[PATCH v6] usb: gadget: u_serial: Add null pointer check in gs_read_complete & gs_write_complete

[胡连勤 <hulianqin@xxxxxxxx>]

From: Lianqin Hu <hulianqin@xxxxxxxx>

Considering that in some extreme cases, when the unbind operation
is being executed, gserial_disconnect has already cleared gser->ioport,
and the controller has not stopped & pullup 0, sys.usb.config is reset
and the bind operation will be re-executed, calling gs_read_complete,
which will result in accessing gser->iport, resulting in a null pointer
dereference, add a null pointer check to prevent this situation.

Added a static spinlock to prevent gser->ioport from becoming
null after the newly added check.

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

Fixes: c1dca562be8a ("usb gadget: split out serial core")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lianqin Hu <hulianqin@xxxxxxxx>
---
v6:
  - Update the commit text
  - Add the Fixes tag
  - CC stable kernel
  - Add serial_port_lock protection when checking port pointer
  - Optimize code comments
  - Delete log printing
---
 drivers/usb/gadget/function/u_serial.c | 33 ++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index b394105e55d6..e43d8065f7ec 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -452,20 +452,43 @@ 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;
+
+	/* When port is NULL, return to avoid panic. */
+	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);
+	spin_unlock_irqrestore(&port->port_lock, flags);
 }
 
 static void gs_write_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;
+
+	/* When port is NULL, return to avoid panic. */
+	if (!port) {
+		spin_unlock_irqrestore(&serial_port_lock, flags);
+		return;
+	}
 
 	spin_lock(&port->port_lock);
+	spin_unlock(&serial_port_lock);
 	list_add(&req->list, &port->write_pool);
 	port->write_started--;
 
@@ -486,7 +509,7 @@ static void gs_write_complete(struct usb_ep *ep, struct usb_request *req)
 		break;
 	}
 
-	spin_unlock(&port->port_lock);
+	spin_unlock_irqrestore(&port->port_lock, flags);
 }
 
 static void gs_free_requests(struct usb_ep *ep, struct list_head *head,
-- 
2.39.0