usb: gadget: f_ecm: Refactor bind path to use __free()

After an bind/unbind cycle, the ecm->notify_req is left stale. If a
subsequent bind fails, the unified error label attempts to free this
stale request, leading to a NULL pointer dereference when accessing
ep->ops->free_request.

Refactor the error handling in the bind path to use the __free()
automatic cleanup mechanism.

Fixes: da741b8c56d6 ("usb ethernet gadget: split CDC Ethernet function")
Cc: [e-mail]
Signed-off-by: Kuen-Han Tsai <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/usb/gadget/function/f_ecm.c

···
 
 /* #define VERBOSE_DEBUG */
 
+#include <linux/cleanup.h>
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/etherdevice.h>
 #include <linux/string_choices.h>
+
+#include <linux/usb/gadget.h>
 
 #include "u_ether.h"
 #include "u_ether_configfs.h"
···
 	struct usb_ep		*ep;
 
 	struct f_ecm_opts	*ecm_opts;
+	struct usb_request	*request __free(free_usb_request) = NULL;
 
 	if (!can_support_ecm(cdev->gadget))
 		return -EINVAL;
···
 	/* allocate instance-specific interface IDs */
 	status = usb_interface_id(c, f);
 	if (status < 0)
-		goto fail;
+		return status;
 	ecm->ctrl_id = status;
 	ecm_iad_descriptor.bFirstInterface = status;
 
···
 
 	status = usb_interface_id(c, f);
 	if (status < 0)
-		goto fail;
+		return status;
 	ecm->data_id = status;
 
 	ecm_data_nop_intf.bInterfaceNumber = status;
 	ecm_data_intf.bInterfaceNumber = status;
 	ecm_union_desc.bSlaveInterface0 = status;
 
-	status = -ENODEV;
-
 	/* allocate instance-specific endpoints */
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ecm_in_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ecm->port.in_ep = ep;
 
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ecm_out_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ecm->port.out_ep = ep;
 
 	/* NOTE:  a status/notification endpoint is *OPTIONAL* but we
···
 	 */
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ecm_notify_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ecm->notify = ep;
 
-	status = -ENOMEM;
-
 	/* allocate notification request and buffer */
-	ecm->notify_req = usb_ep_alloc_request(ep, GFP_KERNEL);
-	if (!ecm->notify_req)
-		goto fail;
-	ecm->notify_req->buf = kmalloc(ECM_STATUS_BYTECOUNT, GFP_KERNEL);
-	if (!ecm->notify_req->buf)
-		goto fail;
-	ecm->notify_req->context = ecm;
-	ecm->notify_req->complete = ecm_notify_complete;
+	request = usb_ep_alloc_request(ep, GFP_KERNEL);
+	if (!request)
+		return -ENOMEM;
+	request->buf = kmalloc(ECM_STATUS_BYTECOUNT, GFP_KERNEL);
+	if (!request->buf)
+		return -ENOMEM;
+	request->context = ecm;
+	request->complete = ecm_notify_complete;
 
 	/* support all relevant hardware speeds... we expect that when
 	 * hardware is dual speed, all bulk-capable endpoints work at
···
 	status = usb_assign_descriptors(f, ecm_fs_function, ecm_hs_function,
 			ecm_ss_function, ecm_ss_function);
 	if (status)
-		goto fail;
+		return status;
 
 	/* NOTE:  all that is done without knowing or caring about
 	 * the network link ... which is unavailable to this code
···
 	ecm->port.open = ecm_open;
 	ecm->port.close = ecm_close;
 
+	ecm->notify_req = no_free_ptr(request);
+
 	DBG(cdev, "CDC Ethernet: IN/%s OUT/%s NOTIFY/%s\n",
 			ecm->port.in_ep->name, ecm->port.out_ep->name,
 			ecm->notify->name);
 	return 0;
-
-fail:
-	if (ecm->notify_req) {
-		kfree(ecm->notify_req->buf);
-		usb_ep_free_request(ecm->notify, ecm->notify_req);
-	}
-
-	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);
-
-	return status;
 }
 
 static inline struct f_ecm_opts *to_f_ecm_opts(struct config_item *item)