linux-kernel - Re: [PATCH v2] usb: gadget: u_serial: check Null pointer in EP callback

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Message-ID: <1a81f498-f7dd-86e6-74fa-fdeefad6a7b4@quicinc.com>
Date: Tue, 20 Aug 2024 15:45:37 +0530
From: Prashanth K <quic_prashk@...cinc.com>
To: 胡连勤 <hulianqin@...o.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC: "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>,
        Michael Nazzareno Trimarchi
	<michael@...rulasolutions.com>
Subject: Re: [PATCH v2] usb: gadget: u_serial: check Null pointer in EP
 callback



On 20-08-24 02:59 pm, 胡连勤 wrote:
> From: Lianqin Hu <hulianqin@...o.com>
> 
> Added null pointer check to avoid system crash.
Address whats becoming Null and why its happening
> 
> 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>
> ---
> v2:
>   - Optimize code comments
>   - Delete log printing
> ---
>  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. */
> +	if (!port)
> +		return;
> +

This doesn't protect the port from going to NULL right after the above
the check. Since you mentioned gser_disconnect is making port to NULL,
add the serial_port_lock to protect port (just like its done on
gser_disconnect/suspend/resume). Something like this would do.

diff --git a/drivers/usb/gadget/function/u_serial.c
b/drivers/usb/gadget/function/u_serial.c
index f975dc03a190..a33f8cd871ac 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -451,10 +451,21 @@ static void gs_rx_push(struct work_struct *work)

static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
{
-       struct gs_port  *port = ep->driver_data;
+       struct gs_port  *port;
+       unsigned long   flags;
+
+       spin_lock_irqsave(&serial_port_lock, flags);
+       port = ep->driver_data;
+
+       if (!port) {
+               spin_unlock_irqrestore(&serial_port_lock, flags);
+               return;
+       }

-       /* Queue all received data until the tty layer is ready for it. */
       spin_lock(&port->port_lock);
+       spin_unlock(&serial_port_lock);
+
+       /* Queue all received data until the tty layer is ready for it. */
       list_add_tail(&req->list, &port->read_queue);
       schedule_delayed_work(&port->push, 0);
       spin_unlock(&port->port_lock);

>  	/* 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)
> +		return;
> +
>  	spin_lock(&port->port_lock);
>  	list_add(&req->list, &port->write_pool);
>  	port->write_started--;
Same here also

Best Regards,
Prashanth K