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

After an bind/unbind cycle, the ncm->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.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
Call trace:
usb_ep_free_request+0x2c/0xec
ncm_bind+0x39c/0x3dc
usb_add_function+0xcc/0x1f0
configfs_composite_bind+0x468/0x588
gadget_bind_driver+0x104/0x270
really_probe+0x190/0x374
__driver_probe_device+0xa0/0x12c
driver_probe_device+0x3c/0x218
__device_attach_driver+0x14c/0x188
bus_for_each_drv+0x10c/0x168
__device_attach+0xfc/0x198
device_initial_probe+0x14/0x24
bus_probe_device+0x94/0x11c
device_add+0x268/0x48c
usb_add_gadget+0x198/0x28c
dwc3_gadget_init+0x700/0x858
__dwc3_set_mode+0x3cc/0x664
process_scheduled_works+0x1d8/0x488
worker_thread+0x244/0x334
kthread+0x114/0x1bc
ret_from_fork+0x10/0x20

Fixes: 9f6ce4240a2b ("usb: gadget: f_ncm.c added")
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_ncm.c

···
  * Copyright (C) 2008 Nokia Corporation
  */
 
+#include <linux/cleanup.h>
 #include <linux/kernel.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
···
 #include <linux/string_choices.h>
 
 #include <linux/usb/cdc.h>
+#include <linux/usb/gadget.h>
 
 #include "u_ether.h"
 #include "u_ether_configfs.h"
···
 	struct usb_ep		*ep;
 	struct f_ncm_opts	*ncm_opts;
 
+	struct usb_os_desc_table	*os_desc_table __free(kfree) = NULL;
+	struct usb_request		*request __free(free_usb_request) = NULL;
+
 	if (!can_support_ecm(cdev->gadget))
 		return -EINVAL;
 
 	ncm_opts = container_of(f->fi, struct f_ncm_opts, func_inst);
 
 	if (cdev->use_os_string) {
-		f->os_desc_table = kzalloc(sizeof(*f->os_desc_table),
-					   GFP_KERNEL);
-		if (!f->os_desc_table)
+		os_desc_table = kzalloc(sizeof(*os_desc_table), GFP_KERNEL);
+		if (!os_desc_table)
 			return -ENOMEM;
-		f->os_desc_n = 1;
-		f->os_desc_table[0].os_desc = &ncm_opts->ncm_os_desc;
 	}
 
 	mutex_lock(&ncm_opts->lock);
···
 	mutex_unlock(&ncm_opts->lock);
 
 	if (status)
-		goto fail;
+		return status;
 
 	ncm_opts->bound = true;
 
 	us = usb_gstrings_attach(cdev, ncm_strings,
 				 ARRAY_SIZE(ncm_string_defs));
-	if (IS_ERR(us)) {
-		status = PTR_ERR(us);
-		goto fail;
-	}
+	if (IS_ERR(us))
+		return PTR_ERR(us);
+
 	ncm_control_intf.iInterface = us[STRING_CTRL_IDX].id;
 	ncm_data_nop_intf.iInterface = us[STRING_DATA_IDX].id;
 	ncm_data_intf.iInterface = us[STRING_DATA_IDX].id;
···
 	/* allocate instance-specific interface IDs */
 	status = usb_interface_id(c, f);
 	if (status < 0)
-		goto fail;
+		return status;
 	ncm->ctrl_id = status;
 	ncm_iad_desc.bFirstInterface = status;
 
 	ncm_control_intf.bInterfaceNumber = status;
 	ncm_union_desc.bMasterInterface0 = status;
 
-	if (cdev->use_os_string)
-		f->os_desc_table[0].if_id =
-			ncm_iad_desc.bFirstInterface;
-
 	status = usb_interface_id(c, f);
 	if (status < 0)
-		goto fail;
+		return status;
 	ncm->data_id = status;
 
 	ncm_data_nop_intf.bInterfaceNumber = status;
···
 
 	ecm_desc.wMaxSegmentSize = cpu_to_le16(ncm_opts->max_segment_size);
 
-	status = -ENODEV;
-
 	/* allocate instance-specific endpoints */
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ncm->port.in_ep = ep;
 
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_out_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ncm->port.out_ep = ep;
 
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_notify_desc);
 	if (!ep)
-		goto fail;
+		return -ENODEV;
 	ncm->notify = ep;
 
-	status = -ENOMEM;
-
 	/* allocate notification request and buffer */
-	ncm->notify_req = usb_ep_alloc_request(ep, GFP_KERNEL);
-	if (!ncm->notify_req)
-		goto fail;
-	ncm->notify_req->buf = kmalloc(NCM_STATUS_BYTECOUNT, GFP_KERNEL);
-	if (!ncm->notify_req->buf)
-		goto fail;
-	ncm->notify_req->context = ncm;
-	ncm->notify_req->complete = ncm_notify_complete;
+	request = usb_ep_alloc_request(ep, GFP_KERNEL);
+	if (!request)
+		return -ENOMEM;
+	request->buf = kmalloc(NCM_STATUS_BYTECOUNT, GFP_KERNEL);
+	if (!request->buf)
+		return -ENOMEM;
+	request->context = ncm;
+	request->complete = ncm_notify_complete;
 
 	/*
 	 * support all relevant hardware speeds... we expect that when
···
 	status = usb_assign_descriptors(f, ncm_fs_function, ncm_hs_function,
 			ncm_ss_function, ncm_ss_function);
 	if (status)
-		goto fail;
+		return status;
 
 	/*
 	 * NOTE:  all that is done without knowing or caring about
···
 
 	hrtimer_setup(&ncm->task_timer, ncm_tx_timeout, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
 
+	if (cdev->use_os_string) {
+		os_desc_table[0].os_desc = &ncm_opts->ncm_os_desc;
+		os_desc_table[0].if_id = ncm_iad_desc.bFirstInterface;
+		f->os_desc_table = no_free_ptr(os_desc_table);
+		f->os_desc_n = 1;
+	}
+	ncm->notify_req = no_free_ptr(request);
+
 	DBG(cdev, "CDC Network: IN/%s OUT/%s NOTIFY/%s\n",
 			ncm->port.in_ep->name, ncm->port.out_ep->name,
 			ncm->notify->name);
 	return 0;
-
-fail:
-	kfree(f->os_desc_table);
-	f->os_desc_n = 0;
-
-	if (ncm->notify_req) {
-		kfree(ncm->notify_req->buf);
-		usb_ep_free_request(ncm->notify, ncm->notify_req);
-	}
-
-	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);
-
-	return status;
 }
 
 static inline struct f_ncm_opts *to_f_ncm_opts(struct config_item *item)