24/0x84
> el0t_64_sync_handler+0x88/0xec
> el0t_64_sync+0x1b4/0x1b8
> Code: aa1f03e1 aa1303e0 52800022 2a0103e8 (88e87e62)
> ---[ end trace 938847327a739172 ]---
> Kernel panic - not syncing: Oops: Fatal exception
> 
> Signed-off-by: Lianqin Hu <hulianqin@...o.com>
> ---
>  drivers/usb/gadget/function/u_serial.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index b394105e55d6..65637d53bf02
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -454,6 +454,14 @@ static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
>  {
>  	struct gs_port	*port = ep->driver_data;
>  
> +	/*
> +	 * When port is NULL, Return to avoid panic.
> +	 */

Multiple line comments for something like this really isn't needed.

> +	if (!port) {
> +		pr_err("%s, failed to get port\n", __func__);

No need for this either, right?

But how can this happen?  What is causing driver_data to be NULL?  And
what protects it from happening right after you check for it?

> +		return;
> +	}
> +
>  	/* Queue all received data until the tty layer is ready for it. */
>  	spin_lock(&port->port_lock);
>  	list_add_tail(&req->list, &port->read_queue);
> @@ -465,6 +473,14 @@ static void gs_write_complete(struct usb_ep *ep, struct usb_request *req)
>  {
>  	struct gs_port	*port = ep->driver_data;
>  
> +	/*
> +	 * When port is NULL, Return to avoid panic.
> +	 */
> +	if (!port) {
> +		pr_err("%s, failed to get port\n", __func__);
> +		return;
> +	}

Same question here, what is keeping it from changing right after you
test?

thanks,

greg k-h